Glossary Compiled and revised by Debbie Aliya, Aliya Analytical, W.T. Becker, Consultant (University of Tennessee Retired), and roch Shipley, Packer Engineering Inc COMMUNICATION is often the key issue in practical failure analysis. Communication is required among specific parties who are trying to solve a problem. It is recognized that the exact definition of a particular term may be less important than conveying the concept that solves the problem. However, it is typical in failure analysis and problem solving to consult the literature(including Handbooks such as this one)or other people to find information on similar problems. Without clear communication and consistent terminology, one cannot know if the problems are really similar In failure analysis work, it is often not possible to pin down a particular damage sequence or root cause with complete certainty. However, if the work is performed in a professional manner, there is a good probability of identifying some helpful solutions to at least reduce the likelihood of recurrence. This glossary is intended to help promote clear thinking and useful failure analysis. The process of defining terms is useful to the parties involved in solving a failure analysis problem, in that it increases their own comprehension of the physical facts and also facilitates communication with the other parties who need to understand the results of the Investigation Strict use of proper terminology is critical to clear communication. Several organizations have compiled glossaries of terms used in failure analysis, including ASTM, SAE, and ASM International. In some cases(e. g ASTM), accepted definitions of terms is by consensus approval of a committee. In other instances(e.g, ASM), there is no formal approval procedure nor is there a committee responsible for terminology. As a result, there may be more than one common use of a specific term, and there may be more than one definition of a term The definitions used in the following glossary are not al ways consistent with those for the same terms found in the ASM Materials Engineering Dictionary (J.R. Davis, editor, ASM International, 1992) or in glossaries in other ASM Handbook volumes. The use of a term (e.g, corrosion fatigue) may change with time as understanding evolves. The definitions presented here are those used in this volume and reflect common and modern understanding of these terms as used in the literature and in reports by practicing failure analysts However, as in all communication, if the way in which a particular term is being used is not clear, the speaker or author should be asked for clarificati Several terms used in discussions of failure analysis can be confusing or interpreted variously by different persons. Cases in point include mode, stress cracking, ductile, brittle, and cleavage. An example of the evolution of definitions, as previously noted, is the term quasi-cleavage, which is truly a form of cleavage and a microscale fracture surface appearance of a quenched and tempered steel. The fracture surface is typically dominated by cleavage, but there are typically small patches of microvoid coalescence(MvC) present or thin ribbons of MVC contained in the fracture surface. As the patches of MVC increase, the fracture surface is more accurately described as(microscale) mixed cleavage and MVC. In a matrix dominated by cleavage, there is nothing"quasi"about the cleavage, because the term quasi implies something different than cleavage Sometimes a modifying adjective may considerably improve the clarity of the sentence in which it is used. For example, ductile can refer to both a process/mechanism at the microscale or an appearance at the macroscale The term mode is used in multiple ways: It is defined in ASTM E 1823 in terms of surface displacement of the crack tip created by various loading conditions. It is defined within ASME Failure Methods and Effects Analysis terminology, and there are some eight additional definitions in Webster's Unabridged Dictionary There are still more uses of the term, as in fracture mode, failure mode, and so on. These latter two terms are not in the ASM Materials Engineering Dictionary, nor are they in an ASTM glossary. Consequently, their use has no underlying, commonly accepted definition and should be avoided if possible Other examples of terms that may be misinterpreted include static fatigue and stress cracking. The compilers also discourage the use of terms that have been removed from glossaries created by consensus approval.An example is the term endurance limit. The endurance limit presumably indicates a threshold stress for infinite
