Question 1
a) Explain briefly if the following scenarios can be approximated as plane stress, plane strain or neither:
(i) A point inside the Hoover dam
(ii) An arbitrary point within a cubic casting of aluminium
(iii) A thin wafer of silicon used for a microchip experiencing thermal stress
b) (i) Based on the data given in the stress tensor below, determine the principal stresses acting on the component.
MPa
(ii) Produce a sketch of a Mohr’s circle to roughly confirm your answer is reasonable (this can be by hand or via computer drawing package).
Question 2
- A decorative cladding for a building situated next to a main road is constructed out of copper and zinc fused together. After a winter of heavy road salting the trim has started to corrode. Suggest a mechanism of corrosion and note which of the metals you expect to be corroding and why.
- A set of old stainless steel swimming pool steps need to be repaired by welding. A few months after the repair, corrosion is spotted next to the weld, however corrosion was never a problem before the repair. Suggest a mechanism of corrosion and why it is only now a problem.
- The instructions for a polymeric sealant designed for sealing plumbing equipment states “for indoor use only”. Suggest and describe a degradation mechanism in polymers that might be the reason for this limitation.
Question 3
- A cracked pipe is repaired using welding as schematically shown in figure 3. A large “scoop” of material is removed from the cracked region (figure 3b) and the resulting hole is filled with weld metal (figure 3c).
Figure 3
(i) Despite the intention being to improve the structural integrity of the pipe, welding is known to have a detrimental impact on structural integrity. Outline two specific considerations that must be made when taking into account the structural integrity of welds and briefly explain why they are significant.
(ii) For both considerations discussed above, explain how an engineer can measure and subsequently quantify their potential impact.
b) Shot peening is used to induce residual stress into the surface of a component:
(i) Explain briefly the process of shot peening, the nature of the residual stress field induced and why this might be beneficial to a component.
(ii) Describe a suitable process for measuring the residual stresses in a shot peened metal plate justifying your choice.
