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Aerospace Materials Lab Midsemester Quiz - Spring 1993, Quizzes of Aerospace Engineering

The midsemester quiz for the aerospace materials laboratory (ase 224l) course held in spring 1993. The quiz covers various topics related to materials testing, phase diagrams, and material behavior under different conditions. Students are required to answer questions related to choosing the appropriate load cell for tensile tests, determining elastic behavior, calculating material toughness, identifying phases in the iron/carbon phase diagram, and discussing deformation mechanisms. The quiz also includes questions about the atomic packing structure of different phases and the strengthening mechanisms of certain materials.

Typology: Quizzes

Pre 2010

Uploaded on 08/26/2009

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AEROSPACE MATERIALS LABORATORY
(ASE 224L)
Spring 1993 – Midsemester Quiz – Tuesday, March 23rd
2:00 – 4:00 p.m.
This is a closed book exam.
There are four questions to be answered.
The number of points assigned to each question is shown in [ ].
NAME:
Section: T W Th (Circle One)
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AEROSPACE MATERIALS LABORATORY

(ASE 224L)

Spring 1993 – Midsemester Quiz – Tuesday, March 23rd

2:00 – 4:00 p.m.

This is a closed book exam. There are four questions to be answered. The number of points assigned to each question is shown in [ ].

NAME:

Section: T W Th (Circle One)

  1. You have been asked to test a new Titanium alloy. It's Young's modulus and Poisson's ratio expected to be 150 GPa and 0.3, respectively. The anticipated yield strength, ultimate tensile strength and failure strain are 1 GPa, 1.2 GPa and 0.2, respectively. The specimens will have a 10 mm diameter with a 50 mm long gage section.

(a) You have a choice of a 50 kN or a 100 kN load cell with which to conduct tensile tests to failure. Indicate, with quantifiable explanation, which one you would choose.[2]

(b) Determine the displacement range that a diametrical extensometer would have in order to capture the complete elastic behavior of the material. [4]

(c) Determine the toughness of the material if the stress/strain response was bilinear with a change in slope at the yield point and the ultimate tensile strength occurred at the failure strain. [3]

(d) Could the strength of the alloy be improved by cold working? Explain your answer by referring to dislocation-based models of plastic deformation. Indicate how it is that dislocations can cause strain hardening. [6]

  1. A turbine blade will be used in operating conditions where the temperatures will range from 0.6 T (^) M ≤ 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/TM

log σ/G

  1. (a) What is the material property that is used to judge whether or not a polymer is likely to exhibit viscoelastic behavior? Explain how you would determine the property without conducting any creep or relaxation experiments. [3]

(b) The combination of springs and dashpot shown below is used to represent the creep of a polymer. Show that the differential stress/strain law for the material is

d ε dt

  • k η ε = kg + k kg

 σ η

kg

d σ dt

[5]

(c) The creep of the model developed in (b) due to a constant stress, σo, is

ε ( t ) = σ o kg

  • σ o k

(^1 −^ e − t^ /^ τ),^ τ =^ n k

Determine the creep compliance of the material and explain whether or not this represents a thermoset material. [2]

k

k η g