Saturday, October 30, 2010
What happens when too much cylinder oil is injected in the working cylinder
What happens when too much cylinder oil is injected in the working cylinder
Gujarat plans first-of-its-kind sea dam
In a first, Gurajat is planning to build an over the sea dam in the northern portion of the Gulf of Khambat (Cambay) with an investment of over Rs 50,000 crore (Rs 500 billion).
The 35-kilometre dam project named Kalpasar Dam Alignment would lead to a sweet water reservoir. Besides, it will also have a road and rail overbridge, which will reduce the distance between Bhavnagar and Surat by 200 kilometre.
While, the main dam help generate tidal power, the reservoir is expected to supply water for drinking and agricultural purposes.
The 35-kilometre dam project named Kalpasar Dam Alignment would lead to a sweet water reservoir. Besides, it will also have a road and rail overbridge, which will reduce the distance between Bhavnagar and Surat by 200 kilometre.
While, the main dam help generate tidal power, the reservoir is expected to supply water for drinking and agricultural purposes.
Friday, October 29, 2010
Metallurgical Terms and Definitions
Aecm , Ae1 , Ae3 , Ae4:
The temperatures of phase changes at equilibrium.
Age Hardening:
Hardening by aging (heat treatment) usually after rapid cooling or cold working.
Age Softening:
Spontaneous decrease of strength and hardness that takes place at room
temperature in certain strain hardened alloys, especially those of aluminum.
Alloying Element:
An element added to and remaining in a metal that changes structure and
properties.
Annealing:
A generic term denoting a treatment consisting of heating to and holding at a suitable temperature followed by cooling at a suitable rate, used primarily to soften metallic materials, but also to simultaneously produce desired changes in other properties or in microstructure. The purpose of such changes may be, but is not confined to:improvement of machinability, facilitation of cold work, improvement of mechanical or electrical properties, and /or increase in stability of dimensions. When the term is used unqualifiedly, full annealing is implied. When applied only for the relief of stress, the process is properly call stress relieving or stress-relief annealing.
Apparent Density:
(1) The weight per unit volume of a powder, in contrast to the weight per unit volume of the individual particles. (2) The weight per unit volume of a porous solid,where the unit volume is determined from external dimensions of the mass. Apparent density is always less than the true density of the material itself.
Austenite:
A solid solution of one or more elements in face-centered cubic iron (gamma iron).
Unless otherwise designated (such as nickel austenite), the solute is generally assumed to be carbon.
Bainite:
The combination of ferrite and cementite from the austenitic state at temperature below the pearlitic range where it is difficult for carbon to diffuse into pearlite. The structure appears to be feathery in appearance and/or needle-like.
Bend Test:
A test for determining relative ductility of metal that is to be formed (usually sheet, strip, plate, or wire) and for determining soundness and toughness of metal (after welding, for example). The specimen is usually bent over a specified diameter through a specified angle for a specified number of cycles.
Brinell Hardness Number (HB):
A number related to the applied load and to the surface area of the permanent impression made by a ball indenter.
Brinell Hardness Test:
A test for determining the hardness of a material by forcing a hard steel or carbide ball of specified diameter (typically 10mm) into it under a specified load. The result is expressed as the Brinell Hardness Number.
Brittleness:
The tendency of a material to fracture without first undergoing significant plastic deformation. Contrast with ductility.
Carbon Equivalent:
(1) For cast iron, an empirical relationship of the total carbon, silicon, and phosphorus contents expressed by the formula:
CE= %C+0.3(%Si) + 0.33 (%P)
-0.027 (%Mn) + 0.4 (%S)
(2) For rating of weldability:
CE= C+ Mn + Ni + Cu + Cr + Mo + V
6 15 15 5 5 5
Carbonitriding:
A case hardening process in which a suitable ferrous material is heated above the lower transformation temperature in a gaseous atmosphere of such composition as to cause simultaneous absorption of carbon and nitrogen by the surface and , by diffusion,create a concentration gradient. The heat-treating process is completed by cooling at a rate that produces the desired properties in the workpiece.
Carburizing:
Absorption and diffusion of carbon into solid ferrous alloys by heating, to a temperature usually above Ac3, in contact with a suitable carbonaceous material. A form of case hardening that produces a carbon gradient extending inward from the surface, enabling the surface layer to be hardened either by quenching directly from the carburizing
temperature or by cooling to room temperature, then reaustenitizing and quenching.
Case:
In heat treating, that portion of a ferrous alloy, extending inward from the surface, whose composition has been altered during case hardening. Typically considered to be the portion of an alloy (a) whose composition has been measurably altered from the original composition, (b) that appears light when etched, or (c) that has a higher hardness value
than the core. Contrast with core.
Case Hardening:
A generic term covering several processed applicable to steel that change the chemical composition of the surface layer by absorption of carbon, nitrogen, or a mixture of the two and, by diffusion, create a concentration gradient. The processes commonly used are carburizing and quench hardening; cyaniding; nitriding; and carbonitriding. The use of the applicable specific process name is preferred.
Cementite:
A hard (800HV), brittle compound of iron and carbon, known chemically as iron carbide and having the approximate chemical formula Fe3C. It is characterized by an orthorhombic crystal structure. When it occurs as a phase in steel, the chemical composition will be altered by the presence of manganese and other carbide-forming elements. The highest cementite contents are observed in white cast irons, which are used in applications where high wear resistance is required.
Cold Working:
Deforming metal plastically under conditions of temperature and strain rate that induce strain hardening. Usually, but not necessarily, conducted at room temperature. Contrast with hot working.
Compression Test:
A method for assessing the ability of a material to withstand compressive loads. Analyses of structural behavior or metal forming require knowledge of compression stress-strain properties.
Compressive Strength:
The maximum compressive stress that a material is capable of developing, based on original area of cross section.
Compressive Stress:
A stress that causes an elastic body to deform (shorten) in the direction of the applied load. Contrast with tensile stress.
Defect:
(1) A discontinuity whose size, shape, orientation, or location makes it detrimental to the useful service of the part in which it occurs. (2) A discontinuity or discontinuities which by nature or accumulated effect (for example, total crack length) render a part or product unable to meet minimum applicable acceptance standards or specifications.
Die Casting:
(1) A casting made in a die. (2) A casting process in which molten metal is forced under high pressure into the cavity of a metal mold.
Metallurgical Terms and Definitions
Discontinuity:
(1) Any interruption in the normal physical structure or configuration of a part, such as cracks, laps, seams, inclusions, or porosity. A discontinuity may or may not affect the utility of the part. (2) An interruption of the typical structure of a weldment, such as a lack of homogeneity in the mechanical, metallurgical, or physical characteristics of the material or weldment. A discontinuity is not necessarily a defect.
Elasticity:
The property of a material by virtue of which deformation caused by stress
disappears upon removal of the stress.
Elongation:
A term used in mechanical testing to describe the amount of extension of a test
piece when stressed.
Engineering Strain:
A term sometimes used for average linear strain or conventional strain in order to
differentiate if from true strain. In tension testing it is calculated by dividing the change in the gage length by the original gage length.
Engineering Stress:
A term sometimes used for conventional stress in order to differentiate it from true
stress. In tension testing, it is calculated by dividing the breaking load applied to the specimen by the original cross-sectional area of the specimen.
Etching:
Subjecting the surface of a metal to preferential chemical or electrolytic attack in
order to reveal structural details for metallographic examination.
Exstensometer:
An instrument for measuring changes in length over a given gage length caused by
application or removal of a force. Commonly used in tension testing.
Extrusion:
The conversion of an ingot or billet into lengths of uniform cross section by forcing metal to flow plastically through a die orifice.
Failure:
A general term used to imply that a part in service (a) has become completely
inoperable, (b) is still operable but incapable of satisfactorily performing its intended function, or (c) has deteriorated seriously, to the point that it has become unreliable or unsafe for continued use.
Fatigue:
The phenomenon leading to fracture under repeated or fluctuating stresses having
a maximum value less than the ultimate tensile strength of the material.
Fatigue Failure:
Failure that occurs when a specimen undergoing fatigue completely fractures into
two parts of which has softened or been otherwise significantly reduced in stiffness by thermal heating or cracking.
Ferrite:
A solid solution of one or more elements in body-centered cubic iron (alpha iron).
Ferrous:
Metallic materials in which the principal component is iron.
Flowlines:
(1) Texture showing the direction of metal flow during hot or cold working. Flow
lines can often be revealed by etching the surface or a section of a metal part. (2) In mechanical metallurgy, paths followed by minute volumes of metal during deformation.
Fluorescent Penetrant Inspection:
Inspection using a fluorescent liquid that will penetrate any surface opening; after
the surface has been wiped clean, the location of any surface flaws may be detected by the fluorescence, under ultraviolet light, of back-seepage of the fluid.
Formability:
The ease with which a metal can be shaped through plastic deformation.
Evaluation of the formability of a metal involves measurement of strength, ductility, and the amount of deformation required to cause fracture.
Forming:
(1) Making a change, with the exception of shearing or blanking, in the shape or
contour of a metal part without intentionally altering its thickness. (2) The plastic deformation of a billet or a blanked sheet between tools (dies) to obtain the final configuration. Metalforming processes are typically classified as bulk forming and sheet forming. Also referred to as metalworking.
Fractography:
Descriptive treatment of fracture of materials, with specific reference to
photographs of the fracture surface.
Fracture:
The irregular surface produced when a piece of metal is broken.
Gage:
(1) The thickness of sheet or the diameter of wire. The various standards are
arbitrary and differ with regard to ferrous and nonferrous products as well as sheet and wire.
(2) An aid for visual inspection that enables an inspector to determine more reliably whether the size or contour of a formed part meets dimensional requirements.
(3) An instrument used to measure thickness or length.
Gage Length:
The original length of that portion of the specimen over which strain, change of
length and other characteristics are measured.
Grain:
An individual crystal in a polycrystalline material; it may or may not contain
twinned regions and subgrains.
Grain Boundary:
A narrow zone in a metal or ceramic corresponding to the transition from one
crystallographic orientation to another, thus separating one grain from another; the atoms in each grain are arranged in an orderly pattern.
Grain Growth:
(1) An increase in the average size of the grains in polycrystalline material, usually as a result of heating at elevated temperature.
(2) In polycrystalline materials, a phenomenon occurring fairly close below the melting point in which the larger grains grow still larger while the smallest ones gradually diminish and disappear.
Grain Size:
For metals, a measure of the areas or volumes of grains in a polycrystalline
material, usually expressed as an average when the individual sizes are fairly uniform. In metals containing two or more phases, grain size refers to that of the matrix unless otherwise specified. Grain size is reported in terms of number of grains per unit area or volume, in terms of average diameter, or as a grain-size number derived from area measurements.
Granular Fracture:
A type of irregular surface produced when metal is broken that is characterized by
a rough, grainlike appearance, rather than a smooth or fibrous one.
Hardenability:
The relative ability of a ferrous alloy to form martensite when quenched from a
temperature above the upper critical temperature.
Hardening:
Increasing hardness of metals by suitable treatment, usually involving heating and
cooling.
Hardness:
A measure of the resistance of a material to surface indentation or abrasion; may
be thought of as a function of the stress required to produce some specified type of
surface deformation.
Heat Treatment:
Heating and cooling a solid metal or alloy in such a way as to obtain desired
conditions or properties.
High Strength Low Alloy (HSLA) Steels:
Steels designed to provide better mechanical properties and/or greater resistance
to atmospheric corrosion than conventional carbon steels.
Hot Working:
The plastic deformation of metal at such a temperature and strain rate that
recrystallization takes place simultaneously with the deformation, thus avoiding any strain
hardening
Also referred to as hot forging and hot forming.
Hydrogen Embrittlement:
A process resulting in a decrease of the toughness or ductility of a metal due to the presence of atomic hydrogen. Hydrogen embrittlement has been recognized classically as being of two types. The first, known as internal hydrogen embrittlement, occurs when the hydrogen enters molten metal which becomes supersaturated with hydrogen immediately after solidification. The second type, environmental hydrogen embrittlement, results from hydrogen being absorbed by solid metals. This can occur during elevated-temperature
thermal treatments and in service during electroplating, contact with maintenance
chemicals, corrosion reactions, cathodic protection, and operating in high-pressure
hydrogen.
Impact Test:
A test for determining the energy absorbed in fracturing a test piece at high
velocity, as distinct from static test.
Impregnation:
(1) Treatment of porous castings with a sealing medium to stop pressure leaks.
(2) The process of filling the pores of a sintered compact, usually with a liquid such as a lubricant.
(3) The process of mixing particles of a non-metallic substance in a cemented carbide matrix, as in diamond-impregnated tools.
Inclusion:
A physical and mechanical discontinuity occurring within a material or part, usually
consisting of solid, encapsulated foreign material.
Induction Hardening:
A surface-hardening process in which only the surface layer of a suitable ferrous
workpiece is heated by electromagnetic induction to above the upper critical temperature and immediately quenched.
Insert:
(1) A part formed from a second material, usually a metal, which is placed in the
molds and appears as an integral structural part of the final casting. (2) A removable portion of a die or mold.
Intergranular:
Between crystals or grains. Also called intercrystalline.
Intergranular Cracking:
Cracking or fracturing that occurs between the grains or crystals in a
polycrystalline aggregate. Also called intercrystalline cracking.
Investment Casting:
(1) Casting metal into a mold produced by surrounding, or investing, an
expendable pattern with a refractory slurry coating that sets at room temperature, after which the wax or plastic pattern is removed through the us of heat prior to filling the mold with liquid metal.
(2) A part made by the investment casting process.
Killed Steel:
Steel treated with a strong deoxidizing agent such as silicon or aluminum in order
to reduce the oxygen content to such a level that no reaction occurs between carbon and oxygen during solidification.
