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flipped question answer Flashcards

1
Q

shear

A

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

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2
Q

engineering stress σ

A

The instantaneous load applied to a specimen divided by its cross-sectional area before any deformation.

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3
Q

engineering strain (E)

A

The change in gauge length of a specimen (in the direction of an applied stress) divided by its original gauge length.

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4
Q

modulus of elasticity

A

The ratio of stress to strain when deformation is totally elastic; also a measure of the stiffness of a material.

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5
Q

elastic deformation:

A

Deformation that is nonpermanent—that is, totally recovered upon release of an applied stress.

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6
Q

elastic recovery

A

Nonpermanent deformation recovered or regained upon release of a mechanical stress

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7
Q

anelastic deformation

A

Time-dependent elastic (nonpermanent) deformation.

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8
Q

yielding

A

The onset of plastic deformation.

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9
Q

proportional limit

A

The point on a stress-strain curve at which the straight-line proportionality between stress and strain ceases.

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10
Q

yield strength

A

The stress required to produce a very slight yet specified amount of plastic strain; a strain offset of 0.002 is commonly used

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11
Q

tensile strength

A

The maximum engineering stress, in tension, that may be sustained without fracture. Often termed ultimate (tensile) strength.

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12
Q

ductility

A

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 test.

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13
Q

resilience

A

The capacity of a material to absorb energy when it is elastically deformed.

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14
Q

toughness

A

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.

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15
Q

true stress

A

The instantaneous applied load divided by the instantaneous cross-sectional area of a specimen

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16
Q

true strain

A

The natural logarithm of the ratio of instantaneous gauge length to original gauge length of a specimen being deformed by a uniaxial force.

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17
Q

flexural strength

A

Stress at fracture from a bend (or flexure) test.

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18
Q

elastomer

A

A polymeric material that may experience large and reversible elastic deformations.

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19
Q

viscoelasticity

A

A type of deformation exhibiting the mechanical characteristics of viscous flow and elastic deformation.

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20
Q

relaxation modulus

A

For viscoelastic polymers, the time-dependent modulus of elasticity. It is determined from stress relaxation measurements as the ratio of stress (taken at some time after the load application—normally 10 s) to strain

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21
Q

hardness

A

The measure of a material’s resistance to deformation by surface indentation or by abrasion.

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22
Q

design stress

A

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.

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23
Q

safe stress

A

A stress used for design purposes; for ductile metals, it is the yield strength divided by a factor of safety

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24
Q

slip

A

Plastic deformation as the result of dislocation motion; also, the shear displacement of two adjacent planes of atoms.

