Materials for engineering, 3rd Edition - (Malestrom)

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Materials for engineering
Chapter 4
1. Silicon carbide and silicon nitride have respective thermal expansion
coefficients (0–1000 °C) of 4.5 × 10 –6 and 3.0 × 10 –6 K –1 , and thermal
conductivities (at 100 °C) of 125 and 20 W m –1 K –1 respectively.
Discuss their relative ability to withstand thermal shock.
2. A ceramic of Young’s modulus 200 GPa and effective surface energy
for fracture of 40 J m –2 contains a largest flaw 100 µm in size. If its
thermal expansion coefficient is 3 × 10 –6 K –1 over a substantial range of
temperature, estimate the maximum temperature change which the
ceramic, in the form of a bar, can withstand if its ends are held fixed
while the bar is cooled.
[Answer: 470 K]
3. Pores of diameter 5 µm are sealed in a glass under nitrogen at a pressure
of 8 × 10 4 Pa and the glass is then annealed in vacuum. Assuming that
nitrogen is completely insoluble in glass, determine the final (equilibrium)
pore size if the surface energy of the glass is 0.3 J m –2 .
[Answer: 2.8 µm].
4. The measured strengths of a certain ceramic are believed to follow the
Weibull distribution. From an extensive series of tests on identical
specimens the probability of surviving a stress of 700 MPa is estimated
to be 0.9 and that of surviving 900 MPa, 0.1. Determine the Weibull
modulus for the ceramic and the design stress for a 99% survival
probability for a ceramic component having a volume 10 times as great
as the volume of the specimens tested in establishing the above survival
probabilities.
[Answer: m = 12.275; 479 MPa]
5. A concrete casting is of Young’s modulus 50 GPa. When normally
prepared it contains voids of diameter up to 1 mm; if the void size were
reduced to a maximum of 15 µm in size, what change in tensile fracture
stress might be expected if the fracture surface energy were 1 J m –2 ?
[Answer: About + 40 MPa]
6. Calculate the value of Young’s modulus of concrete containing the
following volume fractions of aggregate (a) 0.45; (b) 0.6 and (c) 0.75.
[Answer: 48.4 GPa; 58.4 GPa; 73.6 GPa].
7. Outline the basic chemistry of the microstructural changes occurring
during the setting and hardening of Ordinary Portland cement.
Chapter 5
1. What properties do you expect in covalently bonded solids? How do
you account for the differences in mechanical behaviour between
polythene and diamond in both of which the carbon atoms are covalently
bound?