Question 3
a) Explain the characteristic signs you would expect to see on the surface of
metallic materials that had failed by brittle, ductile, and fatigue fractures
respectively. Indicate if different features would be seen for different materials.
(12 marks)
b) The fatigue life for a certain alloy at stress levels of $\sigma_1$, $\sigma_2$, and $\sigma_3$ is 400, 1,200,
and 4,000 cycles respectively. If a component of this material is subjected to 100
cycles of $\sigma_1$ and 800 cycles of $\sigma_2$, estimate the remaining lifetime in association
with cyclic stresses at a level of $\sigma_3$. Discuss the assumptions in this approach.
note:
$\sum_{i=1}^{k} \frac{n_i}{N_i} = C$
(8 marks)
Total Marks = 20
