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##### Page 1
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CARLETON
UNIVERSITY
FINAL
EXAMINA TION
December 2002
DURATI~N: 3
HOURS
No. of Students: 85
Department
Name
& Course
Number:
Mechanical & Aerospace Engineering AERO 3700
~
';;;~~D;-:~' ,.&_~...
~lnstructor(s)
Professor M. McDill
UTHORIZED MEMORANDA
Calculators
Students
MUST
count
thenumber
of pages
in thisexamination
question
paper
before
beginning
to write,
and
report
any
discrepancy
immediately
to a proctor.
Thisquestion
paper
has
6 pages.
Thisexamination
question
paper
MAYbe taken
from
theexamination
room.
tothisquestion
paper,
students
require:
an
examination
booklet yes
L
no-
a Scantron
sheet
yes
-noL
All ques~ions
are of equal value. An equation sheetis attached.
1
a. The yield strength of polycrystalline low-carbon steel is 622 MPa when the average grain
diameter is 180 ~m {ASTM #2) and 663 MPa (ASTM #8) when the average grain diameter
is,
22. 5 ~m. Use the Hall- Petch relationship to determine the yield strength of the steel
if the
average grain diameter is 11.2 ~m. (ASTM #10).
1
b. Why are smaller grained metals preferred for applications at lower temperaturesand larger
grained materials preferred for applications at higher temperatures?
2.
Telescopesare instruments composedof mirrors, lensesand electro-optical devices used to
collect electromagnetic radiation from distant objects in space.
The resolution of a telescope
is very sensitive to the optical alignment of the various components. Clearly the structure
supporting the active devices must be both stable and stiff. From a materials selection
perspective,telescopesin orbiting platforms or on satellitespresent
a challengmgapplication.
a.
List four requirements for the materials used in the support structure of a telescope
used in a spaceapplication.
b.
Using your four requirements as a guide, briefly discuss the usefulness of metals,
ceramics and polymers in this application.
c.
Is there a material that has the potential to satisfy all four requirements?
.,

##### Page 2
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Mechanical and Aerospace Engineering AERO 3700
2
Final Exam, December 2002
3.
2024 Al alloys have aoo"ut
4 W
/0 Cu andareusedin aircraft structures.2219 Al alloys containnearl
y
6 w/o Cu and are used in spaceboosterand fuel tanks. A portion of the AI-Cu phase diagram is
shown below.
a.
Choose
the description below (i to iv) thatbest
describes
the microstructure
thatwould be
found
in a 4 w/o Cu alloy in theT6 condition. The specification for the Al inthe T6 condition reads,
"solution heat-treatedplus artificially aged."
b.
SUl2l2os~
the phasediagram canbe used for the 2219 alloy. It is heatedto 550°C and held for
a period of time and thenquenchedand aged. Choosethe description below (i to iv) that best
describes the microstructure that would be found after aging.
c.
Would a T6 treatment normally be used with an AI-Cu alloy? Explain your answer.
i.
supersaturated
K with separate
grains of e
ii.
supersaturated
K
iii.
K with a fine precipitate of e
iv.
K with a fine precipitate of e plus coarse grains of e
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