Glossary Compiled and revised by Debbie Aliya, Aliya Analytical, W.T. Becker, Consultant (University of Tennessee, Retired), and Roch Shipley, Packer Engineering Inc. COMMUNICATION is often the key issue in practical failure analysis. Communication is required among specific parties who are trying to solve a problem. It is recognized that the exact definition of a particular term may be less important than conveying the concept that solves the problem. However, it is typical in failure analysis and problem solving to consult the literature (including Handbooks such as this one) or other people to find information on similar problems. Without clear communication and consistent terminology, one cannot know if the problems are really similar. In failure analysis work, it is often not possible to pin down a particular damage sequence or root cause with complete certainty. However, if the work is performed in a professional manner, there is a good probability of identifying some helpful solutions to at least reduce the likelihood of recurrence. This glossary is intended to help promote clear thinking and useful failure analysis. The process of defining terms is useful to the parties involved in solving a failure analysis problem, in that it increases their own comprehension of the physical facts and also facilitates communication with the other parties who need to understand the results of the investigation. Strict use of proper terminology is critical to clear communication. Several organizations have compiled glossaries of terms used in failure analysis, including ASTM, SAE, and ASM International. In some cases (e.g., ASTM), accepted definitions of terms is by consensus approval of a committee. In other instances (e.g., ASM), there is no formal approval procedure nor is there a committee responsible for terminology. As a result, there may be more than one common use of a specific term, and there may be more than one definition of a term. The definitions used in the following glossary are not always consistent with those for the same terms found in the ASM Materials Engineering Dictionary (J.R. Davis, editor, ASM International, 1992) or in glossaries in other ASM Handbook volumes. The use of a term (e.g., corrosion fatigue) may change with time as understanding evolves. The definitions presented here are those used in this Volume and reflect common and modern understanding of these terms as used in the literature and in reports by practicing failure analysts. However, as in all communication, if the way in which a particular term is being used is not clear, the speaker or author should be asked for clarification. Several terms used in discussions of failure analysis can be confusing or interpreted variously by different persons. Cases in point include mode, stress cracking, ductile, brittle, and cleavage. An example of the evolution of definitions, as previously noted, is the term quasi-cleavage, which is truly a form of cleavage and a microscale fracture surface appearance of a quenched and tempered steel. The fracture surface is typically dominated by cleavage, but there are typically small patches of microvoid coalescence (MVC) present or thin ribbons of MVC contained in the fracture surface. As the patches of MVC increase, the fracture surface is more accurately described as (microscale) mixed cleavage and MVC. In a matrix dominated by cleavage, there is nothing “quasi” about the cleavage, because the term quasi implies something different than cleavage. Sometimes a modifying adjective may considerably improve the clarity of the sentence in which it is used. For example, ductile can refer to both a process/mechanism at the microscale or an appearance at the macroscale. The term mode is used in multiple ways: It is defined in ASTM E 1823 in terms of surface displacement of the crack tip created by various loading conditions. It is defined within ASME Failure Methods and Effects Analysis terminology, and there are some eight additional definitions in Webster's Unabridged Dictionary. There are still more uses of the term, as in fracture mode, failure mode, and so on. These latter two terms are not in the ASM Materials Engineering Dictionary, nor are they in an ASTM glossary. Consequently, their use has no underlying, commonly accepted definition and should be avoided if possible. Other examples of terms that may be misinterpreted include static fatigue and stress cracking. The compilers also discourage the use of terms that have been removed from glossaries created by consensus approval. An example is the term endurance limit. The endurance limit presumably indicates a threshold stress for infinite
life in cyclic loading. It appears in S-N data for materials that strain age and is therefore associated with a dislocation-interstitial pinning mechanism. If some event occurs to cause depinning(say, an increased stress),a new saturation stress is obtained that is the endurance limit is changed. The term endurance limit is no longer contained in a standard glossary of terms used in fracture and fatigue(ASTM E 1823) There are a group of terms used to describe deviations from ideality and that are in some instances the technical root cause for failure. They include imperfection, discontinuity, defect and root cause. In some instances these terms are used interchangeably by some writers, and in other cases clear distinctions are made. In some instances, specific terms have been defined by legal jurisdictions. The failure analyst should consider the legal implication of his terminology. As noted, the courts have defined the meanings of certain words, and these meanings may not correspond to what the analyst intends. Furthermore, various