AEROSPACE MATERIALS LABORATORY
(ASE 324L)
Fall 1998
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
Th
(circle one)
1.
Four different materials (a, b, c, d) were subjected to the strain history shown
below. The maximum strain (  max ) for materials a, b, c and d was 0.1, 2.0, 2.0 and
0.1%, respectively. A portion of the response of each material is also shown below.
(a) Complete the response curves for each material (with lines and arrows).
Explain your chosen response. (8)
(b) Name each of the responses and indicate to which class of materials each
response might belong. (4)
(c) Based on (b), explain what events are occurring at the microstructural level to
produce the observed responses. (8)


(a)
0.1%

 
max
(b)
2.0%

(c)

(d)
Time
s
0.1%

2.
The phase diagram of the alloys that can be made from two materials (A and B) is
shown below. Consider an alloy made of 45 kg of A and 55 kg of B.
(a) Identify the phases that this alloy can have, indicating the range of
temperatures over which each phase can exist. (5)
(b) Determine the composition and relative amounts of each phase that is present
at 400˚. (4)
(c) Suppose you were considering making an alloy with 10% B. Would it be
possible to alter its strength characteristics by solution treating it? Explain. (3)
(d) What alloys of A and B could form supersaturated solutions and be age
hardened? (3)
3.
A new high temperature metal alloy is being considered for use as a turbine blade.
It is anticipated that the service temperatures will exceed 0.5TM, the melting temperature
of the alloy.
(a) Indicate what experiments you would conduct to determine the effect of stress
and temperature on the mechanical behavior of the alloy in this temperature
regime. (4)
(b) Suppose that you determine that temperature has the following effect on the
secondary creep rate ( Ýs ):
Ýs  Ae (Q / RT)
Derive an expression for the Larson Miller parameter and explain how it is used to
predict creep rupture times in service, based on short-term, high temperature
experiments at stress levels that differ from the design values. (5)
(c) Explain what is meant by power law creep and how you would go about
determining the power law exponent, n. (3)
(d) Make a rough sketch of a deformation mechanism map and indicate how you
would use it to determine the ranges of stress and temperature levels for the
experiments in (b). (3)
4.
(a) Polymers are generally amorphous, but can contain regions of crystallinity
which often appear as spherulites. Explain how amorphous and crystalline
regions are structured on the molecular scale and indicate how this affects the
respective volume vs. temperature responses of a fully amorphous, a fully
crystalline and a partially crystalline polymer. (6)
(b) The tensile relaxation modulus of a gasket is to be modeled by the springs and
dashpot in the arrangement shown below. The tensile relaxation modulus of a
Maxwell element is
E  E0 e t / 
By considering the response of the combination of elements shown below to a
step strain, show that the tensile relaxation modulus of the gasket is
E  E1  E0 e t / 
and identify the glassy and rubbery moduli of the adhesive. (4)
(c) The gasket has inner and outer radii of 1.75 and 2.0 in., respectively. It is
subjected to a strain of 0.1% in service and it no longer seals when the load it
transmits is less than 60 lb. Find how long the gasket will remain in effective
service if E0  50.0ksi, E1  0.5ksi and   2yrs. . (5)