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Aerospace Materials Lab Midsemester Quiz - Spring 1996, Quizzes of Aerospace Engineering

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

Pre 2010

Uploaded on 08/30/2009

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AEROSPACE MATERIALS LABORATORY
(ASE 224L)
Spring 1996 Midsemester Quiz 2:00—4:00 pm WRW 102
Please attempt all four questions. The points
assigned to each question are shown in ( ).
This is a closed notes/homework/book exam.
Space for your answers is provided in this
booklet.
NAME:
Lab section meets on T W (circle one)
pf3
pf4
pf5

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AEROSPACE MATERIALS LABORATORY

(ASE 224L)

Spring 1996 Midsemester Quiz 2:00—4:00 pm WRW 102

Please attempt all four questions. The points

assigned to each question are shown in ( ).

This is a closed notes/homework/book exam.

Space for your answers is provided in this

booklet.

NAME:

Lab section meets on T W (circle one)

  1. The load/deflection response of a structural alloy is shown below. It was obtained from a specimen having a rectangular gage cross section that was 0.5 in. wide and 0.25 in. thick. The gage length was 2.0 in. The thickness of the specimen at yield was 0.2497 in.

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]

LOAD

(kip)

DISPLACEMENT (in)

Load / deflection response (schematic)

  1. A turbine blade will be used in operating conditions where the temperatures will

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

Core Diffusion ε = Aσ e

Bulk Diffusion

Boundary Diffusion

5 - α/T

ε = Aσ e

  • α/T

T/T

M

log σ/G

  1. (a) Describe how you would use a temperature cabinet, a thermocouple and a transducer for measuring displacements to distinguish between an amorphous and a crystalline polymer. Indicate what response you would measure and how it would differ for the two materials. (3).

(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 et / τ , τ =

η 1 E 1

E 0

E 1

η 1

(d) A sheet of the polymer is being clamped by a bolt which essentially imparts a

constant, compressive strain, ε 0 to the sheet. How long will it take for the

clamping stress to drop to 20% of its initial value? (3)