courts may not be consistent For example, some metallurgists have examined a fracture surface and identified a defect at the fracture origin By this they mean nothing more than a discontinuity and perhaps a minute discontinuity. However, within a legal context, the identification of a defect suggests a defective component, legal liability for the manufacturer, and a possible need for a recall or other corrective action The definition of defect herein is based on deviation from a specification or a component being unfit for its intended purpose. An actual or perceived failure does not automatically mean there is a defect. Even if there is a defect, that condition may or may not relate to the failure. It is believed this framework provides a rational method for deciding if there is, in fact, a defect. However, it does not eliminate all controversy as specifications may or may not be clear, appropriate, and up-to-date. There may also be disagreement regarding the intended purpose of a component. a discussion on this matter from a legal perspective is in two references: (a) Asperger, J.J.,"Legal Definition of a Product Failure: What the Law Requires of the Designer and the Manufacturer, Failure Prevention Through Education, Getting to the root Cause, Conference Proceedings, ASM International, May 2000, and(b)"Product Liability and Design""in this Volume of the ASM Handbook. 475° C embrittlement Embrittlement of ferritic and semiferritic steels containing more than 13% Cr that occurs when they are held or slowly cooled through the 400 to 500C (750 to 930F) temperature range. Embrittlement is presumed to be due to the grain-boundary precipitation of a chromium-rich phase together with the creation of a precipitate-free zone(PFZ) adjacent to the grain boundary. Because the precipitation reates a PFZ, fracture is likely to be intergranula 500 to 700C embrittlement Embrittlement that occurs when high-alloy steels(e.g, hot work steels and high-speed steels)are cooled to form martensite and are subsequently tempered or slowly cooled through the 500 to 700C(930 to 1290F)temperature range. Tempering results in a fine dispersion of carbides. A small increase in hardness is associated with the embrittlement abrasion The process of grinding or wearing away through the use of abrasives; a roughening or scratching of a surface due to abrasive wear abrasive wear The removal of material from a surface when hard particles slide or roll across the surface under pressure. The particles may be loose or may be part of another surface in contact with the surface being abraded. Compare with adhesive wear adhesive wear The removal or displacement of material from a surface by the welding together and subsequent shearing of minute areas of two surfaces that slide across each other under pressure. Compare with brasive wear diabatic Occurring without loss or gain of heat in the system, which may result in a local temperature increase or decrease. Adiabatic conditions differ from isothermal conditions(under which the temperature remains constant) diabatic shear bands Thefileisdownloadedfromwww.bzfxw.com
life in cyclic loading. It appears in S-N data for materials that strain age and is therefore associated with a dislocation-interstitial pinning mechanism. If some event occurs to cause depinning (say, an increased stress), a new saturation stress is obtained; that is, the endurance limit is changed. The term endurance limit is no longer contained in a standard glossary of terms used in fracture and fatigue (ASTM E 1823). There are a group of terms used to describe deviations from ideality and that are in some instances the technical root cause for failure. They include imperfection, discontinuity, defect and root cause. In some instances these terms are used interchangeably by some writers, and in other cases clear distinctions are made. In some instances, specific terms have been defined by legal jurisdictions. The failure analyst should consider the legal implication of his terminology. As noted, the courts have defined the meanings of certain words, and these meanings may not correspond to what the analyst intends. Furthermore, various courts may not be consistent. For example, some metallurgists have examined a fracture surface and identified a defect at the fracture origin. By this they mean nothing more than a discontinuity and perhaps a minute discontinuity. However, within a legal context, the identification of a defect suggests a defective component, legal liability for the manufacturer, and a possible need for a recall or other corrective action. The definition of defect herein is based on deviation from a specification or a component being unfit for its intended purpose. An actual or perceived failure does not automatically mean there is a defect. Even if there is a defect, that condition may or may not relate to the failure. It is believed this framework provides a rational method for deciding if there is, in fact, a defect. However, it does not eliminate all controversy as specifications may or may not be clear, appropriate, and up-to-date. There may also be disagreement regarding the intended purpose of a component. A discussion on this matter from a legal perspective is in two references: (a) Asperger, J.J., “Legal Definition of a Product Failure: What the Law Requires of the Designer and the Manufacturer,” Failure Prevention Through Education, Getting to the Root Cause, Conference Proceedings, ASM International, May 2000, and (b) “Product Liability and Design” in this Volume of the ASM Handbook. 