Term
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Definition
σ = load/Ao [N/m2]
Ao = initial x-sectional area |
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Term
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Definition
ε = (l - lo)/lo
lo = initial length
l = length under stress |
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Term
| basic stress-strain graph for a ductile metal |
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Definition
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Term
| For tensile stress, σ and ε are ______. |
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Definition
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Term
| For compressive stress, σ and ε are ______. |
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Definition
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Term
| angular stress and strain |
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Definition
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Term
| deformation regions graph |
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Definition
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Term
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Definition
non-permanent
follows Hooke's Law |
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Term
| Hooke's Law for elastic deformation |
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Definition
σ = Eε
E = Young's modulus
AKA "elastic modulus"
AKA "modulus of elasticity"
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Term
| How do bond strength and stiffness vary with Young's modulus? |
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Definition
| as E ↑, stiffness ↑, bond strength ↑ |
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Term
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Definition
| given as the area under the stress strain curve |
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Term
| sample stress-strain curves for material types |
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Definition
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Term
| elastic energy density equation |
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Definition
| elastic energy = ½σE = ½Eε2 |
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Term
longitudinal and transverse strain
and Poisson's ratio |
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Definition
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Term
| shear stress and strain equations |
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Definition
τ = Gγ
E = 2G(1 + ν)
where G = shear modulus
AKA modulus of rigidity
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Term
deformation graph
yield point (onset of plastic deformation)
Tensile strength (maximum of stress-strain curve) |
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Definition
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Term
| Why is the regular stress-strain curve of a material misleading? |
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Definition
Because of necking (area decrease), engineering stress is artificially low. The "true stress" will show a higher engineering stress.
Necking starts after the yield point. |
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Term
| What is the role of dislocations in ductility? |
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Definition
| Dislocations can increase ductility by facilitating slip. |
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Term
| Where does slip most readily occur and why? |
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Definition
| Slip occurs most readily in high density planes along a high density direction, because denser planes have atoms closer together and denser directions make for shorter slip distances. |
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Term
| What is the relative susceptibility to slip of FCC, BCC, and HCP crystal structures? |
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Definition
FCC - most ductile (12 slip systems)
BCC - appreciably ductile (12 slip systems)
HCP - least ductile (3 slip systems) |
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Term
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Definition
| # slip systems = (# slip planes)*(# slip directions) |
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Term
| Why does slip not generally occur in ceramics? |
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Definition
-Burger's vector (slip distance) is larger because it involves more than one atom
-sliding planes means bringing like charges near each other |
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Term
| define the phenomenon of viscoelasticity |
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Definition
| glasses and polymers may behave elastically at low T and flow at high T |
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Term
| Elastomers can exhibit increasing engineering strain with stress. Why? |
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Definition
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Term
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Definition
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Term
| stress-strain curve from bend test |
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Definition
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Term
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Definition
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Term
| Why is σmax greater for compressive stress than for tensile stress? |
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Definition
σmax ↑ as r ↓
Because the compressive stress squishes the crack and makers r effectively smaller, σmax can be higher.
It's the opposite for tensile stress.
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Term
| how does hardness relate to tensile strength and yield strength? |
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Definition
| as hardness ↑, T.S. ↑, σy ↑, ductility ↓ |
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Term
| interpreting hardness and ductility from stress-strain graph |
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Definition
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Term
| list the methods of hardening |
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Definition
solution hardening
strain hardening
cold-working
precipitation hardening
grain size size reduction |
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Term
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Definition
put a solute atom in the metal
this impedes dislocation movement |
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Term
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Definition
create dislocations by bending material
there get to be too many, and they impede each other's movement |
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Term
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Definition
squish a material, when cold, through rollers
this creates more dislocations |
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Term
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Definition
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Term
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Definition
| smaller grain size means more grain boundaries, which impede dislocation movement |
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Term
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Definition
annealing (heat & grains recrystallize) reverses strain-hardening
upon annealing, tensile strength ↓, ductility ↑ |
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Term
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Definition
| permanent deformation occurring at high temperature for a material under constant load over a long time |
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Term
| Why are creep mechanisms diffusion dependent? |
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Definition
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Term
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Definition
| apply constant load to material and measure long-term deformation |
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Term
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Definition
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Term
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Definition
......................
εs = Kσne(Q / RT) |
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Term
fracture morphology of
ductile metal |
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Definition
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Term
fracture morphology of
brittle metal |
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Definition
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Term
fracture morphology of
ceramic |
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Definition
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Term
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Definition
| measure of a material's ability to withstand stress or strain |
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Term
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Definition
| measure of a material's ability to withstand indentation, distortion, and scratching |
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Term
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Definition
| measure of a material's ability to deform under tensile stress |
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Term
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Definition
| measure of material's resistance to fracture when stressed |
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Term
| On a stress-strain curve, the first part is _____ deformation, which is ______ when the load is removed. |
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Definition
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Term
| On a stress-strain curve, the second part is _____ deformation, which is ______ when the load is removed. |
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Definition
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Term
| During elastic deformation, a tensile or compressive strain parallel to the direction of an applied load will induce a strain perpendicular to the load having opposite sign and a magnitude determined by the _____. |
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Definition
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Term
| Why are ceramic materials harder yet more brittle than metals? |
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Definition
Ceramics are hard yet brittle because they have strong bonds between atoms with strong ionic/covalent character.
Burger's vector is larger because dislocation involves more than one atom
sliding planes means bringing like charges close |
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Term
| Why is Ni more ductile than Co when they both have similar bond strength and melting points? |
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Definition
| Ni is more ductile because its FCC crystal structure is more ductile than Co's HCP crystal structure |
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Term
Metals can be hardened by alloying with other metals.
An example of _____ hardening occurs in a system where the Hume-Rothery rules are obeyed.
An example of _____ hardening occurs in a system where they aren't. |
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Definition
obeyed = solution hardening
not obeyed = precipitation hardening |
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