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25
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.
26
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.
27
slip system
The combination of a crystallographic plane and, within that plane, a crystallographic direction along which slip (i.e., dislocation motion) occurs
28
resolved shear stress
An applied tensile or compressive stress resolved into a shear component along a specific plane and direction within that plane.
29
critical resolved shear stress
The shear stress, resolved within a slip plane and direction, required to initiate slip.
30
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.
31
strain hardening
The increase in hardness and strength of a ductile metal as it is plastically deformed below its recrystallization temperature.
32
cold working
The plastic deformation of a metal at a temperature below that at which it recrystallizes.
33
recovery
The relief of some of the internal strain energy of a previously cold-worked metal, usually by heat treatment.
34
recrystallization
The formation of a new set of strain-free grains within a previously cold-worked material; normally, an annealing heat treatment is necessary.
35
recrystallization temperature
For a particular alloy, the minimum temperature at which complete recrystallization occurs within approximately 1 h.
36
grain growth
The increase in average grain size of a polycrystalline material; for most materials, an elevated-temperature heat treatment is necessary.
37
drawing (metals)
A forming technique used to fabricate metal wire and tubing. Deformation is accomplished by pulling the material through a die by means of a tensile force applied on the exit side.
38
vulcanization
A nonreversible chemical reaction involving sulfur or another suitable agent in which crosslinks are formed between molecular chains in rubber materials. The rubber's modulus of elasticity and strength are enhanced.
39
ductile fracture
A mode of fracture attended by extensive gross plastic deformation.
40
brittle fracture
Fracture that occurs by rapid crack propagation and without appreciable macroscopic deformation.
41
transgranular fracture
Fracture of polycrystalline materials by crack propagation through the grains.
42
intergranular fracture
Fracture of polycrystalline materials by crack propagation along grain boundaries.
43
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
44
fracture toughness
The measure of a material's resistance to fracture when a crack is present.
45
plane strain:
The condition, 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.
46
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. (not done in class)
47
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.
48
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.
49
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.
50
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.
51
case hardening
Hardening of the outer surface of a steel component by a carburizing or nitriding process; used to improve wear and fatigue resistance.
52
thermal fatigue
A type of fatigue failure in which the cyclic stresses are introduced by fluctuating thermal stresses
53
corrosion fatigue
A type of failure that results from the simultaneous action of a cyclic stress and chemical attack
54
creep
The time-dependent permanent deformation that occurs under stress; for most materials it is important only at elevated temperatures.
55
solubility limit
The maximum concentration of solute that may be added without forming a new phase.
56
phase
A homogeneous portion of a system that has uniform physical and chemical characteristics.
57
metastable
A nonequilibrium state that may persist for a very long time.
58
isomorphous
Having the same structure. In the phase diagram sense, ________ means having the same crystal structure or complete solid solubility for all compositions.
59
tie line
A horizontal line constructed across a two-phase region of a binary phase diagram; its intersections with the phase boundaries on either end represent the equilibrium compositions of the respective phases at the temperature in question.
60
lever rule
A mathematical expression by which the relative phase amounts in a two-phase alloy at equilibrium may be computed,
61
solvus line
The locus of points on a phase diagram representing the limit of solid solubility as a function of temperature.
62
liquidus line
On a binary phase diagram, the line or boundary separating liquid- and liquid + solid-phase regions. For an alloy, the liquidus temperature is the temperature at which a solid phase first forms under conditions of equilibrium cooling
63
solidus line
On a phase diagram, the locus of points at which solidification is complete upon equilibrium cooling, or at which melting begins upon equilibrium heating
64
eutectic reaction
A reaction in which, upon cooling, a liquid phase transforms isothermally and reversibly into two intimately 2 solid phases.
65
eutectic structure
A two-phase microstructure (2 solids) resulting from the solidification (cooling) of a liquid having the _______ composition; the phases exist as lamellae that alternate with one another.
66
microconstituent
An element of the microstructure that has an identifiable and characteristic structure. It may consist of more than one phase, such as with pearlite.
67
primary phase
A phase that exists in addition to the eutectic structure.
68
terminal solid solution
A solid solution that exists over a composition range extending to either composition extreme of a binary phase diagram.
69
intermediate solid solution
A solid solution or phase having a composition range that does not extend to either of the pure components of the system
70
intermetallic compound:
A compound of two metals that has a distinct chemical formula. On a phase diagram it appears as an intermediate phase that exists over a very narrow range of compositions
71
eutectoid reaction
A reaction in which, upon cooling, one solid phase transforms isothermally and reversibly into two new solid phases that are intimately mixed.
72
peritectic reaction
A reaction in which, upon cooling, a solid and a liquid phase transform isothermally and reversibly to a solid phase having a different composition.
73
congruent transformation
A transformation of one phase to another of the same composition.
74
Gibbs phase rule
For a system at equilibrium, an equation that expresses the relationship between the number of phases present and the number of externally controllable variables
75
ferrite (iron)
Ceramic oxide materials composed of both divalent and trivalent cations (e.g., Fe2+ and Fe3+), some of which are ferrimagnetic.
76
austenite
Face-centered cubic iron; also iron and steel alloys that have the FCC crystal structure.
77
cementite
Iron carbide
78
pearlite
A two-phase microstructure found in some steels and cast irons; it results from the transformation of austenite of eutectoid composition and consists of alternating layers (or lamellae) of α-ferrite and cementite.
79
hypoeutectoid alloy
For an alloy system displaying a eutectoid, an alloy for which the concentration of solute is less than the eutectoid composition.
80
proeutectoid ferrite
Primary ferrite that exists in addition to pearlite for hypoeutectoid steels.
81
hypereutectoid alloy
For an alloy system displaying a eutectoid, an alloy for which the concentration of solute is greater than the eutectoid composition.
82
proeutectoid cementite
Primary cementite that exists in addition to pearlite for hypereutectoid steels.
83
nucleation
The initial stage in a phase transformation. It is evidenced by the formation of small particles of the new phase that are capable of growing.
84
supercooling
Cooling to below a phase transition temperature without the occurrence of the transformation.
85
superheating
Heating to above a phase transition temperature without the occurrence of the transformation.
86
coarse pearlite
Pearlite for which the alternating ferrite and cementite layers are relatively thick.
87
fine pearlite
Pearlite in which the alternating ferrite and cementite layers are relatively thin.
88
bainite
An austenitic transformation product found in some steels and cast irons. It forms at temperatures between those at which pearlite and martensite transformations occur. The microstructure consists of α-ferrite and a fine dispersion of cementite.
89
spheroidite
Microstructure found in steel alloys consisting of spherelike cementite particles within an α-ferrite matrix. It is produced by an appropriate elevated-temperature heat treatment of pearlite, bainite, or martensite and is relatively soft.
90
tempered martensite
The microstructural product resulting from a tempering heat treatment of a martensitic steel. The microstructure consists of extremely small and uniformly dispersed cementite particles embedded within a continuous α-ferrite matrix. Toughness and ductility are enhanced significantly by tempering.
91
martensite
A metastable iron phase supersaturated in carbon that is the product of a diffusionless (athermal) transformation from austenite.
92
athermal transformation
A reaction that is not thermally activated, and usually diffusionless, as with the martensitic transformation. Normally, the transformation takes place with great speed (i.e., is independent of time), and the extent of reaction depends on temperature.
93
solution heat treatment
the process used to form a solid solution by dissolving precipitate particles. Often, the solid solution is supersaturated and metastable at ambient conditions as a result of rapid cooling from an elevated temperature.
94
precipitation heat treatment
A heat treatment used to precipitate a new phase from a supersaturated solid solution. For precipitation hardening, it is termed artificial aging.
95
overaging
During precipitation hardening, aging beyond the point at which strength and hardness are at their maxima.
96
natural aging
For precipitation hardening, aging at room temperature.
97
artificial aging
For precipitation hardening, aging above room temperature.

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