For an engineering strain of 1, calculate percentage elongation (ductility) of the specimen?
100
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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
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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.
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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
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Poisson's ratio for metals, ceramics and polymers is in the range:
0\.15 < v
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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
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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
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What is diffusion
Mass transport by atomic motion
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Atoms tend to _____________ from regions of _____________ concentration to regions of _____________ concentration.
Migrate, high, low
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What is self-diffusion?
Migration of host atoms in pure metals
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What is the derivation of the equation relating the diffusion coefficients at two temperatures T1 and T2, given that:
D₂ = D₁exp \[-Qd/R(1/T2-1/T2)\]
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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
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Non-steady state diffusion is a function of:
Time and position
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Fick’s first law of diffusion is applicable to
Steady state diffusion
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What’s Fick’s second law of diffusion?
dC/dt = D d²C/dx²
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What's Fick’s first law of diffusion?
J = −D dC/dx
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What’s the relationship between the diffusion coefficient and temperature?
Increases with increasing temp
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What is interdiffusion?
Diffusion of atoms of one material into another material
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Diffusion rate of vacancy diffusion depends on
Number of vacancies, activation energy
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interstitial diffusion
smaller atoms diffuse between adjacent atoms, faster than vacancy diffusion
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Case hardening is an example of _________ diffusion
Interstitial
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case hardening
outer surface is hardened by diffusing carbon atoms into surface
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Doping
adding impurities to a semiconductor to increase conductivity
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Process of doping
P rich layers on surface
Heat it
Doped semiconductor regions
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Diffusion is faster for
open crystal structures, materials with secondary bonding, smaller diffusing atoms, lower density materials
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Tensile load (pulling)
If a specimen is being elongated or extended
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Compressive load (pushing)
Specimen is compressed or contracted
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Deformation
Change in dimension
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shear forces
Parallel to cross sectional area
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Plastic deformation
permanent change in shape by bending and folding
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Elastic deformation
material returns to original state when stress is removed
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