test 2 vocab Flashcards
modulus of elasticity (E):
The ratio of stress to strain when deformation is totally elastic; also a measure of the stiffness of a material.
elastic deformation:
Deformation that is nonpermanent—that is, totally recovered upon release of an applied stress.
plastic deformation:
Deformation that is permanent or nonrecoverable after release of the applied load. It is accompanied by permanent atomic displacements.
yielding:
The onset of plastic deformation. (begins to deform indefinetly)
proportional limit:
The point on a stress-strain curve at which the straight-line proportionality between stress and strain ceases. (point where the line starts to curve over)
yield strength (σy):
The stress required to produce a very slight yet specified amount of plastic strain; a strain offset of 0.002 is commonly used.
tensile strength (TS):
The maximum engineering stress, in tension, that may be sustained without fracture. Often termed ultimate (tensile) strength.
ductility:
A measure of a material’s ability to undergo appreciable plastic deformation before fracture; it may be expressed as percent elongation (%EL) or percent reduction in area (%RA) from a tensile tes
resilience:
The capacity of a material to absorb energy when it is elastically deformed.
toughness:
A mechanical characteristic that may be expressed in three contexts: (1) the measure of a material’s resistance to fracture when a crack (or other stress-concentrating defect) is present; (2) the ability of a material to absorb energy and plastically deform before fracturing; and (3) the total area under the material’s tensile engineering stress-strain curve taken to fracture.
engineering stress:
The instantaneous load applied to a specimen divided by its cross-sectional area before any deformation.
engineering strain:
The change in gauge length of a specimen (in the direction of an applied stress) divided by its original gauge length. (pushing out or change of length or width)
shear:
A force applied so as to cause or tend to cause two adjacent parts of the same body to slide relative to each other in a direction parallel to their plane of contact.(pushes sideways at the top)
anelastic deformation:
Time-dependent elastic (nonpermanent) deformation.
Poisson’s ratio (ν):
For elastic deformation, the negative ratio of lateral and axial strains that result from an applied axial stress.
true stress (σT):
The instantaneous applied load divided by the instantaneous cross-sectional area of a specimen.
true strain (εT):
The natural logarithm of the ratio of instantaneous gauge length to original gauge length of a specimen being deformed by a uniaxial force.
hardness:
The measure of a material’s resistance to deformation by surface indentation or by abrasion.
design stress (σd):
Product of the calculated stress level (on the basis of estimated maximum load) and a design factor (which has a value greater than unity). Used to protect against unanticipated failure.
safe stress (σw):
A stress used for design purposes; for ductile metals, it is the yield strength divided by a factor of safety.
slip:
Plastic deformation as the result of dislocation motion; also, the shear displacement of two adjacent planes of atoms.
dislocation density:
The total dislocation length per unit volume of material; alternatively, the number of dislocations that intersect a unit area of a random surface section.
lattice strain:
Slight displacements of atoms relative to their normal lattice positions, normally imposed by crystalline defects such as dislocations, and interstitial and impurity atoms.
slip system:
The combination of a crystallographic plane and, within that plane, a crystallographic direction along which slip (i.e., dislocation motion) occurs.
({} and [])
resolved shear stress:
An applied tensile or compressive stress resolved into a shear component along a specific plane and direction within that plane.
critical resolved shear stress (τcrss):
The shear stress, resolved within a slip plane and direction, required to initiate slip.
solid-solution strengthening:
Hardening and strengthening of metals that result from alloying in which a solid solution is formed. The presence of impurity atoms restricts dislocation mobility.
strain hardening:
The increase in hardness and strength of a ductile metal as it is plastically deformed below its recrystallization temperature.
cold working:
The plastic deformation of a metal at a temperature below that at which it recrystallizes.
recovery:
The relief of some of the internal strain energy of a previously cold-worked metal, usually by heat treatment.
recrystallization:
The formation of a new set of strain-free grains within a previously cold-worked material; normally, an annealing heat treatment is necessary.
recrystallization temperature:
For a particular alloy, the minimum temperature at which complete recrystallization occurs within approximately 1 h.
grain growth:
The increase in average grain size of a polycrystalline material; for most materials, an elevated-temperature heat treatment is necessary.
ductile fracture:
A mode of fracture attended by extensive gross plastic deformation.
brittle fracture:
Fracture that occurs by rapid crack propagation and without appreciable macroscopic deformation.
transgranular fracture:
Fracture of polycrystalline materials by crack propagation through the grains.
intergranular fracture:
Fracture of polycrystalline materials by crack propagation along grain boundaries.
fracture mechanics:
A technique of fracture analysis used to determine the stress level at which preexisting cracks of known size will propagate, leading to fracture.
stress raiser:
A small flaw (internal or surface) or a structural discontinuity at which an applied tensile stress will be amplified and from which cracks may propagate.
fracture toughness (Kc):
The measure of a material’s resistance to fracture when a crack is present.
plane strain:
The condition, important in fracture mechanical analyses, in which, for tensile loading, there is zero strain in a direction perpendicular to both the stress axis and the direction of crack propagation; this condition is found in thick plates, and the zero-strain direction is perpendicular to the plate surface.
plane strain fracture toughness (KIc):
For the condition of plane strain, the measure of a material’s resistance to fracture when a crack is present.
Charpy test:
One of two tests that may be used to measure the impact energy or notch toughness of a standard notched specimen. An impact blow is imparted to the specimen by means of a weighted pendulum.
Izod test:
One of two tests that may be used to measure the impact energy of a standard notched specimen. An impact blow is imparted to the specimen by a weighted pendulum.
impact energy (notch toughness):
A measure of the energy absorbed during the fracture of a specimen of standard dimensions and geometry when subjected to very rapid (impact) loading. Charpy and Izod impact tests are used to measure this parameter, which is important in assessing the ductile-to-brittle transition behavior of a material.
ductile-to-brittle transition:
The transition from ductile to brittle behavior with a decrease in temperature exhibited by some low-strength steel (BCC) alloys; the temperature range over which the transition occurs is determined by Charpy and Izod impact tests.
fatigue:
Failure, at relatively low stress levels, of structures that are subjected to fluctuating and cyclic stresses.
fatigue limit:
For fatigue, the maximum stress amplitude level below which a material can endure an essentially infinite number of stress cycles and not fail.
fatigue strength:
The maximum stress level that a material can sustain without failing, for some specified number of cycles.
fatigue life (Nf):
The total number of stress cycles that cause a fatigue failure at some specified stress amplitude.
case hardening:
Hardening of the outer surface (or case) of a steel component by a carburizing or nitriding process; used to improve wear and fatigue resistance.
thermal fatigue:
A type of fatigue failure in which the cyclic stresses are introduced by fluctuating thermal stresses.
corrosion fatigue:
A type of failure that results from the simultaneous action of a cyclic stress and chemical attack.
creep:
creep: The time-dependent permanent deformation that occurs under stress; for most materials it is important only at elevated temperatures.
component:
A chemical constituent (element or compound) of an alloy that may be used to specify its composition.
system:
Two meanings are possible: (1) a specific body of material being considered, and (2) a series of possible alloys consisting of the same components.
solubility limit:
The maximum concentration of solute that may be added without forming a new phase.
phase:
A homogeneous portion of a system that has uniform physical and chemical characteristics.
equilibrium (phase):
The state of a system in which the phase characteristics remain constant over indefinite time periods. At equilibrium the free energy is a minimum.
free energy:
A thermodynamic quantity that is a function of both the internal energy and entropy (or randomness) of a system. At equilibrium, the free energy is at a minimum.