Knoop Hardness Number (HK):
A number related to the applied load and to the projected area of the permanent
impression made by a rhombic-based pyramidal diamond indenter having included edge
angles of 172o 30’ and 130o 0’ computed from the equation:
HK= ____P____
0.07028d2
where P is applied load, kgf; and d is the long diagonal of the impression, mm. In
reporting Knoop hardness numbers, the test load is stated.
Knoop Hardness Test:
An indentation hardness test using calibrated machines to force a rhombic-based
pyramidal diamond indenter having specified edge angles, under specified conditions, into the surface of the material under test and to measure the long diagonal after removal of the load.
Low Alloy Steels:
A category of ferrous materials that exhibit mechanical properties superior to plain
carbon steels as the result of additions of such alloying elements as nickel, chromium, and molybdenum.
Machinability:
The relative ease of machining a metal.
Martensite:
Is cooling rapidly from the austenitic state to temperature below 550oF, the
resultant structure appears to have fine accucular or needle-like appearance. The structure is highly stressed and supersaturated with carbon.
Mechanical Metallurgy:
The science and technology dealing with the behavior of metals when subjected to
applied forces; often considered to be restricted to plastic working or shaping of metals.
Mechanical Properties:
The properties of a material that reveal its elastic and inelastic behavior when force
is applied, thereby indicating its suitability for mechanical applications; for example, modulus of elasticity, tensile strength, elongation, hardness, and fatigue limit.
Metallograph:
An optical instrument designed for visual observation and photomicrography of
prepared surfaces of opaque materials at magnifications of 25 to approximately 2000x.
Metallography:
The study of the structure of metals and alloys by various methods, especially by
optical and electron microscopy.
Metallurgy:
The science and technology of metals and alloys. Process metallurgy is concerned
with the extraction of metals from their ores and with refining of metals; physical
metallurgy, with physical and mechanical properties of metals as affected by composition, processing, and environmental conditions; and mechanical metallurgy, with the response of metals to applied forces.
Microhardness:
The hardness of a material as determined by forcing an indenter such as Vickers or
Knoop indenter into the surface of a material under very light load; usually, the
indentations are so small that they must be measured with a microscope.
Microhardness Test:
A microindentation hardness test using a calibrated machine to force a diamond
indenter of specific geometry, under a test load of 1 to 1000 gram-force, into the surface of the test material and to measure the diagonal or diagonals optically.
Modulus of Elasticity (E):
The measure of rigidity or stiffness of a material; the ratio of stress, below the
proportional limit, to the corresponding strain.
Morphology:
The characteristic shape, form, or surface texture or contours of the crystals,
grains, or particles of (or in) a material, generally on a microscopic scale.
Mounting:
A means by which a specimen for metallographic examination may be held during
preparation of a section surface. The specimen can be embedded in plastic or secured
mechanically in clamps.
Necking:
(1) The reduction of the cross-sectional area of a material in a localized area by
uniaxial tension or by stretching.
(2) The reduction of the diameter of a portion of the length of a cylindrical shell or tube.
Nitriding:
Introducing nitrogen into the surface layer of a solid ferrous alloy by holding at a
suitable temperature (below Ac1 for ferritic steels) in contact with a nitrogenous material, usually ammonia or molten cyanide of appropriate composition. Quenching is not required to produce a hard case.
Nitrocarburizing:
Any of several processes in which both nitrogen and carbon are absorbed into the
surface layers of a ferrous material at temperatures below the lower critical temperature and, by diffusion, create a concentration gradient. Nitrocarburizing is performed primarily to provide an antiscuffing surface layer and to improve fatigue resistance.
Oxidation:
(1) A reaction in which there is an increase in valence resulting from a loss of
electrons. Contrast with reduction.
(2) A corrosion reaction in which the corroded metal forms an oxide; usually applied to reaction with a gas containing elemental oxygen, such as air.
(3) A chemical reaction in which one substance is changed to another by oxygen combination with the substance. Much of the dross from holding and melting furnaces is the result of oxidation of the alloy held in the furnace.
Pearlite:
A metastable lamellar aggregate of ferrite and cementite resulting from the
transformation of austenite at temperatures above the bainite range.
Permanent Set:
The deformation remaining after a specimen has been stressed a prescribed amount
in tension, compression, or shear for a specified time period and released for a specified time period.
Phosphating:
Forming an adherent phosphate coating on a metal by immersion in a suitable
aqueous phosphate solution.
Physical Metallurgy:
The science and technology dealing with the properties of metals and alloys, and of
the effects of composition, processing, and environment on these properties.
Plastic Deformation:
The permanent (inelastic) distortion of materials under applied stresses that strain
the material beyond its elastic limit.
Plasticity:
The property of a material which allows it to be repeatedly deformed without
rupture when acted upon by a force sufficient to cause deformation and which allows it to retain its shape after the applied force has been removed.
Plastic Strain Ratio (r-value):
In formability testing of metals, the ratio of the true width strain to the true
thickness strain in a sheet tensile, r = ew et. A formability parameter that relates to drawing, it is also known as the anisotropy factor. A high r-value indicated a material with good drawing properties.
Plug:
(1) A rod or mandrel over which a pierced tube is forces.
(2) A rod or mandrel
that fills a tube as it is drawn through a die.
(3) A punch or mandrel over which a cup is drawn.
(4) A protruding portion of a die impression for forming a corresponding recess in the forging.
(5) A false bottom in a die.
Polishing:
(1) A surface-finishing process for ceramics and metals utilizing successive grades
of abrasive.
(2) Smoothing metal surfaces, often to a high luster, by rubbing the surface with a fine abrasive, usually contained in a cloth or other soft lap. Results in microscopic flow of some surface metal together with actual removal of a small amount of surface
metal.
(3) Removal of material by the action of abrasive grains carried to the work by a flexible support, generally either a wheel or a coated abrasive belt. (4) A mechanical, chemical, or electrolytic process or combination thereof used to prepare a smooth, reflective surface suitable for microstructural examination that is free of artifacts or damage introduced during prior sectioning or grinding.
Polycrystalline:
Pertaining to a solid comprised of many crystals or crystallites, intimately bonded
together. May be homogeneous (one substance) or heterogeneous (two or more crystal
types or compositions).
Porosity:
(1) Fine holes or pores within a solid; the amount of these pores is expressed as a
percentage of the total volume of the solid.
(2) Cavity-type discontinuities in weldments formed by gas entrapment during solidification.
(3) A characteristic of being porous, with voids or pores resulting from trapped air or shrinkage in a casting.
Powder Metallurgy:
The technology and art of producing metal powders and utilizing metal powders
for production of massive materials and shaped objects.
Powder Metallurgy Part:
A shaped object that has been formed from metal powders and sintered by heating
below the melting point of the major constituent. A structural or mechanical component made by the powder metallurgy process.
Preheating:
Heating before some further thermal or mechanical treatment. For tool steel,
heating to an intermediate temperature immediately before final austenizing. For some nonferrous alloys, heating to a high temperature for a long time, in order to homogenize the structure before working. In powder metallurgy, an early stage in the sintering procedure when, in a continuous furnace, lubricant or binder burnoff occurs without atmosphere protection prior to actual sintering in the protective atmosphere of the high heat chamber.
Quenching:
Rapid cooling of metals (often steels) from a suitable elevated temperature. This
generally is accomplished by immersion in water, oil, polymer solution, or salt, although forced air is sometimes used.
Quenching Crack:
Fracture of a metal during quenching from elevated temperature. Most frequently
observed in hardened carbon steel, alloy steel, or tool steel parts of high hardness and low toughness. Cracks often emanate from fillets, holes, corners, or other stress raisers and result from high stresses due to the volume changes accompanying transformation to
martensite.
Recarburize:
(1) To increase the carbon content of molten cast iron or steel by adding
carbonaceous material, high-carbon pig iron, or a high-carbon alloy. (2) To carburize a metal part to return surface carbon lost in processing; also known as carbon restoration.
Recrystallization:
(1) The formation of a new, strain-free grain structure from that existing in coldworked
metal, usually accomplished by heating.
(2) The change from one crystal structure
to another, as occurs on heating or cooling through a critical temperature. (3) A process, usually physical, by which one crystal species is grown at the expense of another or at the expense of others of the same substance but smaller in size.
Residual Stress:
(1) The stress existing in a body at rest, in equilibrium, at uniform temperature, and not subjected to external forces. Often caused by the forming or thermal processing curing process.
(2) An internal stress not depending on external forces resulting from such factors as cold working, phase changes, or temperature gradients.
(3) Stress present in a body that is free of external forces or thermal gradients. (4) Stress remaining in a structure or member as a result of thermal or mechanical treatment or both. Stress arises in fusion welding primarily because the weld metal contracts on cooling from the solidus to room temperature.
Rockwell Hardness Test:
An indentation hardness test using a calibrated machine that utilizes the depth of
indentation, under constant load, as a measure of hardness.
Rockwell Superficial Hardness Test:
The same test as used to determine the Rockwell hardness number except that
smaller minor and major loads are used. In Rockwell testing, the minor load is 10kgf, and the major load is 60, 100, or 150 kgf. In superficial Rockwell testing, the minor load is 3kgf, and major loads are 15, 30, or 45 kgf. In both tests, the indenter may be either a diamond cone or a steel ball, depending principally on the characteristics of the material being tested.
Roughness:
(1) Relatively finely spaced surface irregularities, the heights, widths, and
directions of which establish the predominant surface pattern. (2) The microscopic peakto-
valley distances of surface protuberances and depressions.
Segregation:
(1) Nonuniform distribution of alloying elements, impurities, or microphases in
metals and alloys.
(2) A casting defect involving a concentration of alloying elements at specific regions, usually as a result of the primary crystallization of one phase with the subsequent concentration of other elements in the remaining liquid. Microsegregation refers to normal segregation on a microscopic scale in which material richer in an alloying element freezes in successive layers on the dendrites (coring) and in constituent network. Macrosegregation refers to gross differences in concentration (for example, from one area of a casting to another). Shear Bands:
(1) Bands of very high shear strain that are observed during rolling of sheet metal.
During rolling, these form at approximately 35o to the rolling plane, parallel to the transverse direction. They are independent of grain orientation and at high strain rates traverse the entire thickness of the rolled sheet. (2) Highly localized deformation zones in metals that are observed at very high strain rates, such as those produced by high velocity (100 to 3600 m/s, or 330 to 11,800 ft/s) projectile impacts or explosive rupture.
Shore Hardness:
A measure of the resistance of material to indentation by a spring-loaded indenter
during Sceleroscope hardness testing. The higher the number, the greater the resistance. Normally used for rubber materials.
Solidification:
The change in state from liquid to solid upon cooling through the melting
temperature or melting range.
Spheroidite:
A structure of global carbide in a matrix of soft ferrite.
Steel:
An iron-base alloy, malleable in some temperature ranges as initially cast,
containing manganese, usually carbon, and often other alloying elements. In carbon steel and low-alloy steel, the maximum carbon is about 2.0%; in high-alloy steel, about 2.5%.
The dividing line between low-alloy and high-alloy steels is generally regarded as being at about 5% metallic alloying elements.
Steel is said to be differentiated from two general classes of “irons”: the cast irons, on the high-carbon side, and the relatively pure irons such as ingot iron, carbonyl iron, and electrolytic iron, on the low-carbon side. In some steels containing extremely low carbon, the manganese content is the principal differentiating factor, steel usually containing at least 0.25% and ingot iron considerably less.
Strain Hardening:
An increase in hardness and strength of metals caused by plastic deformation at
temperatures below the re-crystallization range. Also known as work hardening.
Stress Relieving:
Heating to a suitable temperature, holding long enough to reduce residual stresses,
and then cooling slowly enough to minimize the development of new residual stresses.
Structure:
As applies to a crystal, the shape and size of the unit cell and the location of all
atoms within the unit cell. As applied to microstructure, the size, shape, and arrangement of phases.
Swage:
(1) The operation of reducing or changing the cross-section area of stock by the
fast impact of revolving dies. (2) The tapering of bar, rod, wire, or tubing by forging, hammering, or squeezing; reducing a section by progressively tapering lengthwise until the entire section attains the smaller dimension of the taper.
Tensile Strength:
In tensile testing, the ratio of maximum load to original cross-sectional area. Also
called ultimate strength.
Tensile Stress:
A stress that causes two parts of an elastic body, on either side of a typical stress plane, to pull apart.
Tension:
The force or load that produces elongation.
Tension Testing:
A method of determining the behavior of materials subjected to uniaxial loading,
which tends to stretch the material. A longitudinal specimen of known length and
diameter is gripped at both ends and stretched at a slow, controlled rate until rupture occurs. Also known as tensile testing.
Torsion:
(1) A twisting deformation of a solid or tubular body about an axis in which lines
that were initially parallel to the axis become helices. (2) A twisting action resulting in shear stresses and strains.
Transformation Temperature:
The temperature at which a change in phase occurs. This term is sometimes used
to denote the limiting temperature of a transformation range. The following symbols are used for irons and steel:
Accm. In hypereutectoid steel, the temperature at which a solution of cementite in austenite is completed during heating.
Ac1. The temperature at which austenite begins to form during heating.
Ac3. The temperature at which transformation of ferrite to austenite is completed during
heating.
Ac4. The temperature at which austenite transforms to delta ferrite during heating.
Aecm , Ae1 , Ae3 , Ae4. The temperatures of phase changes at equilibrium.
Arcm. In hypereutectoid steel, the temperature at which precipitation of cementite starts during cooling.
Ar1. The temperature at which transformation of austenite to ferrite or to ferrite plus
cementite is completed during cooling.
Ar3. The temperature at which austenite begins to transform to ferrite during cooling.
Ar4. The temperature at which delta ferrite transforms to austenite during cooling.
Ar-. The temperature at which transformation of austenite to pearlite starts during
cooling.
Mf. The temperature at which transformation of austenite to martensite is completed
during cooling.
