Jan Exam Flashcards
What is the equation for secondary creep strain rate?
Strain rate = K*sress^n *e^(-Q/RT)
What temperature does strain rate occur?
T>0.4Tm
How can you find Q? Graphically.
Gradient of ln(strain rate) v 1/T
T in Kelvin
Gradient = -Q/R
How can you find n? Graphically
Gradient of ln(strain rate) v ln(stress)
Gradient = n
What is Larson Miller Parameter used for?
Extrapolation
What is the equation for LMP?
LMP = T(C+logtr)
Where tr = rupture lifetime (in hours)
C normally equals 20
How do you find LMP?
From a graph, tr can then be calculated from it.
How is creep strain related to time?
Strain = Strain rate * time
Is creep strain total strain?
NOOO!
Total strain = creep strain + steady state/instantaneous/primary
Normally given
How would i take 1.5x10^6 as a strain rate?
Make it 0.15x10-7 and use that value on the graph.
What type of brackets are used for directions?
Square for individual, triangular for family
What brackets are used for planes?
circle for individual and curved for family
How do you find interceptions of planes?
Planes given in miller indices,
Interception = 1/miller indices.
Note: if infinite then it doesnt touch that axis.
What is linear density?
Number of atoms centred on vector/length of vector
Note: number means throughout whole of cube in that direction.
What is planar density?
Number of atoms centred on plane/ Area of plane
How is a related to r in BCC
root3 a = 4r
How is a related to r in FCC
root2 a = 4r
What is the atomic packing factor?
Volume of atoms in cell / Volume of cell
Note: atoms volume = 4/3 Pi r^2
Volume of cell = a^3
What is the equation for theoretical density?
density = Number of atmos * Atomic mass / Volume of cell * Avogadros number
Note: number of atoms in FCC = 4 BCC=2
Avogadros Number = 6.02x10^23
What wt%C do Cast Irons have?
2.14 - 4.5% (after steels)
What are the types of cast iron?
Gray, nodular, white, malleable, compact graphite
How do you get pearlitic maleable cast iron?
Fast cooled hot white cast iron.
How do you get Ferritic maleable cast iron?
Slow cooled hot white cast iron
What does higher damping capacity do?
Reduce chatter
What type of castings are there?
Sand, Die, Investment, Continuous, Fabrication
What Aluminium alloys are heat treatable?
2, 6, 7
What Aluminium alloys are Strain hardened?
1, 3, 5, 8
What is precipitation hardening also called?
Age hardening
What is strength?
Max load at failure, highest stress
What is ductility?
Ability to deform
What is Hardness?
Resistance to deformation, indented test
What is stiffness?
Resistance to elastic deformation, stress/strain Youngs Modulus
What is the Ultimate strength?
Peak on curve before necking
How do you find the yield if it is unclear?
0.2% straight line same gradient
What is the area under a stress strain graph?
Toughness (impact energy that can be absorbed)
What is poissons ratio?
v = -lateral strain / logitudinal strain
= -delta diameter/diameter. / delta length/length.
What is bulk modulus?
K
To do with pressures on object
P=-K deltaV / V
What is shear modulus?
G
Torsion
torque = Gy
Where y = displaced angle
How is poissions ratio related to other moduli?
V = E/2G - 1
How is ductility measured?
Strain at failure
%EL = Lf - Lo /Lo
Or same with areas
What is engineering stress?
Original area used
What are point defects?
0D
Vacancies, Interstitials, Substitutionals, Frenkel, Shottky
What are line defects?
1D
Dislocations (screw,Edge)
What are planar defects?
Grain boundries, Stacking falts
What are bulk defects?
Pores, inclusions, cracks
Are defects useful?
They give a material its mechanical properties
So YEA!
always in materials
What is the AISI - SAE system?
XYWZ
where X = group of carbon steel
Y = Amount of alloying element
WZ = Carbon concentration (20 = 0.2%)
What are these parts of a phase diagram called?
alpha, gamma, Fe3C, Fe3c + alpha
In order,
Ferrite, Austenite, Cemetite, Pearlite
What are the 2 phase diagram reactions and what are they?
Eutectoid ( gamma - alpha +Fe3C)
Eutectic ( Liquid - gamma + Fe3C)
at what wt%C is a eutectoid steel?
0.76
What are the other steels in the phase diagram?
Hypoeutectiod, eutectoid, hypereutectoid
What are the WT%C of ferrite and cementite?
0.02% and 6.7%
How do you use the lever rule?
Amount of LHS weighting = RHS / Total length
Amount of RHS weighting = LHS / Total length
Limits are 0.02 for ferrite, 0.76 (proutectiod) austenite, 6.7 cementite
What are the compositions of the following microstructures? Hypoeutectiod, eutectoid, hypereutectoid
ferrite + Prelite
100% pearlite
cementite + pearlite
How do you find the composition of each phase?
draw straight line horizontally to the end of each phase, these will give you the wt% of one element, use this to find the other.
How is the strain energy release rate calculated?
G = stresspia / E
a = half the length of the crack
How do you calculate the critical stress?
= (2Eys/pi*a)^1/2
where ys = specific surface energy
How do you calculate the fracture toughness?
K = Ystressroot(pi*a)
if K > Critical toughness then it will fail. (critical toughness determined using critical strength)
Y= material constant.
How do you produce matensite?
Quenching: heating to above recrystalisation temp and cooled rapidly in water or oil.
It can then be temered to regain ductiity by heating to below recrystalisation temp and cooled slowly at room temp
What will Austenite turn into when cooled at different rates? From a non equilibrium phase digram.
Slow = Pearlite Medium = Bainite Fast = Martensite
How do you calculate the stress concentration factor?
Kt = (1 + 2a/b)
Measure of how much the stress is amplified
Where a = width and b = height of hole/crack
What to do when given t bars with fillet radius (stress concentrators)
find r/d,
look at graph to find Kt for given D/d (may need to interpolate)
finds stress using smaller d and force
Max stress = SCF * stress
What is the graph for cyclic loading?
Stress amplitude vs cycles to failure
How do you calculate the amplitude on cyclic loading?
half of (max stress - min stress)
How do you find mean stress?
max stress + min stress / 2
What type of question could we get for cyclic loading?
To find max and min stress,
Find equations for them using mean and amplitude,
Solve simultaneously
3 notes for phase diagrams
always give compositions of both elements in phase
when pre eutectic, phase grows in grain boundries (give compositions of these phases too)
Always draw straight line to either side if mixed phase. Useful for lever rule and wt%
What are the wt%C of the following metals?
Wrought Iron, Steel, Cast Iron
<6.7
How do you calculate the coefficient of thermal expansion?
strain = Alpha(T2-T1)
What is the bond energy and how do other factors change as it increases?
The energy to create or break a bond between atoms.
As Bond energy increases:
Melting temp increases, Coef of thermal exp decreases, Elastic modulus increases
What is the Hall-Patch Equation?
Yield strength = Stress. + Ky*d^-0.5
Where stress. and Ky are material constants
d = average grain diameter
