Mech 473 Homework Assignment # 3 (total marks)
1. You graduate from UVic and are hired by an American defense (DoD) contractor
to place a one-foot diameter microsatellite into low earth orbit. The satellite will
contain delicate electronic equipment that will send and receive radio signals from
the earth. Design the shell within which the electronic equipment will be
contained. What properties will be required and what kind of materials might be
considered. (1)
2. The hull of the space shuttle consists of ceramic tiles bonded to an aluminum
skin. Discuss the design requirements of the shuttle hull that led to the use of this
combination of materials. What problems in producing the hull might be
designers and manufacturers have faced. (1)
3. Aluminum has a density of 2,7 g/cm3. Suppose you would like to produce a
composite material based on aluminum having a density of 1.5 g/cm3. Design
Design a material that would have this density. Would introducing beads of
polyethylene or hollow glass spheres, which have a density of 0.95, into the
aluminum be a likely possibility. Explain. (1)
4. Explain why aluminum alloys containing more than about 17% Mg are not used.
Assume that the  phase is an intermetallic compound and a eutectic structure is
produced. (1)
5. Based on their phase diagrams, which of the following three alloys would be most
suited for thixocasting? Explain your answer using their respective phase
diagrams. (2)
a) Al—12%Si
b) Al-1%Cu
c) Al-10%Mg
6. Suppose a 24-in long round bar is to support a load of 400 lbs without any
permanent deformation. Calculate the minimum diameter of the bar if it is made
of 6061-T6 aluminum alloy. Also calculate the weight of the bar and the
approximate cost. Pricing is typically based on the LME as per this link.
http://www.lme.co.uk/aluminiumalloy.asp (1)
7. Compare the percentage increase in the yield strength of commercially pure
annealed aluminum and its 1100-H18 alloy and explain the difference. (1)
8. Calculate the density of a cemented carbide, or cermet, based on a titanium matrix
if the composite contains 50 wt% WC, 22 wt% TaC and 14 wt% TiC. (See
Asklande & Phule, example problem 16-2 4th edition or 17-2 5th edition for
densities). (2)
9. An electrical contact material is produced by first making a porous tungsten
compact that weighs 125 g. Liquid silver is introduced into the compact. Careful
measurements indicate that 105 g of silver is infiltrated. The final density of the
composite is 13.8 g/cm3. Calculate the volume fraction of the original compact
that had interconnected porosity and the volume fraction that is closed porosity
(no silver infiltration). (2)
10. A polyester matrix with a tensile strength of 13,000 psi is reinforced with Al2O3
fibers having a tensile strength of 300,000 psi. What vol% fibers must be added
to insure that the fibers carry 75% of the applied load? (1)
11. A 0.01-cm-thick sheet of a polymer with a modulus of elasticity of 0.7 x 10exp(6)
psi is sandwiched between two 4-mm-thick sheets of glass with a modulus of
elasticity of 12 x 10 exp(6) psi. Calculate the modulus of elasticity of the
composite parallel and perpendicular to the sheets. (2)
12. The company that you are working for welds aluminum parts together using the
GMAW (MIG) process. Currently, they are using CO2 gas to protect the
aluminum during the welding process. However, the CO2 gas is too cold and
leaves a rough finish on the welds. What gas would you choose to improve the
finish on the welds? Why would you choose this particular gas? (1)
13. Stainless steels can suffer from “weld decay”. What is it and what two methods
can be used to eliminate it? (2)
14. Submerged-arc welding is used for the high-output welding of large steel panels
(such as ship decks) in the flat position. Describe the Submerged-Arc Welding
process. (1)