Ms (or Ar.). The temperature at which transformation of austenite to martensite starts during cooling.
Note: All these changes, except formation of martensite, occur at lower temperatures
during cooling than during heating, and depend on the rate of change of temperature.
Transgranular:
Through or across crystals or grains. Also called intracrystalline or
transcrystalline.
Transition Phase:
A nonequilibrium state that appears in a chemical system in the course of
transformation between two equilibrium states.
Transverse Direction:
Literally, “across,” usually signifying a direction or plane perpendicular to the
direction of working. In rolled plate or sheet, the direction across the width is often called long transverse: the direction through the thickness, short transverse.
True Strain:
(1) The ratio of the change in dimension, resulting from a given load increment, to
the magnitude of the dimension immediately prior to applying the load increment. (2) In a body subjected to axial force, the natural logarithm of the ratio of the gage length at the moment of observation to the original gage length. Also known as natural strain.
True Stress:
The value obtained by dividing the load applied to a member at a given instant by
the cross-sectional area over which it acts.
Ultimate Strength:
The maximum stress (tensile, compressive, or shear) a material can sustain without
fracture; determined by dividing maximum load by the original cross-sectional area of the specimen. Also known as nominal strength or maximum strength.
Ultimate Tensile Strength:
The ultimate or final (highest) stress sustained by a specimen in a tension test.
Upset:
(1) The localized increase in cross-sectional area of a workpiece or weldment
resulting from the application of pressure during mechanical fabrication or welding.
(2) That portion of a welding cycle during which the cross-sectional area is increased by the application of pressure.
(3) Bulk deformation resulting from the application of pressure in welding. The upset may be measured as a percent increase in interfacial area, a reduction in length, or a percent reduction in thickness (for lap joints).
Upsetting:
The working of metal so that the cross-sectional area of a portion or all of the
stock is increased.
Vickers Hardness Number (HV):
A number related to the applied load and the surface area of the permanent
impression made by a square-based pyramidal diamond indenter having included face
angles of 136o, computed form:
HV= 2P sin a/2 = 1.8544P
d2 d2 where P is applied load (kgf), d is mean diagonal of the impression (mm), and is the face angle of the indenter (136o).
Vicker Hardness Test:
A microindentation hardness test employing a 136o diamond pyramid indenter
(Vickers) and variable load, enabling the use of one hardness scale for all ranges of hardness-from very soft lead to tungsten carbide. Also known as diamond pyramid
hardness test.
Weldability:
A Specific or relative measure of the ability of a material to be welded under a
given set of conditions. Implicit in this definition is the ability of the completed weldment to fulfill all functions for which the part was designed.
Yield:
(1) Evidence of plastic deformation in structural materials. Also known as plastic
flow or creep.
(2) The ratio of the number of acceptable items produced in a production run to the total number that were attempted to be produced.
(3) Comparison of casting weight to the total weight of metal poured into the mold.
Yield Point:
The first stress in a material, usually less than the maximum attainable stress, at
which an increase in strain occurs without an increase in stress. Only certain materialsthose which exhibit a localized, heterogeneous type of transition from elastic to plastic deformation-produce a yield point. If there is a decrease in stress after yielding, a distinction may be made between upper and lower yield points. The load at which a sudden drop in the flow curve occurs is called the upper yield point. The constant load shown on the flow curve is the lower yield point.
Yield Strength:
The stress at which a material exhibits a specified deviation from proportionality of stress and strain. An offset of 0.2% is used for many materials, particularly metals.
Yield Stress:
The stress level of highly ductile materials at which large strains take place without further increase in stress.
Youngs Modulus:
A term used synonymously with modulus of elasticity. The ratio of tensile or
compressive stresses to the resulting strain.
The temperatures of phase changes at equilibrium.
Age Hardening:
Hardening by aging (heat treatment) usually after rapid cooling or cold working.
Age Softening:
Spontaneous decrease of strength and hardness that takes place at room
temperature in certain strain hardened alloys, especially those of aluminum.
Alloying Element:
An element added to and remaining in a metal that changes structure and
properties.
Annealing:
A generic term denoting a treatment consisting of heating to and holding at a suitable temperature followed by cooling at a suitable rate, used primarily to soften metallic materials, but also to simultaneously produce desired changes in other properties or in microstructure. The purpose of such changes may be, but is not confined to:improvement of machinability, facilitation of cold work, improvement of mechanical or electrical properties, and /or increase in stability of dimensions. When the term is used unqualifiedly, full annealing is implied. When applied only for the relief of stress, the process is properly call stress relieving or stress-relief annealing.
Apparent Density:
(1) The weight per unit volume of a powder, in contrast to the weight per unit volume of the individual particles. (2) The weight per unit volume of a porous solid,where the unit volume is determined from external dimensions of the mass. Apparent density is always less than the true density of the material itself.
Austenite:
A solid solution of one or more elements in face-centered cubic iron (gamma iron).
Unless otherwise designated (such as nickel austenite), the solute is generally assumed to be carbon.
Bainite:
The combination of ferrite and cementite from the austenitic state at temperature below the pearlitic range where it is difficult for carbon to diffuse into pearlite. The structure appears to be feathery in appearance and/or needle-like.
Bend Test:
A test for determining relative ductility of metal that is to be formed (usually sheet, strip, plate, or wire) and for determining soundness and toughness of metal (after welding, for example). The specimen is usually bent over a specified diameter through a specified angle for a specified number of cycles.
Brinell Hardness Number (HB):
A number related to the applied load and to the surface area of the permanent impression made by a ball indenter.
Brinell Hardness Test:
A test for determining the hardness of a material by forcing a hard steel or carbide ball of specified diameter (typically 10mm) into it under a specified load. The result is expressed as the Brinell Hardness Number.
Brittleness:
The tendency of a material to fracture without first undergoing significant plastic deformation. Contrast with ductility.
Carbon Equivalent:
(1) For cast iron, an empirical relationship of the total carbon, silicon, and phosphorus contents expressed by the formula:
CE= %C+0.3(%Si) + 0.33 (%P)
-0.027 (%Mn) + 0.4 (%S)
(2) For rating of weldability:
CE= C+ Mn + Ni + Cu + Cr + Mo + V
6 15 15 5 5 5
Carbonitriding:
A case hardening process in which a suitable ferrous material is heated above the lower transformation temperature in a gaseous atmosphere of such composition as to cause simultaneous absorption of carbon and nitrogen by the surface and , by diffusion,create a concentration gradient. The heat-treating process is completed by cooling at a rate that produces the desired properties in the workpiece.
Carburizing:
Absorption and diffusion of carbon into solid ferrous alloys by heating, to a temperature usually above Ac3, in contact with a suitable carbonaceous material. A form of case hardening that produces a carbon gradient extending inward from the surface, enabling the surface layer to be hardened either by quenching directly from the carburizing
temperature or by cooling to room temperature, then reaustenitizing and quenching.
Case:
In heat treating, that portion of a ferrous alloy, extending inward from the surface, whose composition has been altered during case hardening. Typically considered to be the portion of an alloy (a) whose composition has been measurably altered from the original composition, (b) that appears light when etched, or (c) that has a higher hardness value
than the core. Contrast with core.
Case Hardening:
A generic term covering several processed applicable to steel that change the chemical composition of the surface layer by absorption of carbon, nitrogen, or a mixture of the two and, by diffusion, create a concentration gradient. The processes commonly used are carburizing and quench hardening; cyaniding; nitriding; and carbonitriding. The use of the applicable specific process name is preferred.
Cementite:
A hard (800HV), brittle compound of iron and carbon, known chemically as iron carbide and having the approximate chemical formula Fe3C. It is characterized by an orthorhombic crystal structure. When it occurs as a phase in steel, the chemical composition will be altered by the presence of manganese and other carbide-forming elements. The highest cementite contents are observed in white cast irons, which are used in applications where high wear resistance is required.
Cold Working:
Deforming metal plastically under conditions of temperature and strain rate that induce strain hardening. Usually, but not necessarily, conducted at room temperature. Contrast with hot working.
Compression Test:
A method for assessing the ability of a material to withstand compressive loads. Analyses of structural behavior or metal forming require knowledge of compression stress-strain properties.
Compressive Strength:
The maximum compressive stress that a material is capable of developing, based on original area of cross section.
Compressive Stress:
A stress that causes an elastic body to deform (shorten) in the direction of the applied load. Contrast with tensile stress.
Defect:
(1) A discontinuity whose size, shape, orientation, or location makes it detrimental to the useful service of the part in which it occurs. (2) A discontinuity or discontinuities which by nature or accumulated effect (for example, total crack length) render a part or product unable to meet minimum applicable acceptance standards or specifications.
Die Casting:
(1) A casting made in a die. (2) A casting process in which molten metal is forced under high pressure into the cavity of a metal mold.
Metallurgical Terms and Definitions
Discontinuity:
(1) Any interruption in the normal physical structure or configuration of a part, such as cracks, laps, seams, inclusions, or porosity. A discontinuity may or may not affect the utility of the part. (2) An interruption of the typical structure of a weldment, such as a lack of homogeneity in the mechanical, metallurgical, or physical characteristics of the material or weldment. A discontinuity is not necessarily a defect.
Elasticity:
The property of a material by virtue of which deformation caused by stress
disappears upon removal of the stress.
Elongation:
A term used in mechanical testing to describe the amount of extension of a test
piece when stressed.
Engineering Strain:
A term sometimes used for average linear strain or conventional strain in order to
differentiate if from true strain. In tension testing it is calculated by dividing the change in the gage length by the original gage length.
Engineering Stress:
A term sometimes used for conventional stress in order to differentiate it from true
stress. In tension testing, it is calculated by dividing the breaking load applied to the specimen by the original cross-sectional area of the specimen.
Etching:
Subjecting the surface of a metal to preferential chemical or electrolytic attack in
order to reveal structural details for metallographic examination.
Exstensometer:
An instrument for measuring changes in length over a given gage length caused by
application or removal of a force. Commonly used in tension testing.
Extrusion:
The conversion of an ingot or billet into lengths of uniform cross section by forcing metal to flow plastically through a die orifice.
Failure:
A general term used to imply that a part in service (a) has become completely
inoperable, (b) is still operable but incapable of satisfactorily performing its intended function, or (c) has deteriorated seriously, to the point that it has become unreliable or unsafe for continued use.
Fatigue:
The phenomenon leading to fracture under repeated or fluctuating stresses having
a maximum value less than the ultimate tensile strength of the material.
Fatigue Failure:
Failure that occurs when a specimen undergoing fatigue completely fractures into
two parts of which has softened or been otherwise significantly reduced in stiffness by thermal heating or cracking.
Ferrite:
A solid solution of one or more elements in body-centered cubic iron (alpha iron).
Ferrous:
Metallic materials in which the principal component is iron.
Flowlines:
(1) Texture showing the direction of metal flow during hot or cold working. Flow
lines can often be revealed by etching the surface or a section of a metal part. (2) In mechanical metallurgy, paths followed by minute volumes of metal during deformation.
Fluorescent Penetrant Inspection:
Inspection using a fluorescent liquid that will penetrate any surface opening; after
the surface has been wiped clean, the location of any surface flaws may be detected by the fluorescence, under ultraviolet light, of back-seepage of the fluid.
Formability:
The ease with which a metal can be shaped through plastic deformation.
Evaluation of the formability of a metal involves measurement of strength, ductility, and the amount of deformation required to cause fracture.
Forming:
(1) Making a change, with the exception of shearing or blanking, in the shape or
contour of a metal part without intentionally altering its thickness. (2) The plastic deformation of a billet or a blanked sheet between tools (dies) to obtain the final configuration. Metalforming processes are typically classified as bulk forming and sheet forming. Also referred to as metalworking.
Fractography:
Descriptive treatment of fracture of materials, with specific reference to
photographs of the fracture surface.
Fracture:
The irregular surface produced when a piece of metal is broken.
Gage:
(1) The thickness of sheet or the diameter of wire. The various standards are
arbitrary and differ with regard to ferrous and nonferrous products as well as sheet and wire.
(2) An aid for visual inspection that enables an inspector to determine more reliably whether the size or contour of a formed part meets dimensional requirements.
(3) An instrument used to measure thickness or length.
Gage Length:
The original length of that portion of the specimen over which strain, change of
length and other characteristics are measured.
Grain:
An individual crystal in a polycrystalline material; it may or may not contain
twinned regions and subgrains.
Grain Boundary:
A narrow zone in a metal or ceramic corresponding to the transition from one
crystallographic orientation to another, thus separating one grain from another; the atoms in each grain are arranged in an orderly pattern.
Grain Growth:
(1) An increase in the average size of the grains in polycrystalline material, usually as a result of heating at elevated temperature.
(2) In polycrystalline materials, a phenomenon occurring fairly close below the melting point in which the larger grains grow still larger while the smallest ones gradually diminish and disappear.
Grain Size:
For metals, a measure of the areas or volumes of grains in a polycrystalline
material, usually expressed as an average when the individual sizes are fairly uniform. In metals containing two or more phases, grain size refers to that of the matrix unless otherwise specified. Grain size is reported in terms of number of grains per unit area or volume, in terms of average diameter, or as a grain-size number derived from area measurements.
Granular Fracture:
A type of irregular surface produced when metal is broken that is characterized by
a rough, grainlike appearance, rather than a smooth or fibrous one.
Hardenability:
The relative ability of a ferrous alloy to form martensite when quenched from a
temperature above the upper critical temperature.
Hardening:
Increasing hardness of metals by suitable treatment, usually involving heating and
cooling.
Hardness:
A measure of the resistance of a material to surface indentation or abrasion; may
be thought of as a function of the stress required to produce some specified type of
surface deformation.
Heat Treatment:
Heating and cooling a solid metal or alloy in such a way as to obtain desired
conditions or properties.
High Strength Low Alloy (HSLA) Steels:
Steels designed to provide better mechanical properties and/or greater resistance
to atmospheric corrosion than conventional carbon steels.
