Test 2 Flashcards
What allows a metal to plastically deform?
the movement of dislocations
What are the two types of dislocations?
edge and screw
What does a burger’s vector tell you about slip?
The slip direction (should know for FCC)
What does a slip system consist of?
a plane and a direction
What is the FCC slip system?
(111)+[110]
What is the equation for resolved shear stress and what do the terms mean?
resolved shear stress = applied stresscos(phi)cos(lamda)
Phi is the angle between the tensile axis and the normal to the slip plane.
Lamda is the angle between the tensile axis and the slip direction.
What equation do you use to find angles for phi and lamda in the resolved shear stress equation?
for vectors: a=[a1,a2,a3] and b=[b1,b2,b3]
theta=inversecos[{a1b1+a2b2+a3*b3)/(sqrt[(a1^2+a2^2+a3^2)(b1^2+b2^2+b3^2)])]
What is twinning?
A means of plastic deformation in which a shear force produces atomic displacement such that atoms on one side of the plane (the twin boundary) are located in mirror-image positions to atoms on the other side of the plane.
What are the mechanisms for strengthening metals?
- Cold Working/Strain Hardening
- Grain Size Reduction
- Precipitation Hardening
- Solid Solution Strengthening
How does Grain Size Reduction strengthen a metal?
When a dislocation passes into a different grain it must change directions. The smaller the grains, the more often it has to change directions, making it more difficult for it to move.
How does Solid Solution Strengthening work?
A host material is alloyed with impurity atoms that go into either substitutional or interstitial positions. This causes lattice strain and consequently dislocation movement restriction.
How does Strain Hardening/Cold Working work?
As dislocation density increases dislocation movement becomes more restricted.
How does Precipitation Hardening work?
Heat treatments are used to cause a formation of extremely small uniformly dispersed particles of a second phase within the original phase matrix. The precipitate acts as pinning points. Inverse relationship between yield strength and spacing between precipitates.
What is the Hall-Petch equation?
yield strength=sigma0+k/sqrt(d)
sigma0 and k are material constants
d is the average grain diameter
What is annealing?
Heat treatment that causes a material to revert to precold-worked states
What are the phases of annealing? Explain them.
Recovery - reduce dislocation density
Recrystallization - formation of a new set of grains with very few dislocations
Grain Growth - strain-free gains continue to grow. Grain growth causes a decrease in total boundary area which reduces total energy
What are the two types of fracture? Explain them
Ductile - deformation occurs before fracture (necking)
Brittle - little to no deformation occurs before fracture (clean break)
What is sigmam in terms of fracture mechanics?
maximum stress at tip of elliptical shaped crack. sigmam=2*sigma0*sqrt(a/psubt) sigma0: applied tensile stres a: Length of a surface crack psubt: crack tip radius
What is the equation for Plain strain fracture toughness?
Kic=Ysigmasqrt(pi*a)
unless specified: Y=1
simga: applied stress
a: Length of surface crack
What is the equation for design (or critical) stress?
sigmac=Kic/(Ysqrt(pia))
unless specified: Y=1
Kic: plain strain fracture toughness
a: length of surface crack
What type of metals typically experience DBTT?
BCC
Explain DBTT
Ductile to Brittle Transition with decreasing temperature
What is impact energy?
work done to fracture a test specimen
What are the components of an SN curve?
S: stress on y-axis
N: cycles to failure on x-axis
curves that don’t level off do not have a fatigue limit and will eventually fail due to fatigue
How to improve impact of fatigue?
Put compression on surface
What is the relationship between creep strain and temperature or stress?
If T<0.4Tm then creep strain is essentially negligible. If stress or temperature go up instantaneous deformation go up and time to rupture shortens. Slope of steady state creep rate increases.
epsilon dot represents what? What does the equation without T represent?
Steady state creep rate. Steady state creep rate at constant temperature.
What are the 4 things you should find from a phase diagram?
- # of phases & what they are
- composition
- amounts
- picture/pie chart
What are the -ites in order from strongest to weakest?
- martensite
- tempered martensite
- cementite
- bainite
- fine pearlite
- course pearlite
- spherodite
- ferrite
pearlite is ferrite + cementite
What are the two types of metals?
ferrous and non-ferrous
Are steel and cast iron ferrous or non-ferrous?
ferrous
What are the differences between steel and cast iron?
cast iron has more carbon (3-4.5 wt% C). Steel has <1.4 wt% C. Also, cast iron has graphite.
What distinguishes different types of cast iron?
shape of graphite
List all the non-ferrous metals along with their qualities
Al - low density, cheap, manufacturable Mg - really light, ignites easily Ti- light, strong, expensive, hard to machine Cu - excellent conductivity Refractories - good at high temperatures Noble metals - do not oxidize (rust)
What are all of the processing techniques?
Forging
Casting
a. Sand
b. Investment
Rolling (Hot/Cold)
Extrusion
Drawing
Power Processing
Welding
Should know what these looked like
What are the different types of annealing procedures?
- Normalizing
- Spherodizing
- Full Anneal
- Stress Relief
What is hardenabililty?
how easily a sample forms martensite
What is the test for hardenability?
Jominy End Quench Test
What is 1020?
low carbon steel
What is 4190?
tool steel
What is >10 wt% Cr?
stainless steel
What is 4310?
HSLA
What is the wt% C of 1020 steel?
0.2
