ductile-brittle transition temperature dbtt) Temperature at which a marked change occurs in the fracture resistance of body-centered cubic and hexagonal close-packed metals from ductile behavior to brittle behavior. The transition occurs in those metals in which the yield strength increases sharply with decreasing temperature and which are capable of fracturing by cleavage or an intergranular mode with very little accompanying plastic deformation The transition temperature also depends on strain rate ductile crack propagation Slow crack propagation that is accompanied by noticeable plastic deformation and requires energy to be ductile erosion behavior Erosion behavior having characteristic properties(such as considerable plastic deformation) that can be duchie exposed surface at low values of angle of attack. Contrast with brittle erosion behavior ern forms on the associated with ductile fracture of the exposed solid surface. a characteristic ripple ractu Macroscale and microscale term. Used at the macroscale to indicate visible plastic deformation associated with fracture (often implies high energy absorption). Used at the microscale to describe plastic deformation associated with fracture, typically by microvoid coalescence. Contrast with brittle ductility The ability of a material to deform plastically before fracturing. Measured by elongation or reduction of area in a tension test, by height of the cup formed, in a cupping test, or by the radius or angle of bend in a bend test. Contrast with brittleness; see also plastic deformation Moving, or having high velocity. Frequently used with high strain-rate 0.1 s) testing of metal effective crack size, ae The physical crack size augmented for the effects of crack-tip plastic deformation. Sometimes the effective crack size is calculated from a measured value of a physical crack size plus a calculated valu of a plastic-zone adjustment. A preferred method for calculation of effective crack size compares compliance from the secant of a load-deflection trace with the elastic compliance from a calibration for the type of specimen effective stress A calculated parameter used in a mathematical expression that predicts the onset of an event( typically yield and fatigue failure) when a critical value of the effective stress is obtained. The most common effective stress is the von mises stress elastic constants The factors of proportionality that relate elastic displacement of a material to applied forces. See also bulk modulus of elasticity, modulus of elasticity, Poisson s ratio, and shear modulus elastic deformation Shape change and volume change due to an applied stress that is low enough so that the material returns to its original shape and volume when the stress is removed elasticity The property of a material by virtue of which deformation caused by stress disappears on removal of the stress. a perfectly elastic body completely recovers its original shape and dimensions after release of stress elastic limit The maximum stress a material is capable of sustaining without any permanent shape change remaining on complete release of the stress. See also proportional limit elastic strain The mathematical value that quantifies elastic deformation elongation
ductile-brittle transition temperature (DBTT) Temperature at which a marked change occurs in the fracture resistance of body-centered cubic and hexagonal close-packed metals from ductile behavior to brittle behavior. The transition occurs in those metals in which the yield strength increases sharply with decreasing temperature and which are capable of fracturing by cleavage or an intergranular mode with very little accompanying plastic deformation. The transition temperature also depends on strain rate. ductile crack propagation Slow crack propagation that is accompanied by noticeable plastic deformation and requires energy to be supplied from outside the body. Contrast with brittle crack propagation. ductile erosion behavior Erosion behavior having characteristic properties (such as considerable plastic deformation) that can be associated with ductile fracture of the exposed solid surface. A characteristic ripple pattern forms on the exposed surface at low values of angle of attack. Contrast with brittle erosion behavior. ductile fracture Macroscale and microscale term. Used at the macroscale to indicate visible plastic deformation associated with fracture (often implies high energy absorption). Used at the microscale to describe plastic deformation associated with fracture, typically by microvoid coalescence. Contrast with brittle fracture. ductility The ability of a material to deform plastically before fracturing. Measured by elongation or reduction of area in a tension test, by height of the cup formed, in a cupping test, or by the radius or angle of bend in a bend test. Contrast with brittleness; see also plastic deformation. dynamic Moving, or having high velocity. Frequently used with high strain-rate (≥0.1 s-1) testing of metal specimens. E effective crack size, ae The physical crack size augmented for the effects of crack-tip plastic deformation. Sometimes the effective crack size is calculated from a measured value of a physical crack size plus a calculated value of a plastic-zone adjustment. A preferred method for calculation of effective crack size compares compliance from the secant of a load-deflection trace with the elastic compliance from a calibration for