Hot Working:
The plastic deformation of metal at such a temperature and strain rate that
recrystallization takes place simultaneously with the deformation, thus avoiding any strain
hardening
Also referred to as hot forging and hot forming.
Hydrogen Embrittlement:
A process resulting in a decrease of the toughness or ductility of a metal due to the presence of atomic hydrogen. Hydrogen embrittlement has been recognized classically as being of two types. The first, known as internal hydrogen embrittlement, occurs when the hydrogen enters molten metal which becomes supersaturated with hydrogen immediately after solidification. The second type, environmental hydrogen embrittlement, results from hydrogen being absorbed by solid metals. This can occur during elevated-temperature
thermal treatments and in service during electroplating, contact with maintenance
chemicals, corrosion reactions, cathodic protection, and operating in high-pressure
hydrogen.
Impact Test:
A test for determining the energy absorbed in fracturing a test piece at high
velocity, as distinct from static test.
Impregnation:
(1) Treatment of porous castings with a sealing medium to stop pressure leaks.
(2) The process of filling the pores of a sintered compact, usually with a liquid such as a lubricant.
(3) The process of mixing particles of a non-metallic substance in a cemented carbide matrix, as in diamond-impregnated tools.
Inclusion:
A physical and mechanical discontinuity occurring within a material or part, usually
consisting of solid, encapsulated foreign material.
Induction Hardening:
A surface-hardening process in which only the surface layer of a suitable ferrous
workpiece is heated by electromagnetic induction to above the upper critical temperature and immediately quenched.
Insert:
(1) A part formed from a second material, usually a metal, which is placed in the
molds and appears as an integral structural part of the final casting. (2) A removable portion of a die or mold.
Intergranular:
Between crystals or grains. Also called intercrystalline.
Intergranular Cracking:
Cracking or fracturing that occurs between the grains or crystals in a
polycrystalline aggregate. Also called intercrystalline cracking.
Investment Casting:
(1) Casting metal into a mold produced by surrounding, or investing, an
expendable pattern with a refractory slurry coating that sets at room temperature, after which the wax or plastic pattern is removed through the us of heat prior to filling the mold with liquid metal.
(2) A part made by the investment casting process.
Killed Steel:
Steel treated with a strong deoxidizing agent such as silicon or aluminum in order
to reduce the oxygen content to such a level that no reaction occurs between carbon and oxygen during solidification.
Knoop Hardness Number (HK):
A number related to the applied load and to the projected area of the permanent
impression made by a rhombic-based pyramidal diamond indenter having included edge
angles of 172o 30’ and 130o 0’ computed from the equation:
HK= ____P____
0.07028d2
where P is applied load, kgf; and d is the long diagonal of the impression, mm. In
reporting Knoop hardness numbers, the test load is stated.
Knoop Hardness Test:
An indentation hardness test using calibrated machines to force a rhombic-based
pyramidal diamond indenter having specified edge angles, under specified conditions, into the surface of the material under test and to measure the long diagonal after removal of the load.
Low Alloy Steels:
A category of ferrous materials that exhibit mechanical properties superior to plain
carbon steels as the result of additions of such alloying elements as nickel, chromium, and molybdenum.
Machinability:
The relative ease of machining a metal.
Martensite:
Is cooling rapidly from the austenitic state to temperature below 550oF, the
resultant structure appears to have fine accucular or needle-like appearance. The structure is highly stressed and supersaturated with carbon.
Mechanical Metallurgy:
The science and technology dealing with the behavior of metals when subjected to
applied forces; often considered to be restricted to plastic working or shaping of metals.
Mechanical Properties:
The properties of a material that reveal its elastic and inelastic behavior when force
is applied, thereby indicating its suitability for mechanical applications; for example, modulus of elasticity, tensile strength, elongation, hardness, and fatigue limit.
Metallograph:
An optical instrument designed for visual observation and photomicrography of
prepared surfaces of opaque materials at magnifications of 25 to approximately 2000x.
Metallography:
The study of the structure of metals and alloys by various methods, especially by
optical and electron microscopy.
Metallurgy:
The science and technology of metals and alloys. Process metallurgy is concerned
with the extraction of metals from their ores and with refining of metals; physical
metallurgy, with physical and mechanical properties of metals as affected by composition, processing, and environmental conditions; and mechanical metallurgy, with the response of metals to applied forces.
Microhardness:
The hardness of a material as determined by forcing an indenter such as Vickers or
Knoop indenter into the surface of a material under very light load; usually, the
indentations are so small that they must be measured with a microscope.
Microhardness Test:
A microindentation hardness test using a calibrated machine to force a diamond
indenter of specific geometry, under a test load of 1 to 1000 gram-force, into the surface of the test material and to measure the diagonal or diagonals optically.
Modulus of Elasticity (E):
The measure of rigidity or stiffness of a material; the ratio of stress, below the
proportional limit, to the corresponding strain.
Morphology:
The characteristic shape, form, or surface texture or contours of the crystals,
grains, or particles of (or in) a material, generally on a microscopic scale.
Mounting:
A means by which a specimen for metallographic examination may be held during
preparation of a section surface. The specimen can be embedded in plastic or secured
mechanically in clamps.
Necking:
(1) The reduction of the cross-sectional area of a material in a localized area by
uniaxial tension or by stretching.
(2) The reduction of the diameter of a portion of the length of a cylindrical shell or tube.
Nitriding:
Introducing nitrogen into the surface layer of a solid ferrous alloy by holding at a
suitable temperature (below Ac1 for ferritic steels) in contact with a nitrogenous material, usually ammonia or molten cyanide of appropriate composition. Quenching is not required to produce a hard case.
Nitrocarburizing:
Any of several processes in which both nitrogen and carbon are absorbed into the
surface layers of a ferrous material at temperatures below the lower critical temperature and, by diffusion, create a concentration gradient. Nitrocarburizing is performed primarily to provide an antiscuffing surface layer and to improve fatigue resistance.
Oxidation:
(1) A reaction in which there is an increase in valence resulting from a loss of
electrons. Contrast with reduction.
(2) A corrosion reaction in which the corroded metal forms an oxide; usually applied to reaction with a gas containing elemental oxygen, such as air.
(3) A chemical reaction in which one substance is changed to another by oxygen combination with the substance. Much of the dross from holding and melting furnaces is the result of oxidation of the alloy held in the furnace.
Pearlite:
A metastable lamellar aggregate of ferrite and cementite resulting from the
transformation of austenite at temperatures above the bainite range.
Permanent Set:
The deformation remaining after a specimen has been stressed a prescribed amount
in tension, compression, or shear for a specified time period and released for a specified time period.
Phosphating:
Forming an adherent phosphate coating on a metal by immersion in a suitable
aqueous phosphate solution.
Physical Metallurgy:
The science and technology dealing with the properties of metals and alloys, and of
the effects of composition, processing, and environment on these properties.
Plastic Deformation:
The permanent (inelastic) distortion of materials under applied stresses that strain
the material beyond its elastic limit.
Plasticity:
The property of a material which allows it to be repeatedly deformed without
rupture when acted upon by a force sufficient to cause deformation and which allows it to retain its shape after the applied force has been removed.
Plastic Strain Ratio (r-value):
In formability testing of metals, the ratio of the true width strain to the true
thickness strain in a sheet tensile, r = ew et. A formability parameter that relates to drawing, it is also known as the anisotropy factor. A high r-value indicated a material with good drawing properties.
Plug:
(1) A rod or mandrel over which a pierced tube is forces.
(2) A rod or mandrel
that fills a tube as it is drawn through a die.
(3) A punch or mandrel over which a cup is drawn.
(4) A protruding portion of a die impression for forming a corresponding recess in the forging.
(5) A false bottom in a die.
Polishing:
(1) A surface-finishing process for ceramics and metals utilizing successive grades
of abrasive.
(2) Smoothing metal surfaces, often to a high luster, by rubbing the surface with a fine abrasive, usually contained in a cloth or other soft lap. Results in microscopic flow of some surface metal together with actual removal of a small amount of surface
metal.
(3) Removal of material by the action of abrasive grains carried to the work by a flexible support, generally either a wheel or a coated abrasive belt. (4) A mechanical, chemical, or electrolytic process or combination thereof used to prepare a smooth, reflective surface suitable for microstructural examination that is free of artifacts or damage introduced during prior sectioning or grinding.
Polycrystalline:
Pertaining to a solid comprised of many crystals or crystallites, intimately bonded
together. May be homogeneous (one substance) or heterogeneous (two or more crystal
types or compositions).
Porosity:
(1) Fine holes or pores within a solid; the amount of these pores is expressed as a
percentage of the total volume of the solid.
(2) Cavity-type discontinuities in weldments formed by gas entrapment during solidification.
(3) A characteristic of being porous, with voids or pores resulting from trapped air or shrinkage in a casting.
Powder Metallurgy:
The technology and art of producing metal powders and utilizing metal powders
for production of massive materials and shaped objects.
Powder Metallurgy Part:
A shaped object that has been formed from metal powders and sintered by heating
below the melting point of the major constituent. A structural or mechanical component made by the powder metallurgy process.
Preheating:
Heating before some further thermal or mechanical treatment. For tool steel,
heating to an intermediate temperature immediately before final austenizing. For some nonferrous alloys, heating to a high temperature for a long time, in order to homogenize the structure before working. In powder metallurgy, an early stage in the sintering procedure when, in a continuous furnace, lubricant or binder burnoff occurs without atmosphere protection prior to actual sintering in the protective atmosphere of the high heat chamber.
Quenching:
Rapid cooling of metals (often steels) from a suitable elevated temperature. This
generally is accomplished by immersion in water, oil, polymer solution, or salt, although forced air is sometimes used.
Quenching Crack:
Fracture of a metal during quenching from elevated temperature. Most frequently
observed in hardened carbon steel, alloy steel, or tool steel parts of high hardness and low toughness. Cracks often emanate from fillets, holes, corners, or other stress raisers and result from high stresses due to the volume changes accompanying transformation to
martensite.
Recarburize:
(1) To increase the carbon content of molten cast iron or steel by adding
carbonaceous material, high-carbon pig iron, or a high-carbon alloy. (2) To carburize a metal part to return surface carbon lost in processing; also known as carbon restoration.
Recrystallization:
(1) The formation of a new, strain-free grain structure from that existing in coldworked
metal, usually accomplished by heating.
(2) The change from one crystal structure
to another, as occurs on heating or cooling through a critical temperature. (3) A process, usually physical, by which one crystal species is grown at the expense of another or at the expense of others of the same substance but smaller in size.
Residual Stress:
(1) The stress existing in a body at rest, in equilibrium, at uniform temperature, and not subjected to external forces. Often caused by the forming or thermal processing curing process.
(2) An internal stress not depending on external forces resulting from such factors as cold working, phase changes, or temperature gradients.
(3) Stress present in a body that is free of external forces or thermal gradients. (4) Stress remaining in a structure or member as a result of thermal or mechanical treatment or both. Stress arises in fusion welding primarily because the weld metal contracts on cooling from the solidus to room temperature.
Rockwell Hardness Test:
An indentation hardness test using a calibrated machine that utilizes the depth of
indentation, under constant load, as a measure of hardness.
Rockwell Superficial Hardness Test:
The same test as used to determine the Rockwell hardness number except that
smaller minor and major loads are used. In Rockwell testing, the minor load is 10kgf, and the major load is 60, 100, or 150 kgf. In superficial Rockwell testing, the minor load is 3kgf, and major loads are 15, 30, or 45 kgf. In both tests, the indenter may be either a diamond cone or a steel ball, depending principally on the characteristics of the material being tested.
Roughness:
(1) Relatively finely spaced surface irregularities, the heights, widths, and
directions of which establish the predominant surface pattern. (2) The microscopic peakto-
valley distances of surface protuberances and depressions.
Segregation:
(1) Nonuniform distribution of alloying elements, impurities, or microphases in
metals and alloys.
(2) A casting defect involving a concentration of alloying elements at specific regions, usually as a result of the primary crystallization of one phase with the subsequent concentration of other elements in the remaining liquid. Microsegregation refers to normal segregation on a microscopic scale in which material richer in an alloying element freezes in successive layers on the dendrites (coring) and in constituent network. Macrosegregation refers to gross differences in concentration (for example, from one area of a casting to another). Shear Bands:
(1) Bands of very high shear strain that are observed during rolling of sheet metal.
During rolling, these form at approximately 35o to the rolling plane, parallel to the transverse direction. They are independent of grain orientation and at high strain rates traverse the entire thickness of the rolled sheet. (2) Highly localized deformation zones in metals that are observed at very high strain rates, such as those produced by high velocity (100 to 3600 m/s, or 330 to 11,800 ft/s) projectile impacts or explosive rupture.
Shore Hardness:
A measure of the resistance of material to indentation by a spring-loaded indenter
during Sceleroscope hardness testing. The higher the number, the greater the resistance. Normally used for rubber materials.
Solidification:
The change in state from liquid to solid upon cooling through the melting
temperature or melting range.
Spheroidite:
A structure of global carbide in a matrix of soft ferrite.
Steel:
An iron-base alloy, malleable in some temperature ranges as initially cast,
containing manganese, usually carbon, and often other alloying elements. In carbon steel and low-alloy steel, the maximum carbon is about 2.0%; in high-alloy steel, about 2.5%.
The dividing line between low-alloy and high-alloy steels is generally regarded as being at about 5% metallic alloying elements.
Steel is said to be differentiated from two general classes of “irons”: the cast irons, on the high-carbon side, and the relatively pure irons such as ingot iron, carbonyl iron, and electrolytic iron, on the low-carbon side. In some steels containing extremely low carbon, the manganese content is the principal differentiating factor, steel usually containing at least 0.25% and ingot iron considerably less.
