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A midsemester quiz for the aerospace materials lab (ase 224l) held in spring 1996. The quiz covers various topics related to materials science, including young's modulus, poisson's ratio, plastic strain, phase diagrams, deformation mechanisms, and polymers. Students are required to answer questions related to determining material properties, identifying phases, and explaining material behavior.
Typology: Quizzes
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a) Determine the Young’s modulus, E , and Poisson’s ratio, ν, of the material. [2]
b) Following yield (σ= σy), the plastic strain, εp, in the material was suspected of following the relation.
εp = (σy/E) (σ/σy) 1/N
Determine the exponent N from the following data. [3]
σ/σy 1 1.5 1.8 2.0 2. εp/εy 1 7.5 18.9 32.1 97.
c) If the material failed at σ/σy = 2.5, determine the toughness of the material. [3]
d) A particular structural application of the material requires a bar with a yield strength of 118 ksi. Determine the total strain that would have to be applied to the bar before it could be used. [2]
e) What is the name of the material characteristic that allowed the process in d) to be conducted. Explain how the characteristic is manifest at the microscale of the material. [3]
(kip)
DISPLACEMENT (in)
Load / deflection response (schematic)
range from 0.6 TM ≤ T ≤ 0.8 TM, where TM is the melting temperature of the alloy. Stresses are expected to range from 1 x 10-4 G ≤ σ ≤ 7 x 10-3 G, where G is the
shear modulus of the material.
(a) Identify which deformation mechanisms are dominant for the range of conditions given above. [2]
(b) Discuss the experiments you would need to conduct and the data reduction required in order to determine the constants A, α and the stress exponents for the secondary creep rates, ˙ε (^) s. [4]
(c) Explain why it would be advantageous to operate at lower stress levels rather than different temperatures. Determine the difference in rupture times from operating at the two extreme stress levels to assist your explanation. [4]
Plastic Flow
Elastic
Dislocation Creep
Diffusional Flow
Bulk Diffusion
Boundary Diffusion
5 - α/T
M
log σ/G
(b) Explain the difference in molecular structure between a thermoplastic and a thermosetting polymer and how it affects the creep compliance.. (4)
(c) Show that the relaxation modulus of the polymer represented by the combination of springs and dashpots shown below is :
E ( t ) = Eo + E 1 e − t / τ , τ =
η 1 E 1
η 1
(d) A sheet of the polymer is being clamped by a bolt which essentially imparts a
clamping stress to drop to 20% of its initial value? (3)