the type of specimen. effective stress A calculated parameter used in a mathematical expression that predicts the onset of an event (typically yield and fatigue failure) when a critical value of the effective stress is obtained. The most common effective stress is the von Mises stress. elastic constants The factors of proportionality that relate elastic displacement of a material to applied forces. See also bulk modulus of elasticity, modulus of elasticity, Poisson's ratio, and shear modulus. elastic deformation Shape change and volume change due to an applied stress that is low enough so that the material returns to its original shape and volume when the stress is removed. elasticity The property of a material by virtue of which deformation caused by stress disappears on removal of the stress. A perfectly elastic body completely recovers its original shape and dimensions after release of stress. elastic limit The maximum stress a material is capable of sustaining without any permanent shape change remaining on complete release of the stress. See also proportional limit. elastic strain The mathematical value that quantifies elastic deformation. elongation
a term used in mechanical testing to describe the amount of extension of a test piece when stressed Expressed in units of length or as strain(percent change in length). Quantitative value describing the length increase of the gage length of a tensile-test bar due to the deformation up to and including the fracture process. Note that elongation(expressed as length or strain) is not an inherent material property but depends on the dimension of the specimen tested as well as whether it is measured under load, such as with a laser extensometer, or after fracture, generally after manually remating the fracture surfaces in a fixture embrittlement The severe loss of ductility and/or toughness of a material end grain rain flow lines that intersect with the exposed surface of the ends of bar stock, tubing, or the parting lines of forgings. A long, narrow test specimen sectioned so that the grain is parallel to the longitudinal axis of the specimen has no exposed end grain, except at the extreme ends. In contrast, a corresponding nd- gr s especially pronounced in the short-transverse direction on die forgings designed with a d/e grain specimen cut in the transverse direction has end-grain exposure at all points along its length. End Preferential corrosive attack of grains exposed by cutting through the cross section or at the parting lines of forgings endurance limit Obsolete term used to describe a characteristic in components subject to fatigue cracking. The use of this term is now discouraged because it does not reflect the current understanding of how fatigue cracks initiate and grow. It referred to the maximum stress below which a material can presumably endure an infinite number of stress cycles. If the stress is not completely reversed, the value of the mean stress, the minimum stress, or the stress ratio also should be stated. Compare with fatigue limit erosion Destruction of materials by the abrasive action of moving fluids, usually accelerated by the presence of solid particles carried with the fluid. See also erosion-corrosion erosion-corrosion A conjoint action involving corrosion and erosion in the presence of a moving corrosive fluid, leading to the accelerated loss of material (1) Localized corrosion attack at the microscopic scale. Typically seen on a polished and etched metallographic specimen. Etch pits typically have recognizable, simple geometric shape(square, rectangle, triangle) and therefore reveal, in a qualitative way, the orientation of a grain. (2)A conjoint action involving corrosion and erosion in the presence of a moving corrosive fluid, leading to the accelerated loss of material exfoliation Corrosion that proceeds from the sites of initiation along planes parallel to the surface, generally along grain boundaries, forming bulky corrosion products that create generally undesired free internal surfaces and give rise to a layered appearance failure (1)A general term used to imply that a part in service(a)has become completely inoperable,(b)is still operable but is incapable of satisfactorily performing its intended function, or(c) has seriously, to the point that it has become unreliable or unsafe for continued use. (2)Also commonly applied to manufacturing processes that produce components that do not meet specifications false brinelling Damage to a solid bearing surface characterized by indentations not caused by plastic deformation resulting from overload but thought to be due to other causes such as fretting corrosion. See also Brinelling fatigue Thefileisdownloadedfromwww.bzfxw.com