Strain Hardening:
An increase in hardness and strength of metals caused by plastic deformation at
temperatures below the re-crystallization range. Also known as work hardening.
Stress Relieving:
Heating to a suitable temperature, holding long enough to reduce residual stresses,
and then cooling slowly enough to minimize the development of new residual stresses.
Structure:
As applies to a crystal, the shape and size of the unit cell and the location of all
atoms within the unit cell. As applied to microstructure, the size, shape, and arrangement of phases.
Swage:
(1) The operation of reducing or changing the cross-section area of stock by the
fast impact of revolving dies. (2) The tapering of bar, rod, wire, or tubing by forging, hammering, or squeezing; reducing a section by progressively tapering lengthwise until the entire section attains the smaller dimension of the taper.
Tensile Strength:
In tensile testing, the ratio of maximum load to original cross-sectional area. Also
called ultimate strength.
Tensile Stress:
A stress that causes two parts of an elastic body, on either side of a typical stress plane, to pull apart.
Tension:
The force or load that produces elongation.
Tension Testing:
A method of determining the behavior of materials subjected to uniaxial loading,
which tends to stretch the material. A longitudinal specimen of known length and
diameter is gripped at both ends and stretched at a slow, controlled rate until rupture occurs. Also known as tensile testing.
Torsion:
(1) A twisting deformation of a solid or tubular body about an axis in which lines
that were initially parallel to the axis become helices. (2) A twisting action resulting in shear stresses and strains.
Transformation Temperature:
The temperature at which a change in phase occurs. This term is sometimes used
to denote the limiting temperature of a transformation range. The following symbols are used for irons and steel:
Accm. In hypereutectoid steel, the temperature at which a solution of cementite in austenite is completed during heating.
Ac1. The temperature at which austenite begins to form during heating.
Ac3. The temperature at which transformation of ferrite to austenite is completed during
heating.
Ac4. The temperature at which austenite transforms to delta ferrite during heating.
Aecm , Ae1 , Ae3 , Ae4. The temperatures of phase changes at equilibrium.
Arcm. In hypereutectoid steel, the temperature at which precipitation of cementite starts during cooling.
Ar1. The temperature at which transformation of austenite to ferrite or to ferrite plus
cementite is completed during cooling.
Ar3. The temperature at which austenite begins to transform to ferrite during cooling.
Ar4. The temperature at which delta ferrite transforms to austenite during cooling.
Ar-. The temperature at which transformation of austenite to pearlite starts during
cooling.
Mf. The temperature at which transformation of austenite to martensite is completed
during cooling.
Ms (or Ar.). The temperature at which transformation of austenite to martensite starts during cooling.
Note: All these changes, except formation of martensite, occur at lower temperatures
during cooling than during heating, and depend on the rate of change of temperature.
Transgranular:
Through or across crystals or grains. Also called intracrystalline or
transcrystalline.
Transition Phase:
A nonequilibrium state that appears in a chemical system in the course of
transformation between two equilibrium states.
Transverse Direction:
Literally, “across,” usually signifying a direction or plane perpendicular to the
direction of working. In rolled plate or sheet, the direction across the width is often called long transverse: the direction through the thickness, short transverse.
True Strain:
(1) The ratio of the change in dimension, resulting from a given load increment, to
the magnitude of the dimension immediately prior to applying the load increment. (2) In a body subjected to axial force, the natural logarithm of the ratio of the gage length at the moment of observation to the original gage length. Also known as natural strain.
True Stress:
The value obtained by dividing the load applied to a member at a given instant by
the cross-sectional area over which it acts.
Ultimate Strength:
The maximum stress (tensile, compressive, or shear) a material can sustain without
fracture; determined by dividing maximum load by the original cross-sectional area of the specimen. Also known as nominal strength or maximum strength.
Ultimate Tensile Strength:
The ultimate or final (highest) stress sustained by a specimen in a tension test.
Upset:
(1) The localized increase in cross-sectional area of a workpiece or weldment
resulting from the application of pressure during mechanical fabrication or welding.
(2) That portion of a welding cycle during which the cross-sectional area is increased by the application of pressure.
(3) Bulk deformation resulting from the application of pressure in welding. The upset may be measured as a percent increase in interfacial area, a reduction in length, or a percent reduction in thickness (for lap joints).
Upsetting:
The working of metal so that the cross-sectional area of a portion or all of the
stock is increased.
Vickers Hardness Number (HV):
A number related to the applied load and the surface area of the permanent
impression made by a square-based pyramidal diamond indenter having included face
angles of 136o, computed form:
HV= 2P sin a/2 = 1.8544P
d2 d2 where P is applied load (kgf), d is mean diagonal of the impression (mm), and is the face angle of the indenter (136o).
Vicker Hardness Test:
A microindentation hardness test employing a 136o diamond pyramid indenter
(Vickers) and variable load, enabling the use of one hardness scale for all ranges of hardness-from very soft lead to tungsten carbide. Also known as diamond pyramid
hardness test.
Weldability:
A Specific or relative measure of the ability of a material to be welded under a
given set of conditions. Implicit in this definition is the ability of the completed weldment to fulfill all functions for which the part was designed.
Yield:
(1) Evidence of plastic deformation in structural materials. Also known as plastic
flow or creep.
(2) The ratio of the number of acceptable items produced in a production run to the total number that were attempted to be produced.
(3) Comparison of casting weight to the total weight of metal poured into the mold.
Yield Point:
The first stress in a material, usually less than the maximum attainable stress, at
which an increase in strain occurs without an increase in stress. Only certain materialsthose which exhibit a localized, heterogeneous type of transition from elastic to plastic deformation-produce a yield point. If there is a decrease in stress after yielding, a distinction may be made between upper and lower yield points. The load at which a sudden drop in the flow curve occurs is called the upper yield point. The constant load shown on the flow curve is the lower yield point.
Yield Strength:
The stress at which a material exhibits a specified deviation from proportionality of stress and strain. An offset of 0.2% is used for many materials, particularly metals.
Yield Stress:
The stress level of highly ductile materials at which large strains take place without further increase in stress.
Youngs Modulus:
A term used synonymously with modulus of elasticity. The ratio of tensile or
compressive stresses to the resulting strain.
Saturday, October 23, 2010
how to determine the condition of the hardest working component of a hydraulic system - the pump
As a pump wears in service, internal leakage increases and therefore the percentage of flow available to do useful work (volumetric efficiency) decreases.
If volumetric efficiency falls below a level considered acceptable for the application, the pump will need to be overhauled.
In a condition-based maintenance environment, the decision to change-out the pump is often based on remaining bearing life or deterioration in volumetric efficiency, whichever occurs first.
Volumetric efficiency is the percentage of theoretical pump flow available to do useful work. It is calculated by dividing the pump's actual output in liters or gallons per minute by its theoretical output, expressed as a percentage. Actual output is determined using a flow-tester to load the pump and measure its flow rate.
Because internal leakage increases as operating pressure increases and fluid viscosity decreases, these variables should be stated when stating volumetric efficiency.
For example, a hydraulic pump with a theoretical output of 100 GPM, and an actual output of 94 GPM at 5000 PSI and 120 SUS is said to have a volumetric efficiency of 94% at 5000 PSI and 120 SUS.
When calculating the volumetric efficiency of a variable displacement pump, internal leakage must be expressed as a constant.
To understand why this is so, think of the various leakage paths within a hydraulic pump as fixed orifices. The rate of flow through an orifice is dependant on the diameter (and shape) of the orifice, the pressure drop across it and fluid viscosity.
This means that if these variables remain constant, the rate of internal leakage remains constant, independent of the pump's displacement.
If volumetric efficiency falls below a level considered acceptable for the application, the pump will need to be overhauled.
In a condition-based maintenance environment, the decision to change-out the pump is often based on remaining bearing life or deterioration in volumetric efficiency, whichever occurs first.
Volumetric efficiency is the percentage of theoretical pump flow available to do useful work. It is calculated by dividing the pump's actual output in liters or gallons per minute by its theoretical output, expressed as a percentage. Actual output is determined using a flow-tester to load the pump and measure its flow rate.
Because internal leakage increases as operating pressure increases and fluid viscosity decreases, these variables should be stated when stating volumetric efficiency.
For example, a hydraulic pump with a theoretical output of 100 GPM, and an actual output of 94 GPM at 5000 PSI and 120 SUS is said to have a volumetric efficiency of 94% at 5000 PSI and 120 SUS.
When calculating the volumetric efficiency of a variable displacement pump, internal leakage must be expressed as a constant.
To understand why this is so, think of the various leakage paths within a hydraulic pump as fixed orifices. The rate of flow through an orifice is dependant on the diameter (and shape) of the orifice, the pressure drop across it and fluid viscosity.
This means that if these variables remain constant, the rate of internal leakage remains constant, independent of the pump's displacement.
Thursday, October 21, 2010
Top 10 reasons why employees hate their boss
1) Incompetent and unacknowledging - Employees hate bosses who doesn't have the essential competitive skills but still scorns the work they do. Whether or not the boss is competitive, the employee really longs for his good work to be acknowledged and not to be treated as a 'piece of crap'.
2) Privacy Invasion - 'He always keep guard about what I do, constantly checks out on the office phone about what I am busy at (an indirect way to know whether I am on a call with any acquaintance) and one day even peeped through the door to see what I am doing. Now I even doubt whether he is watching me once I reach home' says Anamika (name changed to protect identity). Now that's a real bad boss.
3) The narcissist boss - Employees hate bosses who acts as the 'know it all', who thinks they are second to none, hears nothing until it directly benefits him and so self obsessed to be called in the informal way 'a narcissist glory monger'.
4) Personal Insults - Bosses who torture employees with personal insults rather than choosing to reproach on the basis of their work quickly gets in the hate list. Many employees have long stories to say about bosses who frequently torture them with comments about their attitude and discriminate them deliberately.
5) The angry 'yelling' boss - You are the boss, thumbs up. But how on earth could you yell at me like that. Employees at some point or other meet the unfortunate fate of being victim to their boss' wrath. Justifiable the reason may be, but you are in my hate list boss.
6) The 'opportunist' boss - Employees obviously develops a dislike to their boss who refuses to mind them. But one day the same boss who never acknowledged your presence comes to you, smiles at you and the next thing you know, you are on an extra shift with heavy workload. Dislikes turn to hate for such opportunist bosses.
7) The 'tensed' boss - Employees tend to hate bosses who are always tensed and want them to finish of the work in a hurry. "He is so tensed and rushes things as if his head is on fire. His tension is so contagious that even we get tensed in his presence" Rahul, a software employee.
8) Stealing credits - Employees feel cheated and hate their boss when he or she steals the credit of their work but never forgets to blame them if something goes wrong.
9) Lack of clarity and feedback - Employees hate bosses who don't brief them properly and keep the employees ignorant with any real feedback on their work. And worse, employees are blamed for something which in turn would be the result of void feedback.
10) Lack of rapport - Employees hate bosses who lacks mutual respect and always play bossy without any real interest in befriending the employees.
2) Privacy Invasion - 'He always keep guard about what I do, constantly checks out on the office phone about what I am busy at (an indirect way to know whether I am on a call with any acquaintance) and one day even peeped through the door to see what I am doing. Now I even doubt whether he is watching me once I reach home' says Anamika (name changed to protect identity). Now that's a real bad boss.
3) The narcissist boss - Employees hate bosses who acts as the 'know it all', who thinks they are second to none, hears nothing until it directly benefits him and so self obsessed to be called in the informal way 'a narcissist glory monger'.
4) Personal Insults - Bosses who torture employees with personal insults rather than choosing to reproach on the basis of their work quickly gets in the hate list. Many employees have long stories to say about bosses who frequently torture them with comments about their attitude and discriminate them deliberately.
5) The angry 'yelling' boss - You are the boss, thumbs up. But how on earth could you yell at me like that. Employees at some point or other meet the unfortunate fate of being victim to their boss' wrath. Justifiable the reason may be, but you are in my hate list boss.
6) The 'opportunist' boss - Employees obviously develops a dislike to their boss who refuses to mind them. But one day the same boss who never acknowledged your presence comes to you, smiles at you and the next thing you know, you are on an extra shift with heavy workload. Dislikes turn to hate for such opportunist bosses.
7) The 'tensed' boss - Employees tend to hate bosses who are always tensed and want them to finish of the work in a hurry. "He is so tensed and rushes things as if his head is on fire. His tension is so contagious that even we get tensed in his presence" Rahul, a software employee.
8) Stealing credits - Employees feel cheated and hate their boss when he or she steals the credit of their work but never forgets to blame them if something goes wrong.
9) Lack of clarity and feedback - Employees hate bosses who don't brief them properly and keep the employees ignorant with any real feedback on their work. And worse, employees are blamed for something which in turn would be the result of void feedback.
10) Lack of rapport - Employees hate bosses who lacks mutual respect and always play bossy without any real interest in befriending the employees.
Top 10 reasons why employees hate their boss
1) Incompetent and unacknowledging - Employees hate bosses who doesn't have the essential competitive skills but still scorns the work they do. Whether or not the boss is competitive, the employee really longs for his good work to be acknowledged and not to be treated as a 'piece of crap'.
2) Privacy Invasion - 'He always keep guard about what I do, constantly checks out on the office phone about what I am busy at (an indirect way to know whether I am on a call with any acquaintance) and one day even peeped through the door to see what I am doing. Now I even doubt whether he is watching me once I reach home' says Anamika (name changed to protect identity). Now that's a real bad boss.
3) The narcissist boss - Employees hate bosses who acts as the 'know it all', who thinks they are second to none, hears nothing until it directly benefits him and so self obsessed to be called in the informal way 'a narcissist glory monger'.
4) Personal Insults - Bosses who torture employees with personal insults rather than choosing to reproach on the basis of their work quickly gets in the hate list. Many employees have long stories to say about bosses who frequently torture them with comments about their attitude and discriminate them deliberately.
