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MATSE 201 Mechanics Quiz Review
Mechanical Properties of Solids
55
Science
Undergraduate 3
11/17/2010

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Cards

Term
engineering stress
Definition

σ = load/Ao     [N/m2]

 

Ao = initial x-sectional area

Term
engineering strain
Definition

ε = (l - lo)/lo

 

lo = initial length

l = length under stress

Term
basic stress-strain graph for a ductile metal
Definition
[image]
Term
For tensile stress, σ and ε are ______.
Definition
positive
Term
For compressive stress, σ and ε are ______.
Definition
negative
Term
angular stress and strain
Definition
[image]
Term
deformation regions graph
Definition
[image]
Term
elastic deformation
Definition
non-permanent
follows Hooke's Law
Term
Hooke's Law for elastic deformation
Definition

σ = Eε

 

 

E = Young's modulus

AKA "elastic modulus"

AKA "modulus of elasticity"

 

Term
How do bond strength and stiffness vary with Young's modulus?
Definition
as E ↑, stiffness ↑, bond strength ↑
Term
elastic energy density
Definition
given as the area under the stress strain curve
Term
sample stress-strain curves for material types
Definition
[image]
Term
elastic energy density equation
Definition
elastic energy = ½σE = ½Eε2
Term
longitudinal and transverse strain
and Poisson's ratio
Definition
[image]
Term
shear stress and strain equations
Definition

τ = Gγ

E = 2G(1 + ν)

 

where G = shear modulus

AKA modulus of rigidity


Term
deformation graph
yield point (onset of plastic deformation)
Tensile strength (maximum of stress-strain curve)
Definition
[image]
Term
Why is the regular stress-strain curve of a material misleading?
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.
Term
What is the role of dislocations in ductility?
Definition
Dislocations can increase ductility by facilitating slip.
Term
Where does slip most readily occur and why?
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.
Term
What is the relative susceptibility to slip of FCC, BCC, and HCP crystal structures?
Definition
FCC - most ductile (12 slip systems)
BCC - appreciably ductile (12 slip systems)
HCP - least ductile (3 slip systems)
Term
What is a slip system?
Definition
# slip systems = (# slip planes)*(# slip directions)
Term
Why does slip not generally occur in ceramics?
Definition
-Burger's vector (slip distance) is larger because it involves more than one atom
-sliding planes means bringing like charges near each other
Term
define the phenomenon of viscoelasticity
Definition
glasses and polymers may behave elastically at low T and flow at high T
Term
Elastomers can exhibit increasing engineering strain with stress. Why?
Definition
[image]
Term
bend test setup diagram
Definition
[image]
Term
stress-strain curve from bend test
Definition
[image]
Term
Griffith crack model
Definition
[image]
Term
Why is σmax greater for compressive stress than for tensile stress?
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.

 

Term
how does hardness relate to tensile strength and yield strength?
Definition
as hardness ↑, T.S. ↑, σy ↑, ductility ↓
Term
interpreting hardness and ductility from stress-strain graph
Definition
[image]
Term
list the methods of hardening
Definition
solution hardening
strain hardening
cold-working
precipitation hardening
grain size size reduction
Term
solution hardening
Definition
put a solute atom in the metal
this impedes dislocation movement
Term
strain hardening
Definition
create dislocations by bending material
there get to be too many, and they impede each other's movement
Term
cold working
Definition
squish a material, when cold, through rollers
this creates more dislocations
Term
precipitation hardening
Definition
[image]
Term
grain size reduction
Definition
smaller grain size means more grain boundaries, which impede dislocation movement
Term
recovering ductility
Definition

annealing (heat & grains recrystallize) reverses strain-hardening

upon annealing, tensile strength ↓, ductility ↑

Term
creep
Definition
permanent deformation occurring at high temperature for a material under constant load over a long time
Term
Why are creep mechanisms diffusion dependent?
Definition
[image]
Term
creep testing
Definition
apply constant load to material and measure long-term deformation
Term
stages of creep
Definition
[image]
Term
steady state creep rate
Definition

 ......................

εs = Kσne(Q / RT)

Term
fracture morphology of
ductile metal
Definition
"cup & cone"
Term
fracture morphology of
brittle metal
Definition
regular break
Term
fracture morphology of
ceramic
Definition
"mirror-mist-hackle"
Term
strength
Definition
measure of a material's ability to withstand stress or strain
Term
hardness
Definition
measure of a material's ability to withstand indentation, distortion, and scratching
Term
ductility
Definition
measure of a material's ability to deform under tensile stress
Term
toughness
Definition
measure of material's resistance to fracture when stressed
Term
On a stress-strain curve, the first part is _____ deformation, which is ______ when the load is removed.
Definition
elastic
recovered
Term
On a stress-strain curve, the second part is _____ deformation, which is ______ when the load is removed.
Definition
plastic
permanent
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 _____.
Definition
Poisson ratio
Term
Why are ceramic materials harder yet more brittle than metals?
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
Term
Why is Ni more ductile than Co when they both have similar bond strength and melting points?
Definition
Ni is more ductile because its FCC crystal structure is more ductile than Co's HCP crystal structure
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.
Definition
obeyed = solution hardening
not obeyed = precipitation hardening
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