Studied by 58 peopleThe given stress-strain graph represents?
Elastic then plastic deformation
What does the figure represent?
Simple compression
Which material has the highest toughness?
Material 2
For an engineering strain of 1, calculate percentage elongation (ductility) of the specimen?
100
A specimen of copper having a rectangular cross-section 15.2 mm X 19.1 mm is pulled in tension with 44,500 N force, producing only elastic deformation. Calculate the resulting strain. ( Elastic modulus of copper = 110 GPa)
1.39 x 10^-3
Ductility is the amount of plastic deformation at failure.
From the given graph below, determine which line represent a material with high ductility and which line represent a material with low ductility.
Blue line: Low ductility.
Green line: High ductility.
For some metal alloy, the true stress of 345 MPa produces a plastic true strain of 0.02. How much does a specimen of this material elongate when true stress of 415 MPa is applied if the original length is 500 mm? Assume a value of 0.22 for the strain-hardening exponent, n.
23.7mm
Poisson's ratio for metals, ceramics and polymers is in the range:
0.15 < v <= 0.5
Deformation of a sample to an engineering strain of 2 means that the sample is ___________ its original length.
A. Half
B. Twice
C. Three times
D. 2% longer than
Three times
What best describes the figure?
A. Not an example of diffusion
B. Left: before diffusion, right: after diffusion
C. Left: after diffusion, right: before diffusion
D. None of the above
Left: before diffusion; right: after diffusion
What is diffusion
Mass transport by atomic motion
Atoms tend to _____________ from regions of _____________ concentration to regions of _____________ concentration.
Migrate, high, low
What is self-diffusion?
Migration of host atoms in pure metals
What is the derivation of the equation relating the diffusion coefficients at two temperatures T1 and T2, given that:
D₂ = D₁exp [-Qd/R(1/T2-1/T2)]
At 300°C the diffusion coefficient and activation energy for Cu in Si are
D₁ (300°C) = 7.8 × 10⁻⁻¹¹ m²/s
Qd = 41.5 kJ/mol
Compute the diffusion coefficient D₂ at 400°C.
28.46 × 10⁻⁻¹¹ m²/s
Non-steady state diffusion is a function of:
Time and position
Fick’s first law of diffusion is applicable to
Steady state diffusion
What’s Fick’s second law of diffusion?
dC/dt = D d²C/dx²
What's Fick’s first law of diffusion?
J = −D dC/dx
What’s the relationship between the diffusion coefficient and temperature?
Increases with increasing temp
What is interdiffusion?
Diffusion of atoms of one material into another material
Diffusion rate of vacancy diffusion depends on
Number of vacancies, activation energy
interstitial diffusion
smaller atoms diffuse between adjacent atoms, faster than vacancy diffusion
Case hardening is an example of _________ diffusion
Interstitial
case hardening
outer surface is hardened by diffusing carbon atoms into surface
Doping
adding impurities to a semiconductor to increase conductivity
Process of doping
P rich layers on surface
Heat it
Doped semiconductor regions
Diffusion is faster for
open crystal structures, materials with secondary bonding, smaller diffusing atoms, lower density materials
Tensile load (pulling)
If a specimen is being elongated or extended
Compressive load (pushing)
Specimen is compressed or contracted
Deformation
Change in dimension
shear forces
Parallel to cross sectional area
Plastic deformation
permanent change in shape by bending and folding
Elastic deformation
material returns to original state when stress is removed
Common states of stress
Simple tension, torsion, simple compression, bi-axial tension, hydrostatic compression
Yield strength
point where the material begins to plastically deform
Toughness
the ability of a material to resist fracture
Hardness
resistance to localized surface deformation and compressive stresses
Resilience
Ability of a material to store energy
Ductility
amount of plastic deformation at failure
Engineering stress
tensile, shear
Engineering strain
tensile, lateral, shear
Percent elongation
the total percent increase in length of a specimen during the tensile test
Dislocation
A defect where atoms are misaligned around it
Edge dislocation
extra half plane of atoms inserted into a crystal structure
Dislocation line
The line where dislocations happen
Screw dislocation
lattice plane shifts similar to a spiral staircase
Burgers vector
measure of lattice distortion
Twin boundary
a reflection of atom positions across the twin plane
Solidification
Result of casting molten material
Grain boundaries
Regions between grains (crystals)
Point defects
vacancy, interstitial atoms, substitutional atoms
Vacancies are
vacant atomic sites
Dislocations move when
Stresses are applied
A catalyst ____________ the rate is a chemical reaction without being consumed
Increases
Dislocation types include
Edge, screw, and mixed
two diffusion mechanisms
vacancy and interstitial
The applied mechanical force is normalized to
Stress
The degree of deformation is normalized to
strain
Elastic deformation is
nonpermanent and reversible
Plastic deformation is
permanent and nonrecoverable
Stiffness
a material's resistance to elastic deformation
Strength
A materials resistance to plastic deformation
In an optical microscope, grain boundaries appear as white lines after the surface is prepared by etching. T/F
false
According for Fick’s first law, the concentration of diffusing species is a function of both time and position. T/F
false
D_interstitial << D_substitutional
T/F
false
In edge dislocation, burger’s vector is perpendicular to dislocation line. T/F
true
Diffusion coefficient _________ with increasing temperature
increases
What are the interfacial defects?
twin boundaries, grain boundaries, stacking faults
I can observe individual atoms using an optical microscope. T/F
false
What’s an example to processing using diffusion
case hardening
Interstitial diffusion is more rapid than vacancy diffusion. T/F
true
Equiaxed grains are
Roughly the same dimension in all directions
Columnar grains are
grains elongated in one direction
Rate of diffusion is __________ of time
independent
Diffusion is ____________ of time
dependent
What are the 5 interfacial defects?
external surfaces, phase boundaries, optical boundaries, twin boundaries, stacking faults
Note
Flashcard