5) The angry 'yelling' boss - You are the boss, thumbs up. But how on earth could you yell at me like that. Employees at some point or other meet the unfortunate fate of being victim to their boss' wrath. Justifiable the reason may be, but you are in my hate list boss.
6) The 'opportunist' boss - Employees obviously develops a dislike to their boss who refuses to mind them. But one day the same boss who never acknowledged your presence comes to you, smiles at you and the next thing you know, you are on an extra shift with heavy workload. Dislikes turn to hate for such opportunist bosses.
7) The 'tensed' boss - Employees tend to hate bosses who are always tensed and want them to finish of the work in a hurry. "He is so tensed and rushes things as if his head is on fire. His tension is so contagious that even we get tensed in his presence" Rahul, a software employee.
8) Stealing credits - Employees feel cheated and hate their boss when he or she steals the credit of their work but never forgets to blame them if something goes wrong.
9) Lack of clarity and feedback - Employees hate bosses who don't brief them properly and keep the employees ignorant with any real feedback on their work. And worse, employees are blamed for something which in turn would be the result of void feedback.
10) Lack of rapport - Employees hate bosses who lacks mutual respect and always play bossy without any real interest in befriending the employees.
2) Privacy Invasion - 'He always keep guard about what I do, constantly checks out on the office phone about what I am busy at (an indirect way to know whether I am on a call with any acquaintance) and one day even peeped through the door to see what I am doing. Now I even doubt whether he is watching me once I reach home' says Anamika (name changed to protect identity). Now that's a real bad boss.
3) The narcissist boss - Employees hate bosses who acts as the 'know it all', who thinks they are second to none, hears nothing until it directly benefits him and so self obsessed to be called in the informal way 'a narcissist glory monger'.
4) Personal Insults - Bosses who torture employees with personal insults rather than choosing to reproach on the basis of their work quickly gets in the hate list. Many employees have long stories to say about bosses who frequently torture them with comments about their attitude and discriminate them deliberately.
5) The angry 'yelling' boss - You are the boss, thumbs up. But how on earth could you yell at me like that. Employees at some point or other meet the unfortunate fate of being victim to their boss' wrath. Justifiable the reason may be, but you are in my hate list boss.
6) The 'opportunist' boss - Employees obviously develops a dislike to their boss who refuses to mind them. But one day the same boss who never acknowledged your presence comes to you, smiles at you and the next thing you know, you are on an extra shift with heavy workload. Dislikes turn to hate for such opportunist bosses.
7) The 'tensed' boss - Employees tend to hate bosses who are always tensed and want them to finish of the work in a hurry. "He is so tensed and rushes things as if his head is on fire. His tension is so contagious that even we get tensed in his presence" Rahul, a software employee.
8) Stealing credits - Employees feel cheated and hate their boss when he or she steals the credit of their work but never forgets to blame them if something goes wrong.
9) Lack of clarity and feedback - Employees hate bosses who don't brief them properly and keep the employees ignorant with any real feedback on their work. And worse, employees are blamed for something which in turn would be the result of void feedback.
10) Lack of rapport - Employees hate bosses who lacks mutual respect and always play bossy without any real interest in befriending the employees.
Monday, October 18, 2010
Hydraulic troubleshooting
Check and eliminate the easy things first.
Now, in case you're thinking this advice is too obvious to be useful, consider this troubleshooting situation I was involved in recently:
The machine in question had a complex hydraulic system, the heart of which comprised two engines driving ten hydraulic pumps. Six of the pumps were variable displacement and four of these had electronic horsepower control.
The symptoms of the problem were slow cycle times in combination with lug-down of the engines (loss of engine rpm). The machine had just been fitted with a new set of pumps.
The diagnosis of the mechanic in charge was that the hydraulic system was tuned above the power curve of the engines, that is the hydraulics were demanding more power than the engines could produce, resulting in lug-down and therefore, slow cycle times.
The other possible explanation of course, was that the engines were not producing their rated horsepower.
Due to the complexity of the hydraulic system, I knew that it would take around four hours to run a complete system check and tune-up. So in order to eliminate the easy things first, when I arrived on site I inquired about the condition of the engines and their service history.
The mechanic in charge not only assured me that the engines were in top shape, he was adamant that this was a "hydraulic" problem.
Four hours later, after running a complete check of the hydraulic system without finding anything significant, I was not totally surprised that the problem remained unchanged.
After a lengthy discussion, I managed to convince the mechanic to change the fuel filters and air cleaner elements on both engines.
This fixed the problem. It turned out that a bad batch of fuel had caused premature clogging of the engine fuel filters, which were preventing the engines from developing their rated horsepower.
Had the relatively simple task of changing the engine fuel filters had been carried out when the problem was first noticed, an expensive service call and four hours of downtime could have been avoided.
The moral of this story and troubleshooting lesson is:
ALWAYS check and eliminate the easy things FIRST.
Now, in case you're thinking this advice is too obvious to be useful, consider this troubleshooting situation I was involved in recently:
The machine in question had a complex hydraulic system, the heart of which comprised two engines driving ten hydraulic pumps. Six of the pumps were variable displacement and four of these had electronic horsepower control.
The symptoms of the problem were slow cycle times in combination with lug-down of the engines (loss of engine rpm). The machine had just been fitted with a new set of pumps.
The diagnosis of the mechanic in charge was that the hydraulic system was tuned above the power curve of the engines, that is the hydraulics were demanding more power than the engines could produce, resulting in lug-down and therefore, slow cycle times.
The other possible explanation of course, was that the engines were not producing their rated horsepower.
Due to the complexity of the hydraulic system, I knew that it would take around four hours to run a complete system check and tune-up. So in order to eliminate the easy things first, when I arrived on site I inquired about the condition of the engines and their service history.
The mechanic in charge not only assured me that the engines were in top shape, he was adamant that this was a "hydraulic" problem.
Four hours later, after running a complete check of the hydraulic system without finding anything significant, I was not totally surprised that the problem remained unchanged.
After a lengthy discussion, I managed to convince the mechanic to change the fuel filters and air cleaner elements on both engines.
This fixed the problem. It turned out that a bad batch of fuel had caused premature clogging of the engine fuel filters, which were preventing the engines from developing their rated horsepower.
Had the relatively simple task of changing the engine fuel filters had been carried out when the problem was first noticed, an expensive service call and four hours of downtime could have been avoided.
The moral of this story and troubleshooting lesson is:
ALWAYS check and eliminate the easy things FIRST.
Time Management
Important Not Important
Urgent I II
Not Urgent III IV
This is a McFarlan’s grid of time management. One may expect about 50 – 75% tasks in III quadrant for better planning. High percentage is I quadrant shows a firefighting, resulting into fatigue, frustration. Quadrant II may indicate a mismatch in prioritization while quadrant IV may indicates recreational activities.
It's a new day and one is raring to go. Person leaves home with a clear work agenda outlined for the day. he gets to the office, and things don't work as smoothly. People inevitably fall prey to multiple distractions that consume time, energy and concentration.
Phone calls, text messages, e-mails and many more can be the reasons. Then there's the customer/ client crisis, co-workers who need help or just want to chat or emergency meetings that disturb schedule, traffic jams, rotational shifts and don't forget boss who needs updates on all the projects immediately.
One may end up wishing one has few extra hours in a day to complete the work? Here are a few pointers from professionals on how to make the most of work hours.
Get organized
This is the key to making time at the office more productive. If one returns from a meeting to find extra files, letters and documents all over the desk and even on the chair? Instead of following own schedule, he gets distracted by someone else's priorities.
One important part of getting organized is to maintain a clearly designated ‘In basket’ at the desk so that people do not dump files / documents on desk randomly.
Once there is ‘To do’ list for the day figured out, check on ‘In basket’ to know what needs to be done pronto and what can wait.
One may find it helps to take print-outs of important tasks to be performed and pinning them on softboard. Setting reminders on phone can help to as does maintaining an organiser or diary."
Meetings are necessary (although often they can be quite unproductive). Planning the time and venue for the next meeting during the current one will save time coordinating for the next. Check if team meeting is out of necessity or simply habit.
Un-clutter schedule. Establish an agenda for important meetings and distribute it to all the participants a few hours before the meeting. Stay on track, start and end on time. If anybody’s presence is not essential for the entire meeting, ask privately in advance if it might be appropriate for that person to excuse himself early.
One of the thumb rules may be to invite those for the meeting who can contribute to at least 50 per cent of the items on the agenda and discuss sensitive issues with the key participants before the meeting. The effectiveness of a meeting diminishes with groups larger than eight to ten so watch out for group size.
Choose your tasks carefully
Make sure that the work (and the time put in) adds value to the organisation and that it makes the best use of one’s skills.
Ask a simple question, "Will this advance my career within the company?" and "Will I able to do justice to this assignment?" before one decides to sit on a committee or take on an additional project.
One may earn a lot more respect by teaming up with a colleague whose expertise complements than by taking on additional work on own, overburdening and burning out.
Few people may like to finish the uncomplicated tasks at the beginning of the day. It saves energy and interest for the rest of the day for tasks that will need more concentration.
This is perhaps the most cliched, yet perhaps the most important and most under-utilised.
Create and maintain a ‘To do’ list at all times and make it a habit to update it on a continuous basis. A ‘To do’ list used well can be extremely effective. In addition to scheduling and planning, make a daily ‘To-do’ list that can include short-term and long-term goals. There's nothing more satisfying than crossing off another task that has been accomplished.
Include urgent and non-urgent items so one will never forget or overlook anything. Carry list ith you at all times and break down projects and assignments into specific action points. For instance, instead of noting 'Prepare the sales report', one may write
• Research sales trends for last quarter
• Review related files
• Assess current sales performance
• Meet with sales executives for feedback
Prioritise ‘To-do’ items and assign each task a 1, 2 or 3 rating. Items marked '1' are important tasks that must get done right away. '2' items are important, but not as important as '1' items. '3' items are things that need to get done at some point, but there's no rush."
Once ratings are assigned to each task, re-write ‘To-do’ list with all the '1' items on top (in order of importance), then the '2' and '3' items. Complete the '1' items first." Reminders on the computer and phone have become a way of life at the office, but one needs to stick to them for them to be effective.
This may seem obvious, but think of how many times one has put off an important (sometimes unpleasant) task so that one may call a friend, chat or do something else that really didn't need to happen at that time.
One may be perceived as a workaholic because he tracks the time given to friends. It is sometimes embarrassing but saves a lot of personal time."
Club similar activities together
Make all phone calls at one go. Check all e-mail at once. Transitioning from one type of activity to another takes time, so group like ‘To-do’ items together and complete them at a designated time.
Don't overfill the 24 hours that one has in a day. Instead maximise them by becoming aware of how to spend a day. If one maintains a routine, create shortcuts and use time wisely. One can get everything done... with time to spare.
Urgent I II
Not Urgent III IV
This is a McFarlan’s grid of time management. One may expect about 50 – 75% tasks in III quadrant for better planning. High percentage is I quadrant shows a firefighting, resulting into fatigue, frustration. Quadrant II may indicate a mismatch in prioritization while quadrant IV may indicates recreational activities.
It's a new day and one is raring to go. Person leaves home with a clear work agenda outlined for the day. he gets to the office, and things don't work as smoothly. People inevitably fall prey to multiple distractions that consume time, energy and concentration.
Phone calls, text messages, e-mails and many more can be the reasons. Then there's the customer/ client crisis, co-workers who need help or just want to chat or emergency meetings that disturb schedule, traffic jams, rotational shifts and don't forget boss who needs updates on all the projects immediately.
One may end up wishing one has few extra hours in a day to complete the work? Here are a few pointers from professionals on how to make the most of work hours.
Get organized
This is the key to making time at the office more productive. If one returns from a meeting to find extra files, letters and documents all over the desk and even on the chair? Instead of following own schedule, he gets distracted by someone else's priorities.
One important part of getting organized is to maintain a clearly designated ‘In basket’ at the desk so that people do not dump files / documents on desk randomly.
Once there is ‘To do’ list for the day figured out, check on ‘In basket’ to know what needs to be done pronto and what can wait.
One may find it helps to take print-outs of important tasks to be performed and pinning them on softboard. Setting reminders on phone can help to as does maintaining an organiser or diary."
Meetings are necessary (although often they can be quite unproductive). Planning the time and venue for the next meeting during the current one will save time coordinating for the next. Check if team meeting is out of necessity or simply habit.
Un-clutter schedule. Establish an agenda for important meetings and distribute it to all the participants a few hours before the meeting. Stay on track, start and end on time. If anybody’s presence is not essential for the entire meeting, ask privately in advance if it might be appropriate for that person to excuse himself early.
One of the thumb rules may be to invite those for the meeting who can contribute to at least 50 per cent of the items on the agenda and discuss sensitive issues with the key participants before the meeting. The effectiveness of a meeting diminishes with groups larger than eight to ten so watch out for group size.
Choose your tasks carefully
Make sure that the work (and the time put in) adds value to the organisation and that it makes the best use of one’s skills.
Ask a simple question, "Will this advance my career within the company?" and "Will I able to do justice to this assignment?" before one decides to sit on a committee or take on an additional project.
One may earn a lot more respect by teaming up with a colleague whose expertise complements than by taking on additional work on own, overburdening and burning out.
Few people may like to finish the uncomplicated tasks at the beginning of the day. It saves energy and interest for the rest of the day for tasks that will need more concentration.
This is perhaps the most cliched, yet perhaps the most important and most under-utilised.
Create and maintain a ‘To do’ list at all times and make it a habit to update it on a continuous basis. A ‘To do’ list used well can be extremely effective. In addition to scheduling and planning, make a daily ‘To-do’ list that can include short-term and long-term goals. There's nothing more satisfying than crossing off another task that has been accomplished.