A term used in mechanical testing to describe the amount of extension of a test piece when stressed. Expressed in units of length or as strain (percent change in length). Quantitative value describing the length increase of the gage length of a tensile-test bar due to the deformation up to and including the fracture process. Note that elongation (expressed as length or strain) is not an inherent material property but depends on the dimension of the specimen tested as well as whether it is measured under load, such as with a laser extensometer, or after fracture, generally after manually remating the fracture surfaces in a fixture. embrittlement The severe loss of ductility and/or toughness of a material. end grain Grain flow lines that intersect with the exposed surface of the ends of bar stock, tubing, or the parting lines of forgings. A long, narrow test specimen sectioned so that the grain is parallel to the longitudinal axis of the specimen has no exposed end grain, except at the extreme ends. In contrast, a corresponding specimen cut in the transverse direction has end-grain exposure at all points along its length. End grain is especially pronounced in the short-transverse direction on die forgings designed with a flash line. end-grain attack Preferential corrosive attack of grains exposed by cutting through the cross section or at the parting lines of forgings. endurance limit Obsolete term used to describe a characteristic in components subject to fatigue cracking. The use of this term is now discouraged, because it does not reflect the current understanding of how fatigue cracks initiate and grow. It referred to the maximum stress below which a material can presumably endure an infinite number of stress cycles. If the stress is not completely reversed, the value of the mean stress, the minimum stress, or the stress ratio also should be stated. Compare with fatigue limit. erosion Destruction of materials by the abrasive action of moving fluids, usually accelerated by the presence of solid particles carried with the fluid. See also erosion-corrosion. erosion-corrosion A conjoint action involving corrosion and erosion in the presence of a moving corrosive fluid, leading to the accelerated loss of material. etch pits (1) Localized corrosion attack at the microscopic scale. Typically seen on a polished and etched metallographic specimen. Etch pits typically have recognizable, simple geometric shape (square, rectangle, triangle) and therefore reveal, in a qualitative way, the orientation of a grain. (2) A conjoint action involving corrosion and erosion in the presence of a moving corrosive fluid, leading to the accelerated loss of material. exfoliation Corrosion that proceeds from the sites of initiation along planes parallel to the surface, generally along grain boundaries, forming bulky corrosion products that create generally undesired free internal surfaces and give rise to a layered appearance. F failure (1) A general term used to imply that a part in service (a) has become completely inoperable, (b) is still operable but is 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. (2) Also commonly applied to manufacturing processes that produce components that do not meet specifications. false Brinelling Damage to a solid bearing surface characterized by indentations not caused by plastic deformation resulting from overload but thought to be due to other causes such as fretting corrosion. See also Brinelling. fatigue The file is downloaded from www.bzfxw.com
The phenomenon leading to fracture or cracking under repeated or fluctuating stresses having a maximum value less than the ultimate tensile strength(and for ductile materials, usually less than the yield strength) of the material. See also fatigue failure, high-cycle fatigue, low-cycle fatigue, yield strength, and ultimate strength fatigue crack growth rate, da/dN The rate of crack extension caused by constant-amplitude fatigue loading, expressed in terms of crack extension per cycle of load application. Note that this is not a single-value parameter. See also Paris law fatigue failure Failure that occurs when a specimen undergoing cyclic loading, due to applied loads or temperature variations, completely fractures into two parts or has been significantly reduced in stiffness by cracking Fatigue failure generally occurs at loads that, when applied statically, would produce little perceptible effect fatigue life The number of stress cycles that can be sustained prior to failure under a stated test condition fatigue limit (1) The maximum stress that presumably leads to fatigue fracture in a specified number of stress cycles If the stress is not completely reversed, the value of the mean stress, the minimum stress, or the stress ratio also should be stated. Compare with endurance limit. Preference is to quote the medial value of the stress, based on statistical analysis of the experimental data. (2) The limiting value of median fatigue strength as the number of cycles becomes very large(SAE definition). Note: certain materials and environments preclude the attainment of fatigue limits. Values tabulated as fatigue limits in literature are frequently(but not always)values for 50% survival at N cycles with zero mean stress fatigue notch factor, kr The ratio of the fatigue strength of an unnotched specimen to the fatigue strength of a notched specimen of the same material and condition; both strengths are determined at the same number of stress cycles fatigue notch sensitivity, q An estimate of the true effect of a notch(as contrasted to a theoretical effect based on the elastic stress concentration factor )or hole of a given size and shape on the fatigue properties of a material; measured by q=(kr-1(k-1), where kr is the fatigue notch factor and k, is the stress concentration factor. A material is said to be fully notch sensitive if q approaches a value of 1.0; it is not notch sensitive if the approaches fatigue ratio The fatigue limit under completely reversed flexural stress divided by the tensile strength for the sam alloy and condition fatigue strength The maximum stress that can be sustained for a specified number of