475 °C embrittlement Embrittlement of ferritic and semiferritic steels containing more than 13% Cr that occurs when they are held or slowly cooled through the 400 to 500 °C (750 to 930 °F) temperature range. Embrittlement is presumed to be due to the grain-boundary precipitation of a chromium-rich phase together with the creation of a precipitate-free zone (PFZ) adjacent to the grain boundary. Because the precipitation creates a PFZ, fracture is likely to be intergranular. 500 to 700 °C embrittlement Embrittlement that occurs when high-alloy steels (e.g., hot work steels and high-speed steels) are cooled to form martensite and are subsequently tempered or slowly cooled through the 500 to 700 °C (930 to 1290 °F) temperature range. Tempering results in a fine dispersion of carbides. A small increase in hardness is associated with the embrittlement. A abrasion The process of grinding or wearing away through the use of abrasives; a roughening or scratching of a surface due to abrasive wear. abrasive wear The removal of material from a surface when hard particles slide or roll across the surface under pressure. The particles may be loose or may be part of another surface in contact with the surface being abraded. Compare with adhesive wear. adhesive wear The removal or displacement of material from a surface by the welding together and subsequent shearing of minute areas of two surfaces that slide across each other under pressure. Compare with abrasive wear. adiabatic Occurring without loss or gain of heat in the system, which may result in a local temperature increase or decrease. Adiabatic conditions differ from isothermal conditions (under which the temperature remains constant). adiabatic shear bands The file is downloaded from www.bzfxw.com
Shear bands created under adiabatic conditions that is bands created under conditions of local heating created by high strain-rate deformation alligatoring allia the longitudinal splitting of flat slabs in a plane parallel to the rolled surface r skin See orange peel ambient Something usually used in relation to temperature, as "ambient temperature"surrounding a part or assembly. Often taken to mean comfortable indoor temperature annealing or growth twin a twin formed in a crystal or grain during recrystallization or, rarely, during solidification anode The electrode of an electrolytic cell at which oxidation occurs. Contrast with cathode arrest lines(marks) Lines or thin regions that appear on fracture surfaces. There are two types of arrest lines those created in monotonic loading and those from cyclic loading; the latter give information on the crack front position at a given point in time. Arrest lines in monotonic loading are created when the stored elastic strain energy cannot drive a crack completely across the remaining ligament. At the microscale, monotonic arrest lines are regions of microvoid coalescence. while the remainder of the fracture surface shows cleavage or quasi-cleavage cracking. Arrest lines in cyclic loading are created when the mponent remains in the unloaded condition for a time sufficiently long to crevice corrosion at the crack tip or for a sudden change in loading spectra. See also beach marks and rib mark asperity arial In tribology, a protuberance in the small-scale topographical irregularities of a solid surface Longitudinal, or parallel to the axis or centerline of a part. Usually refers to axial compression or axial tension or orientation of a metallographic or mechanical test coup axial strain The linear strain in a plane parallel to the longitudinal axis. Strain may be axial (tensile or compressive or shear. For constant-volume materials, axial strain in a direction is equal in magnitude to the areal strain on a plane whose normal is in the direction of axial strain. Axial strain is the integral of a change in length divided by a length If the length is considered to be a constant( typically the initial, i.e., gage length, Lo) dl L However. if the instantaneous length is considered See also shear strain B banded structur oo. Segregated structure consisting of alternating, nearly parallel bands of different composition and beach of primary flow in hot working but is often caused by conditions present when the material is cas ection bly microstructure(as in steels with pearlite banding). Banding is typically aligned in the dir