Include urgent and non-urgent items so one will never forget or overlook anything. Carry list ith you at all times and break down projects and assignments into specific action points. For instance, instead of noting 'Prepare the sales report', one may write
• Research sales trends for last quarter
• Review related files
• Assess current sales performance
• Meet with sales executives for feedback
Prioritise ‘To-do’ items and assign each task a 1, 2 or 3 rating. Items marked '1' are important tasks that must get done right away. '2' items are important, but not as important as '1' items. '3' items are things that need to get done at some point, but there's no rush."
Once ratings are assigned to each task, re-write ‘To-do’ list with all the '1' items on top (in order of importance), then the '2' and '3' items. Complete the '1' items first." Reminders on the computer and phone have become a way of life at the office, but one needs to stick to them for them to be effective.
This may seem obvious, but think of how many times one has put off an important (sometimes unpleasant) task so that one may call a friend, chat or do something else that really didn't need to happen at that time.
One may be perceived as a workaholic because he tracks the time given to friends. It is sometimes embarrassing but saves a lot of personal time."
Club similar activities together
Make all phone calls at one go. Check all e-mail at once. Transitioning from one type of activity to another takes time, so group like ‘To-do’ items together and complete them at a designated time.
Don't overfill the 24 hours that one has in a day. Instead maximise them by becoming aware of how to spend a day. If one maintains a routine, create shortcuts and use time wisely. One can get everything done... with time to spare.
Saturday, October 2, 2010
Beginner’s Guide to Finding the Right Outsourcing IT Options
Beginner’s-Guide
The prime aim of Outsourcing IT for most of us is to increase the profit without compromising with defined parameters of your clients.
You too might be looking for best options for project outsourcing. Having so many out sourcing options, how you can be sure of selecting the best to get the end results as per your expectations.
Certainly, selecting the costliest option is not the guarantee of getting the best. So, ‘how to start’ is initial stage problem that is faced even by experienced outsourcers.
The best solution of this problem is ‘self-assessment’ prior to go for outsourcing. Self assessment exercise, ‘what and how to outsource’, helps you to identify your exact requirement. It not only cuts down the project cost but also makes whole outsourcing process smooth going.
Following 4 options your outsourcing IT may have will help you in deciding ‘what and how’ to outsource.
1. Staff Augmentation:
Staff Augmentation is the basic model for outsourcing. It is the best choice if you are less experienced in outsourcing tasks because it doesn’t affect the existing ownership and control over the business.
Under this option, you ask the service provider to provide specific skilled supporting staff as a low cost supplement skill option. Here, service providers can’t be held responsible for the end results because the provided professionals work under your commands.
Pros: Certain $$$$ of cost flexibility for a long duration.
Cons: Ambiguity around Outsourcing vendor quality resources
2. Out-Tasking:
Out-Tasking option of project outsourcing makes the service provider responsible for specific tasks. Under this option, overall control of the project remains unshared with Outsourcing service provider while the providers perform some specific tasks that was provided to them e.g. Design / Programming specified module / Testing – and do not take on end to end Service Level Agreements (SLAs)
Out-tasking is a good choice to accomplish short term tasks especially if you identify existing talent hub incapable to perform as per the project requirements.
Pros: Specific task level quality profiles can be acquired outsourced.
Cons: Not a right collaboration as the Outsourcing vendor takes on partial risks.
3. Project Based:
This is one step advanced Out-Tasking option for outsourcing a project. Service providers are given complete responsibility for a project operation. The accountability for the project level but not for business level outcomes lies with service provider.
Service Level Agreement (SLA) is determined upfront – before projects are outsourced. Vendors are held accountable to these service levels. You as an outsourcer monitor the project progress closely.
Pros: Great model where Outsourcing vendors share the risks and rewards.
Cons: Demands better Biz-IT arrangement while gathering project requirements.
4. Managed Services:
Larger corporations often use an end-to-end solution approach, where all of their IT needs- ranging from ERP business solutions across business locations, maintenance of consolidated business applications or support IT infrastructure.
If you are a matured outsourcer and have good data base of service providers with whom you have worked already, Managed Services outsourcing is the best option.
In a Managed Services Outsourcing approach, one Outsourcing vendor will either
(4.1) obtain on every viewpoint of the Outsourced work or
(4.2) enter into Service Level Agreements with other Outsourcing vendors to
Outline
As an outcome you get the benefit of having one of the following:
An integrated IT business solution provided by ONE Outsourcing vendor or Operational Service Level Agreements which are signed on by all Outsourcing vendors on how they will team up with each other
Pros: Dealing with just one Outsourcing vendor or have an integrated Outsourcing solution.
Cons: This is for a very large complex outsourcing business solution where there is a need to have on-site support for a few years.
Conclusion
So, selection of outsourcing option depends on Outsourcing maturity level, existing infrastructure and the nature of project.
Following a road map to migrate from one project outsourcing model to another is also a good option but every step should be taken with utmost care.
To make the project outsourcing affair more cost effective and result oriented, a visit to How to Negotiate with an Offshore Outsourcing Company May be very helpful.
Posted on October 2, 2010 by riken on http://blog.outsourcing-partners.com/2010/10/beginner%E2%80%99s-guide-to-finding-the-right-outsourcing-it-options/
The prime aim of Outsourcing IT for most of us is to increase the profit without compromising with defined parameters of your clients.
You too might be looking for best options for project outsourcing. Having so many out sourcing options, how you can be sure of selecting the best to get the end results as per your expectations.
Certainly, selecting the costliest option is not the guarantee of getting the best. So, ‘how to start’ is initial stage problem that is faced even by experienced outsourcers.
The best solution of this problem is ‘self-assessment’ prior to go for outsourcing. Self assessment exercise, ‘what and how to outsource’, helps you to identify your exact requirement. It not only cuts down the project cost but also makes whole outsourcing process smooth going.
Following 4 options your outsourcing IT may have will help you in deciding ‘what and how’ to outsource.
1. Staff Augmentation:
Staff Augmentation is the basic model for outsourcing. It is the best choice if you are less experienced in outsourcing tasks because it doesn’t affect the existing ownership and control over the business.
Under this option, you ask the service provider to provide specific skilled supporting staff as a low cost supplement skill option. Here, service providers can’t be held responsible for the end results because the provided professionals work under your commands.
Pros: Certain $$$$ of cost flexibility for a long duration.
Cons: Ambiguity around Outsourcing vendor quality resources
2. Out-Tasking:
Out-Tasking option of project outsourcing makes the service provider responsible for specific tasks. Under this option, overall control of the project remains unshared with Outsourcing service provider while the providers perform some specific tasks that was provided to them e.g. Design / Programming specified module / Testing – and do not take on end to end Service Level Agreements (SLAs)
Out-tasking is a good choice to accomplish short term tasks especially if you identify existing talent hub incapable to perform as per the project requirements.
Pros: Specific task level quality profiles can be acquired outsourced.
Cons: Not a right collaboration as the Outsourcing vendor takes on partial risks.
3. Project Based:
This is one step advanced Out-Tasking option for outsourcing a project. Service providers are given complete responsibility for a project operation. The accountability for the project level but not for business level outcomes lies with service provider.
Service Level Agreement (SLA) is determined upfront – before projects are outsourced. Vendors are held accountable to these service levels. You as an outsourcer monitor the project progress closely.
Pros: Great model where Outsourcing vendors share the risks and rewards.
Cons: Demands better Biz-IT arrangement while gathering project requirements.
4. Managed Services:
Larger corporations often use an end-to-end solution approach, where all of their IT needs- ranging from ERP business solutions across business locations, maintenance of consolidated business applications or support IT infrastructure.
If you are a matured outsourcer and have good data base of service providers with whom you have worked already, Managed Services outsourcing is the best option.
In a Managed Services Outsourcing approach, one Outsourcing vendor will either
(4.1) obtain on every viewpoint of the Outsourced work or
(4.2) enter into Service Level Agreements with other Outsourcing vendors to
Outline
As an outcome you get the benefit of having one of the following:
An integrated IT business solution provided by ONE Outsourcing vendor or Operational Service Level Agreements which are signed on by all Outsourcing vendors on how they will team up with each other
Pros: Dealing with just one Outsourcing vendor or have an integrated Outsourcing solution.
Cons: This is for a very large complex outsourcing business solution where there is a need to have on-site support for a few years.
Conclusion
So, selection of outsourcing option depends on Outsourcing maturity level, existing infrastructure and the nature of project.
Following a road map to migrate from one project outsourcing model to another is also a good option but every step should be taken with utmost care.
To make the project outsourcing affair more cost effective and result oriented, a visit to How to Negotiate with an Offshore Outsourcing Company May be very helpful.
Posted on October 2, 2010 by riken on http://blog.outsourcing-partners.com/2010/10/beginner%E2%80%99s-guide-to-finding-the-right-outsourcing-it-options/
GENERAL PROCEDURE OF FINITE ELEMENT METHOD
GENERAL PROCEDURE OF
FINITE ELEMENT METHOD
As stated in the previous chapter, following are the basics steps involved in the FEA
1.DISCRITISATION OF THE DOMAIN
The discretization of the domain or solution region into sub-regions(finite elements) is the first step in the finite element method .The process of discretization is essentially an exercise of an engineering judgement.The shapes,sizes,number and configuration of the body have to be chosen carefully so that ,the computational efforts needed for the solution are minimized.
In this step, following factors are considered chiefly:
BASIC ELEMENT SHAPE-
Mostly ,choice of the type of element is dictated by the geometry of the body and the number of independent spatial co-ordinates necessary to describe the system .The element may be one ,two and three dimensional
When the geometry, material properties and other parameters (stress, displacement, pressure and temperature) can be described in terms of only one spatial co-ordinate,we can use the one dimensional element . Although this element has a cross-sectional area ,it is generally shown schematically as a line segment .When configuration and other details of the problem can be described in terms of two independent spatial co-ordinates ,we can use the two dimensional elements.The basics element useful for the two dimensional analysis is the triangular element.Rectangular and parallelogram shaped elements or quadrilateral (combination of two or four triangular elements) element can also be used .
If the geometary,material properties and other parameters of the body can be described by three independent spatial co-ordinates, we can idealize the body by using three dimensional element.Tetrahedron element is the basics three dimensional element.Hexahedrogon can also be used advantageously.
The problems that possess axial symmetry like pistons, storage tanks, valves, rocket nozzles fall into this category. For the discritisation of the problem involving curved geometries finite elements with curved size are useful. The ability to model curved boundaries has been made possible by the addition of mid-side nodes.
Finite element with straight sides is known as linear elements, while those with curved sides are called higher order elements.
2.DISCRITISATION PROCESS-
(a) TYPE OF ELEMENTS- The type of element to be used will be evident from the physical problem itself ,
For example- If the problem involves analysis of a truss structure under a given set of load condition , the type of elements to be used for idealization is line or bar element
Similarly for stress analysis of short beam the elements are three-dimensional solid elements. Generally while selecting elements, following factors are considered : Degree of freedom needed ,ease with which the necessary equations can be modeled without approximation .
In certain problems where the body cannot be represented as assemblage of only one type of elements , we have to use two or more types of elements for idealization , for example : Aircraft wing analysis (fig) Here for the covers , rectangular shear panels are used and frame elements are used for flanges.
(b) SIZE OF ELEMENT:
Generally, small sized elements gives accurate final solution but here the computational time increases. Sometimes, we may have to use elements of different sizes in the same body. In the stress analysis of a plate with hole stress concentration is expected around hole. Therefore, finer mesh or smaller sized elements are used around the hole as compared to far away places.
Another characteristic, which is related to the size of element and affects the final solution, is ‘Aspect ratio’. Aspect ratio decreases shape of the element in the assemblage of elements. For two dimensional elements the aspect ratio is taken as the ratio of the largest dimension of element to the smallest dimension .Element with an aspect ratio nearly unity generally yield best results.
(c)LOCATION OF NODES:
If the body has no abrupt changes in the geometry ,material properties and external conditions (load,temperature etc.) the body can be divided into equal sub- divisions and hence spacing of the nodes can be uniform.On the other hand ,if there are any discontinuities in the problem ,nodes have to be introduced at these discontinuities .
In other words where there is a possibility of stress concentration ,node is introduced at that point on the body .
(d)NUMBER OF ELEMENTS:
The no elements to be chosen for idealization is related to accuracy desired,size of elements and the no. of degree of freedom involved .Although an increase in no. of elements generally means more accurate results,for any given problem,there will be a certain no. of elements beyond which the accuracy can not be improved any significant amount .If we increase no. of elements beyond this limits ,unnecessarily computation
time goes on increasing .Also we may not be able to the resulting matrices in the available computer memory .
(e)SIMPLIFICATION OFFERED BY PHYSICAL CONFIGURATION OF THE BODY:
If the configuration of the body as well as external conditions are symmetric
,we may only half of the body for the finite element idealization .The symmetry conditions , however have to be incorporated in the solution procedure .In certain cases,depending upon physical configuration of the body ,one quarter of the plate can be considered for analysis .
(f)FINITE REPRESENTATION OF INFINITE BODIES:
In some cases, where the boundaries of the body are not clearly defined,
For example dam, unit slice of the dam be considered for idealization and analyzed as a plane stain problem.
(g)NODE NUMBERING SCHEME:
Bandwidth (B)=(Maximum difference between the numbered degrees of freedom at the ends of any number +1)
This can be generalized as,:
Bandwidth (B)=(D+1)*f
Where,
D=maximum largest difference in the nodes numbers occurring for all elements of assemblage,
f=degrees of freedom at each node.
For good results ,bandwidth should be minimum and this can be achieved by minimizing D,which in turn can be achieved by numbering the nodes across the shortest dimension of the body .
The advances in the finite element analysis of large practical system have been made possible largely due to the banded nature of matrices .Further ,since most of the matrices .Further ,since most of the matrices involved are symmetric ,the demands on the computer storage can be substantially reduced by storing only the elements involved in the half bandwidth instead of storing whole matrix .