stress cycles without failure, the stress being completely reversed within each cycle, unless otherwise stated fatigue striation ( 1)A microscale fatigue fracture feature sometimes observed that indicates the position of the crack front after each succeeding cycle of stress. The distance between striations indicates the advance of the crack front during one stress cycle, and a line normal to the striation indicates the direction of local crack propagation. Not to be confused with beach marks, which are much larger(macroscopic)and form differently. Also not to be confused with other similarly appearing microscale features, such as a stretch zone at the tip of a preexisting cracklike imperfection, a Wallner line, and so on. (2) In glasses, a fracture-surface marking consisting of the separation of the advancing crack front into separate fracture planes. Also known as coarse hackle, step fracture, or lance. Striations may also be called sharks teeth or whiskers fatigue wear Wear of a solid surface caused by fracture arising from material fatigue fiber The characteristic of wrought metal that indicates directional properties. It can be revealed by etching of a longitudinal section or is manifested by the fibrous or woody appearance of a fracture. It is caused either by(a) extension of the constituents of the metal, both metallic and nonmetallic, in the direction of
The phenomenon leading to fracture or cracking under repeated or fluctuating stresses having a maximum value less than the ultimate tensile strength (and for ductile materials, usually less than the yield strength) of the material. See also fatigue failure, high-cycle fatigue, low-cycle fatigue, yield strength, and ultimate strength. fatigue crack growth rate, da/dN The rate of crack extension caused by constant-amplitude fatigue loading, expressed in terms of crack extension per cycle of load application. Note that this is not a single-value parameter. See also Paris law. fatigue failure Failure that occurs when a specimen undergoing cyclic loading, due to applied loads or temperature variations, completely fractures into two parts or has been significantly reduced in stiffness by cracking. Fatigue failure generally occurs at loads that, when applied statically, would produce little perceptible effect. fatigue life The number of stress cycles that can be sustained prior to failure under a stated test condition. fatigue limit (1) The maximum stress that presumably leads to fatigue fracture in a specified number of stress cycles. If the stress is not completely reversed, the value of the mean stress, the minimum stress, or the stress ratio also should be stated. Compare with endurance limit. Preference is to quote the medial value of the stress, based on statistical analysis of the experimental data. (2) The limiting value of median fatigue strength as the number of cycles becomes very large (SAE definition). Note: certain materials and environments preclude the attainment of fatigue limits. Values tabulated as fatigue limits in literature are frequently (but not always) values for 50% survival at N cycles with zero mean stress. fatigue notch factor, kf The ratio of the fatigue strength of an unnotched specimen to the fatigue strength of a notched specimen of the same material and condition; both strengths are determined at the same number of stress cycles. fatigue notch sensitivity, q An estimate of the true effect of a notch (as contrasted to a theoretical effect based on the elastic stress concentration factor) or hole of a given size and shape on the fatigue properties of a material; measured by q = (kf - 1)/(kt - 1), where kf is the fatigue notch factor and kt is the stress concentration factor. A material is said to be fully notch sensitive if q approaches a value of 1.0; it is not notch sensitive if the ratio approaches 0. fatigue ratio The fatigue limit under completely reversed flexural stress divided by the tensile strength for the same alloy and condition. fatigue strength The maximum stress that can be sustained for a specified number of stress cycles without failure, the stress being completely reversed within each cycle, unless otherwise stated. fatigue striation (1) A microscale fatigue fracture feature sometimes observed that indicates the position of the crack front after each succeeding cycle of stress. The distance between striations indicates the advance of the crack front during one stress cycle, and a line normal to the striation indicates the direction of local crack propagation. Not to be confused with beach marks, which are much larger (macroscopic) and form differently. Also not to be confused with other similarly appearing microscale features, such as a stretch zone at the tip of a preexisting cracklike imperfection, a Wallner line, and so on. (2) In glasses, a fracture-surface marking consisting of the separation of the advancing crack front into separate fracture planes. Also known as coarse hackle, step fracture, or lance. Striations may also be called shark's teeth or whiskers. fatigue wear Wear of a solid surface caused by fracture arising from material fatigue. fiber The characteristic of wrought metal that indicates directional properties. It can be revealed by etching of a longitudinal section or is manifested by the fibrous or woody appearance of a fracture. It is caused either by (a) extension of the constituents of the metal, both metallic and nonmetallic, in the direction of