Shear bands created under adiabatic conditions; that is, bands created under conditions of local heating created by high strain-rate deformation. alligatoring The longitudinal splitting of flat slabs in a plane parallel to the rolled surface. alligator skin See orange peel. ambient Something usually used in relation to temperature, as “ambient temperature” surrounding a part or assembly. Often taken to mean “comfortable indoor temperature.” annealing or growth twin A twin formed in a crystal or grain during recrystallization or, rarely, during solidification. anode The electrode of an electrolytic cell at which oxidation occurs. Contrast with cathode. arrest lines (marks) Lines or thin regions that appear on fracture surfaces. There are two types of arrest lines: those created in monotonic loading and those from cyclic loading; the latter give information on the crack front position at a given point in time. Arrest lines in monotonic loading are created when the stored elastic strain energy cannot drive a crack completely across the remaining ligament. At the microscale, monotonic arrest lines are regions of microvoid coalescence, while the remainder of the fracture surface shows cleavage or quasi-cleavage cracking. Arrest lines in cyclic loading are created when the component remains in the unloaded condition for a time sufficiently long to cause crevice corrosion at the crack tip or for a sudden change in loading spectra. See also beach marks and rib mark. asperity In tribology, a protuberance in the small-scale topographical irregularities of a solid surface. axial Longitudinal, or parallel to the axis or centerline of a part. Usually refers to axial compression or axial tension or orientation of a metallographic or mechanical test coupon. axial strain The linear strain in a plane parallel to the longitudinal axis. Strain may be axial (tensile or compressive) or shear. For constant-volume materials, axial strain in a direction is equal in magnitude to the areal strain on a plane whose normal is in the direction of axial strain. Axial strain is the integral of a change in length divided by a length: dL L e = ò If the length is considered to be a constant (typically the initial, i.e., gage length, L0): 1 f o L f o o o L L L dL L L e æ ö - = = ç ÷ è ø ò However, if the instantaneous length is considered: ln f o L f L o dL L L L e æ ö = = ç ÷ è ø ò See also shear strain. B banded structure A segregated structure consisting of alternating, nearly parallel bands of different composition and possibly microstructure (as in steels with pearlite banding). Banding is typically aligned in the direction of primary flow in hot working but is often caused by conditions present when the material is cast. beach marks
Macroscopic(visible) progression marks on a fracture surface that indicate successive positions of the advancing crack front. The classic appearance is of irregular elliptical or semielliptical rings radiating outward from one or more origins. After some growth, the curvature may be lost or reversed as affected by component geometry. Curvature is an indication of the stress field and is also affected by biaxial loading conditions and the shape of the remaining uncracked ligament. Beach marks(also known as clamshell marks, tide marks, or arrest marks) are typically found on service fractures where the part is loaded randomly, intermittently, or with periodic variations in mean stress, alternating stress, or environmental conditions. Not to be confused with striation(a microscale feature) and monotonic crack arrest lines(which are macroscale and form by a different mechanism). Beach marks formed during intermittent loading are formed by crevice corrosion. In steels, this causes the progression mark to have a dark or black appearance bifurcation The separation of materials into two parts. See also crack bifurcation blue brittleness Brittleness exhibited by some steels after being heated to a temperature within the range of approximately 205 to 370C (400 to 700F), particularly if the steel is worked at the elevated temperature. Killed steels are virtually free of this kind of brittleness breaking stress See rupture stress 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, computed from 2P HB= D(D-√D2-d2 where P is applied load, kgf, D is diameter of ball, mm, and d is mean diameter of the impression, mm Brinell hardness test a test for determining the hardness of a material by forcing a hard steel or carbide ball of specified diameter into the surface of the material under a specified load for a specified time. The result is expressed as the brinell hardness number Brinell Damage to a solid bearing surface characterized by one or more plastically formed indentations brougH about by overload. This term is often applied in the case of rolling-element bearings. See also false Brinelling g brittle Permitting little or no plastic(permanent)deformation prior to fracture. The term is used at both the macroscale and microscale Contrast with ductile brittle crack propagation A sudden propagation of a crack with the absorption of no energy except that stored elastically in the body. Microscopic examination may reveal some plastic deformation that is not noticeable to the unaided eye. Contrast with ductile crack propagation brittle erosion behavior Erosion behavior having characteristic properties(e.g, little or no plastic flow, the formation of cracks) that can be associated with brittle fracture of the exposed surface. The maximum volume removal occurs at an angle near 90, in contrast to approximately 25 for ductile erosion behavior brittle fracture Separation of a solid accompanied by little or no macroscopic and/or microscopic plastic deformation Typically, brittle fracture occurs by rapid crack propagation, with less expenditure of energy than for ductile fracture. The term is used at the macroscale to describe appearance and at the microscale to describe both appearance and mechanisn brittleness The tendency of a material to fracture without first undergoing plastic deformation. Contrast with buckle Thefileisdownloadedfromwww.bzfxw.com