If we can minimize the bandwidth , the storage requirements as well as solution time can also be minimized .Since degrees of freedom is generally fixed for any given type of problem, bandwidth can be minimized by proper numbering scheme .
(2)INTERPOLATION POLYNOMIALS:
After dividing the body into elements ,the next step is to approximate the solution over each subregion by a simple function .The functions used to represent the behavior of the solution within an element are called interpolation functions/approximating functions or interpolating models .Mostly ,polynomial type of interpolation functions have been used because of following reasons:
a)It is to formulate and computerize the finite elements equations with polynomials type of interpolation functions.
b)It is possible to improve the accuracy of the results by increasing the order of the polynomials .Generally polynomials of infinite order corresponds to exact solution ,but in practice we take finite order polynomials as an approximation.
FINITE ELEMENT METHOD
As stated in the previous chapter, following are the basics steps involved in the FEA
1.DISCRITISATION OF THE DOMAIN
The discretization of the domain or solution region into sub-regions(finite elements) is the first step in the finite element method .The process of discretization is essentially an exercise of an engineering judgement.The shapes,sizes,number and configuration of the body have to be chosen carefully so that ,the computational efforts needed for the solution are minimized.
In this step, following factors are considered chiefly:
BASIC ELEMENT SHAPE-
Mostly ,choice of the type of element is dictated by the geometry of the body and the number of independent spatial co-ordinates necessary to describe the system .The element may be one ,two and three dimensional
When the geometry, material properties and other parameters (stress, displacement, pressure and temperature) can be described in terms of only one spatial co-ordinate,we can use the one dimensional element . Although this element has a cross-sectional area ,it is generally shown schematically as a line segment .When configuration and other details of the problem can be described in terms of two independent spatial co-ordinates ,we can use the two dimensional elements.The basics element useful for the two dimensional analysis is the triangular element.Rectangular and parallelogram shaped elements or quadrilateral (combination of two or four triangular elements) element can also be used .
If the geometary,material properties and other parameters of the body can be described by three independent spatial co-ordinates, we can idealize the body by using three dimensional element.Tetrahedron element is the basics three dimensional element.Hexahedrogon can also be used advantageously.
The problems that possess axial symmetry like pistons, storage tanks, valves, rocket nozzles fall into this category. For the discritisation of the problem involving curved geometries finite elements with curved size are useful. The ability to model curved boundaries has been made possible by the addition of mid-side nodes.
Finite element with straight sides is known as linear elements, while those with curved sides are called higher order elements.
2.DISCRITISATION PROCESS-
(a) TYPE OF ELEMENTS- The type of element to be used will be evident from the physical problem itself ,
For example- If the problem involves analysis of a truss structure under a given set of load condition , the type of elements to be used for idealization is line or bar element
Similarly for stress analysis of short beam the elements are three-dimensional solid elements. Generally while selecting elements, following factors are considered : Degree of freedom needed ,ease with which the necessary equations can be modeled without approximation .
In certain problems where the body cannot be represented as assemblage of only one type of elements , we have to use two or more types of elements for idealization , for example : Aircraft wing analysis (fig) Here for the covers , rectangular shear panels are used and frame elements are used for flanges.
(b) SIZE OF ELEMENT:
Generally, small sized elements gives accurate final solution but here the computational time increases. Sometimes, we may have to use elements of different sizes in the same body. In the stress analysis of a plate with hole stress concentration is expected around hole. Therefore, finer mesh or smaller sized elements are used around the hole as compared to far away places.
Another characteristic, which is related to the size of element and affects the final solution, is ‘Aspect ratio’. Aspect ratio decreases shape of the element in the assemblage of elements. For two dimensional elements the aspect ratio is taken as the ratio of the largest dimension of element to the smallest dimension .Element with an aspect ratio nearly unity generally yield best results.
(c)LOCATION OF NODES:
If the body has no abrupt changes in the geometry ,material properties and external conditions (load,temperature etc.) the body can be divided into equal sub- divisions and hence spacing of the nodes can be uniform.On the other hand ,if there are any discontinuities in the problem ,nodes have to be introduced at these discontinuities .
In other words where there is a possibility of stress concentration ,node is introduced at that point on the body .
(d)NUMBER OF ELEMENTS:
The no elements to be chosen for idealization is related to accuracy desired,size of elements and the no. of degree of freedom involved .Although an increase in no. of elements generally means more accurate results,for any given problem,there will be a certain no. of elements beyond which the accuracy can not be improved any significant amount .If we increase no. of elements beyond this limits ,unnecessarily computation
time goes on increasing .Also we may not be able to the resulting matrices in the available computer memory .
(e)SIMPLIFICATION OFFERED BY PHYSICAL CONFIGURATION OF THE BODY:
If the configuration of the body as well as external conditions are symmetric
,we may only half of the body for the finite element idealization .The symmetry conditions , however have to be incorporated in the solution procedure .In certain cases,depending upon physical configuration of the body ,one quarter of the plate can be considered for analysis .
(f)FINITE REPRESENTATION OF INFINITE BODIES:
In some cases, where the boundaries of the body are not clearly defined,
For example dam, unit slice of the dam be considered for idealization and analyzed as a plane stain problem.
(g)NODE NUMBERING SCHEME:
Bandwidth (B)=(Maximum difference between the numbered degrees of freedom at the ends of any number +1)
This can be generalized as,:
Bandwidth (B)=(D+1)*f
Where,
D=maximum largest difference in the nodes numbers occurring for all elements of assemblage,
f=degrees of freedom at each node.
For good results ,bandwidth should be minimum and this can be achieved by minimizing D,which in turn can be achieved by numbering the nodes across the shortest dimension of the body .
The advances in the finite element analysis of large practical system have been made possible largely due to the banded nature of matrices .Further ,since most of the matrices .Further ,since most of the matrices involved are symmetric ,the demands on the computer storage can be substantially reduced by storing only the elements involved in the half bandwidth instead of storing whole matrix .
If we can minimize the bandwidth , the storage requirements as well as solution time can also be minimized .Since degrees of freedom is generally fixed for any given type of problem, bandwidth can be minimized by proper numbering scheme .
(2)INTERPOLATION POLYNOMIALS:
After dividing the body into elements ,the next step is to approximate the solution over each subregion by a simple function .The functions used to represent the behavior of the solution within an element are called interpolation functions/approximating functions or interpolating models .Mostly ,polynomial type of interpolation functions have been used because of following reasons:
a)It is to formulate and computerize the finite elements equations with polynomials type of interpolation functions.
b)It is possible to improve the accuracy of the results by increasing the order of the polynomials .Generally polynomials of infinite order corresponds to exact solution ,but in practice we take finite order polynomials as an approximation.
GENERAL DESCRIPTION OF FINITE ELEMENT METHOD
In the finite element method ,the actual continuum or body of matter like solid ,liquid or gas is represented as an assemblage of sub-divisions called finite elements.These elements are considered to be interconnected at specified joints which are called ‘nodal points’ or nodes .The nodes usually lie on the elements boundaries where adjacent elements are considered to be connected .Since the actual variation of the field variable (displacements,stress,temperature,pressure,velocity) inside the continuum is not known ,we assume that ,the variation of the field variable inside a finite element can be approximated by a simple function .These approximating functions (are called interpolating models) are defined in terms of field variables at the nodes .When field equations for the whole continuum are written ,the new unknowns will be the nodal values of the field variable.
By solving the field equations, which are generally in the form of matrix equation, the nodal values of the field variables will be known. Once these are known, the approximating functions define the field variables throughout the assemblage of elements.
The solution of a general continuum problem by the FEM always follows an orderly step by step process as follows: -
STEP I: DESCRITISATION OF THE STRUCTURE
The continuum is separated by imaginary lines of surfaces into a number of finite elements .The number, type, size and the arrangements of the elements have to be decided.
STEP 2: SELECTION OF A PROPER INTERPOLATION OR DISPLACEMENT MODEL
Since the displacement solution of a complex structure under any specified load conditions cannot be predicted exactly, we assume some suitable solution within element to approximate the unknown solution.( The assumed solution must be simple from computational point of view.)
Step III : DERIVATION OF ELEMENT STIFFNESS MATRICES AND LOAD VECTORS
From the assumed displacement model, the stiffness matrix [ ke] and the load vector [ pe ], of element ‘e’ are to be derived by using either equilibrium conditions or a suitable variational principle.
Step IV : ASSEMBLAGE OF ELEMENT EQUATIONS TO OBTAIN THE OVERALL EQUILIBRIUM EQUATIONS
Since the structure is composed of several finite elements , the individual element stiffness matrices and load vectors are to be assembled in suitable manner and overall equilibrium equations have to be formulated as ,
[ K ] = p
where ,
[k] = assembled stiffness matrix ,
= Vector of nodal displacements ,
T = Vector of nodal forces for the complete structure.
Step V : SOLUTION FOR THE UNKNOWN NODAL DISPLACEMENTS
The overall equilibrium equations have to be modified to account for the boundary conditions of the problem. After the incorporation of the boundary condition , the equilibrium equation can be expressed as :
[ k ] = P
Step VI : COMPUTATION OF ELEMENT STRAINS AND STRESSES
From the known nodal displacements , element strains and stresses can be computed using equation of solid or structural mechanics.
The application of above 6 steps can be illustrated with the help of stepper bar problem.
In an equilibrium problem,we need to find the steady state displacement or stressed distribution if it is a solid mechanics problem,temperature or heat flux distribution if it is heat transfer problem and pressure or velocity distribution if it is fluid mechanics problem.
By solving the field equations, which are generally in the form of matrix equation, the nodal values of the field variables will be known. Once these are known, the approximating functions define the field variables throughout the assemblage of elements.
The solution of a general continuum problem by the FEM always follows an orderly step by step process as follows: -
STEP I: DESCRITISATION OF THE STRUCTURE
The continuum is separated by imaginary lines of surfaces into a number of finite elements .The number, type, size and the arrangements of the elements have to be decided.
STEP 2: SELECTION OF A PROPER INTERPOLATION OR DISPLACEMENT MODEL
Since the displacement solution of a complex structure under any specified load conditions cannot be predicted exactly, we assume some suitable solution within element to approximate the unknown solution.( The assumed solution must be simple from computational point of view.)
Step III : DERIVATION OF ELEMENT STIFFNESS MATRICES AND LOAD VECTORS
From the assumed displacement model, the stiffness matrix [ ke] and the load vector [ pe ], of element ‘e’ are to be derived by using either equilibrium conditions or a suitable variational principle.
Step IV : ASSEMBLAGE OF ELEMENT EQUATIONS TO OBTAIN THE OVERALL EQUILIBRIUM EQUATIONS
Since the structure is composed of several finite elements , the individual element stiffness matrices and load vectors are to be assembled in suitable manner and overall equilibrium equations have to be formulated as ,
[ K ] = p
where ,
[k] = assembled stiffness matrix ,
= Vector of nodal displacements ,
T = Vector of nodal forces for the complete structure.
Step V : SOLUTION FOR THE UNKNOWN NODAL DISPLACEMENTS
The overall equilibrium equations have to be modified to account for the boundary conditions of the problem. After the incorporation of the boundary condition , the equilibrium equation can be expressed as :
[ k ] = P
Step VI : COMPUTATION OF ELEMENT STRAINS AND STRESSES
From the known nodal displacements , element strains and stresses can be computed using equation of solid or structural mechanics.
The application of above 6 steps can be illustrated with the help of stepper bar problem.
In an equilibrium problem,we need to find the steady state displacement or stressed distribution if it is a solid mechanics problem,temperature or heat flux distribution if it is heat transfer problem and pressure or velocity distribution if it is fluid mechanics problem.
Finite Element Method
The limitations of human mind are such that it cannot grasp the behavior of its complex surrounding and creations in one operation. Thus the process of subdividing all systems into their individual components or elements, whose behavior is all readily understood and then rebuilding the original system from such components to study its behavior is a natural way in which the engineer, the scientist or even the economist Proceeds .
The finite element method is a numerical method, which can be used for the solution of complex engineering problems with accuracy acceptable to engineers.
In 1957 this method was first developed basically for the analysis of aircraft structures.
There after the usefulness of this method for various engineering problems were recognized .over the years ,the finite element technique has been so well developed that ,today it is considered to be one of the best method for solving a wide variety of practical problems efficiently.
One of the main reasons for the popularity of the method in different fields of engineering is that once a general computer program is written ,it can be used for the solution of any problem simply by changing the input data.
In FEM since the actual problem is replaced by a simpler one in finding the solution we will be able to find only an approximate solution rather than the exact solution .In most of the practical problems, the existing mathematical tools are not even able to find approximate solution of the problem .Thus, in the absence of any other convenient method to find even the approximate solution of a given problem, we have to prefer the FEM.
The digital computer provided a rapid means of performing many calculations involved in FEA. Alongwith the development of high speed computers, the application of the FEM also progressed at a very impressive rate.
The finite element method is a numerical method, which can be used for the solution of complex engineering problems with accuracy acceptable to engineers.
In 1957 this method was first developed basically for the analysis of aircraft structures.
There after the usefulness of this method for various engineering problems were recognized .over the years ,the finite element technique has been so well developed that ,today it is considered to be one of the best method for solving a wide variety of practical problems efficiently.
One of the main reasons for the popularity of the method in different fields of engineering is that once a general computer program is written ,it can be used for the solution of any problem simply by changing the input data.
In FEM since the actual problem is replaced by a simpler one in finding the solution we will be able to find only an approximate solution rather than the exact solution .In most of the practical problems, the existing mathematical tools are not even able to find approximate solution of the problem .Thus, in the absence of any other convenient method to find even the approximate solution of a given problem, we have to prefer the FEM.
The digital computer provided a rapid means of performing many calculations involved in FEA. Alongwith the development of high speed computers, the application of the FEM also progressed at a very impressive rate.
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