AEROSPACE MATERIALS LABORATORY
(ASE 324L)
Fall 2002
Midsemester Quiz
3-4 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. A rod of a material with a 0.5-in diameter and a 2-in gage length yields at a load of
15708 lb and an extension of 0.008 in. The Poisson’s ratio of the material is 0.25.
(a) Find the tensile modulus, yield strength and change in diameter of the rod when it
yields. (4)
105  
  , where E is the Young’s
(b) The plastic strain in the rod is given by  p 
E  y 
n
modulus, n  10 and  y is the yield strength. Find the permanent strain in the
material after it has been loaded to 23,562 lb and then unloaded. (4)
(c) Determine the yield strength of the material upon reloading. (2)
(d) Explain how yielding and strain hardening occur on the basis of dislocation
models. (5)
2. The 5000 series aluminum alloys have magnesium as the alloying element. The
phase diagram for the alloys is shown below. Consider a 5456 alloy which has 8%
weight % Mg.
(a) At what temperature does the alloy start to melt? When is melting complete? (2)
(b) Describe what phases are formed during an equilibrium cool from 500˚C to room
temperature. (3)
(c) What are the relative amounts of  and  at 100˚C? (6)
(d) Why does the relative amount of the  phase not vary during the cooling below
275˚C? (2)
(e) A solution treatment consists of quenching from the aluminum rich solid solution to
room temperature. What microstructure would you expect the alloy to have? (2)
3. A casing for a jet engine requires a series of bolts to operate at temperatures that are
more than 50% of the melting temperature of the bolt material. There is a concern
that the loads in the bolts will relax over time.
(a) Describe the series of experiments that you would conduct to characterize the
creep resistance of the material at different stress and temperature levels. (5)
(b) The bolts will be operating in a stress/temperature regime where dislocation creep
dominates. In that case, the secondary creep rate for a fixed temperature is,
Ýs  B n , where stress is in psi and time is in hrs.

Determine how long it will take the bolts to relax to 60% of the initial stress if the
tensile modulus of the material is 30x106 psi, the initial stress is 4000 psi, n  5 and
26
B  10 . (5)
(c) In another application, rods of the material are subjected to constant tensile loads
at temperatures greater than 50% of the melting temperature. Describe what
experiments would need to be conducted to determine the Larson Miller parameter
P  T[C  log t R ] at different stress levels. How would you determine the material
constant C ? (5)
4. A new polymeric adhesive has been developed and you have been given the task of
determining its glass transition. The material can be produced in any shape, but you
only have a temperature cabinet and extensometer available to you.
(a) Describe how you would determine the glass transition of the material. Show a
schematic plot of the data obtained and indicate all the important properties that can
be extracted from the plot. In addition, indicate how the glass transition is used for
design purposes. (5)
(b) The experiment in (a) reveals that the structure of the new polymer is entirely
amorphous. Describe how the material deforms at the molecular level at each of the
stages you outlined in the plot in (a). (5)
(c) Other tests on the material have determined that the material’s shear compliance
follows the response of a Kelvin element, where the shear creep
(1 e  t /  )
compliance J 
. A single lap joint with two metal (rigid) adherends joined
G
by the adhesive is subjected to a constant load P  10000 lb. The length, thickness
and width of the adhesive layer are 2.0, 0.02 and 0.5 inches, respectively. The spring
stiffness and viscosity of the elements that represent the shear behavior of the
5
6
adhesive are G  10 psi and   10 psi.yrs . If the relative displacement of the
adherends is limited to   0.0016 inches, determine when the joint will fail by
excessive deformation. (5)
[Note] Creep and relaxation in shear can be handled the same way that they are handled
in tension.