Macroscopic (visible) progression marks on a fracture surface that indicate successive positions of the advancing crack front. The classic appearance is of irregular elliptical or semielliptical rings radiating outward from one or more origins. After some growth, the curvature may be lost or reversed as affected by component geometry. Curvature is an indication of the stress field and is also affected by biaxial loading conditions and the shape of the remaining uncracked ligament. Beach marks (also known as clamshell marks, tide marks, or arrest marks) are typically found on service fractures where the part is loaded randomly, intermittently, or with periodic variations in mean stress, alternating stress, or environmental conditions. Not to be confused with striation (a microscale feature) and monotonic crack arrest lines (which are macroscale and form by a different mechanism). Beach marks formed during intermittent loading are formed by crevice corrosion. In steels, this causes the progression mark to have a dark or black appearance. bifurcation The separation of materials into two parts. See also crack bifurcation. blue brittleness Brittleness exhibited by some steels after being heated to a temperature within the range of approximately 205 to 370 °C (400 to 700 °F), particularly if the steel is worked at the elevated temperature. Killed steels are virtually free of this kind of brittleness. breaking stress See rupture stress. 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, computed from: ( ) 2 ² ² P HB p D D D d = - - where P is applied load, kgf; D is diameter of ball, mm; and d is mean diameter of the impression, mm. Brinell hardness test A test for determining the hardness of a material by forcing a hard steel or carbide ball of specified diameter into the surface of the material under a specified load for a specified time. The result is expressed as the Brinell hardness number. Brinelling Damage to a solid bearing surface characterized by one or more plastically formed indentations brought about by overload. This term is often applied in the case of rolling-element bearings. See also false Brinelling. brittle Permitting little or no plastic (permanent) deformation prior to fracture. The term is used at both the macroscale and microscale. Contrast with ductile. brittle crack propagation A sudden propagation of a crack with the absorption of no energy except that stored elastically in the body. Microscopic examination may reveal some plastic deformation that is not noticeable to the unaided eye. Contrast with ductile crack propagation. brittle erosion behavior Erosion behavior having characteristic properties (e.g., little or no plastic flow, the formation of cracks) that can be associated with brittle fracture of the exposed surface. The maximum volume removal occurs at an angle near 90°, in contrast to approximately 25° for ductile erosion behavior. brittle fracture Separation of a solid accompanied by little or no macroscopic and/or microscopic plastic deformation. Typically, brittle fracture occurs by rapid crack propagation, with less expenditure of energy than for ductile fracture. The term is used at the macroscale to describe appearance and at the microscale to describe both appearance and mechanism. brittleness The tendency of a material to fracture without first undergoing plastic deformation. Contrast with ductility. buckle The file is downloaded from www.bzfxw.com
(1)An indented valley in the surface of a sand casting due to expansion of the molding sand. (2)A local waviness in metal bar or sheet, usually transverse to the direction of rolling, caused by inconsistencies in the temperature or thickness of the material being rolled buckling A compression and torsion phenomenon that occurs when, after some critical level of load, a bulge, bend, bow, kink, or other wavy condition is produced in a beam, column, plate, bar, or sheet product The level of stress that causes buckling in a given component is dependent mainly on geometry and elastic modulus, but in some shapes, yield strength also has a strong influence on the resistence to bucklin bulk modulus See bulk modulus of elasticity bulk modulus of elasticity, K The measure of resistance to change in volume; the ratio of hydrostatic stress(om) to the corresponding unit change in volume(An). This elastic constant can be expressed by K △∥V△v∥vβ where K is the bulk modulus of elasticity, om is hydrostatic or mean normal stress, p is hydrostatic pressure, and B is compressibility. Also known as bulk modulus, hydrostatic modulus, and volumetric modulus of elasticity b (1)Permanently damaging a metal or alloy by heating to cause either incipient melting or intergranular oxidation. See also overheating and grain-boundary liquation. (2)In grinding, getting the work hot enough to cause discoloration or to change the microstructure by tempering or hardening carbon flotation Free grap that has separated from the molten iron in a cast iron. This imperfection tends to occur at the upper surfaces of the cope of casting casting shrinkage Voids formed in cast products when insufficient molten metal is fed into the solidifying casting to make up for the volume loss due to cooling. See also liquid shrinkage, shrinkage cavity, solidification shrinkage, and solid shrinkage catastrophic wear Rapidly occurring or accelerating surface damage, deterioration, or change of shape caused by wear to such a degree that the service life of a part is appreciably shortened or its function is destroyed cathode The electrode of an electrolytic cell at which reduction is the principal reaction(Electrons flow toward the cathode in the external circuit )Contrast with anode caustic cracking A form of stress-corrosion cracking most frequently encountered in carbon steels or iron-chromium nickel alloys that are exposed to concentrated hydroxide solutions at temperatures of 200 to 250C (400 to 480F). See also caustic embrittlement caustic embrittlement A form of hydrogen embrittlement sometimes caused by caustic cleaning of steel parts, especially those that have been hardened to relatively high strength levels. See also hydrogen embrittlement cavitation (1)The formation and rapid collapse, within a liquid, of cavities or bubbles that contain vapor or gas or both. Cavitation caused by severe turbulent flow often leads to cavitation damage of adjacent materials which may include loss of material or changes in surface properties. (2) The description of microscale oid formation, primarily in the grain boundaries during high-temperature deformation cavitation erosion See cavitation
(1) An indented valley in the surface of a sand casting due to expansion of the molding sand. (2) A local waviness in metal bar or sheet, usually transverse to the direction of rolling, caused by inconsistencies in the temperature or thickness of the material being rolled. buckling A compression and torsion phenomenon that occurs when, after some critical level of load, a bulge, bend, bow, kink, or other wavy condition is produced in a beam, column, plate, bar, or sheet product. The level of stress that causes buckling in a given component is dependent mainly on geometry and elastic modulus, but in some shapes, yield strength also has a strong influence on the resistence to buckling. bulk modulus See bulk modulus of elasticity. bulk modulus of elasticity, K The measure of resistance to change in volume; the ratio of hydrostatic stress (σm) to the corresponding unit change in volume (ΔV). This elastic constant can be expressed by: 1 / / m p K V V V V s b - === D D where K is the bulk modulus of elasticity, σm is hydrostatic or mean normal stress, p is hydrostatic pressure, and β is compressibility. Also known as bulk modulus, hydrostatic modulus, and volumetric modulus of elasticity. burning (1) Permanently damaging a metal or alloy by heating to cause either incipient melting or intergranular oxidation. See also overheating and grain-boundary liquation. (2) In grinding, getting the work hot enough to cause discoloration or to change the microstructure by tempering or hardening. C carbon flotation Free graphite that has separated from the molten iron in a cast iron. This imperfection tends to occur at the upper surfaces of the cope of castings. casting shrinkage Voids formed in cast products when insufficient molten metal is fed into the solidifying casting to make up for the volume loss due to cooling. See also liquid shrinkage, shrinkage cavity, solidification shrinkage, and solid shrinkage. catastrophic wear Rapidly occurring or accelerating surface damage, deterioration, or change of shape caused by wear to such a degree that the service life of a part is appreciably shortened or its function is destroyed. cathode The electrode of an electrolytic cell at which reduction is the principal reaction. (Electrons flow toward the cathode in the external circuit.) Contrast with anode. caustic cracking A form of stress-corrosion cracking most frequently encountered in carbon steels or iron-chromiumnickel alloys that are exposed to concentrated hydroxide solutions at temperatures of 200 to 250 °C (400 to 480 °F). See also caustic embrittlement. caustic embrittlement A form of hydrogen embrittlement sometimes caused by caustic cleaning of steel parts, especially those that have been hardened to relatively high strength levels. See also hydrogen embrittlement. cavitation (1) The formation and rapid collapse, within a liquid, of cavities or bubbles that contain vapor or gas or both. Cavitation caused by severe turbulent flow often leads to cavitation damage of adjacent materials, which may include loss of material or changes in surface properties. (2) The description of microscale void formation, primarily in the grain boundaries during high-temperature deformation. cavitation erosion See cavitation