1. Indicate briefly how the following affect fatigue life:
a. A good surface finish
b. The presence of a rivet hole
c. A significant mean tensile stress
d. A corrosive atmosphere
2. The next diagrams show a pulley block used to deploy an underwater platform from an offshore exploration rig. There are two modes of use: (a) when lowering or raising the platform off the side of the rig, (b) when slewing the platform over the deck of the rig. After about 200 deployments, the bolt broke and the platform was lost overboard. Where do you think the fracture occurred? Would you categorize the fracture as low-cycle or high-cycle fatigue? Support your answer by an approximate calculation. The bending moment at which a circular cross-section starts to yield is given by the standard equation
The steel of the bolt had a yield strength of 540 MN m–2. How would you modify the design to ensure that the connection between the lifting eye and the pulley block is less likely to fail by fatigue?
(a) Schematic of pulley block when lowering or raising. The crane exerts a straight pull along the axis of the lifting eye.
(b) Schematic of pulley block when slewing. The crane now exerts an oblique pull on the lifting eye.
(c) Details of lifting eye.
(d) Forces acting on the bolt when slewing.
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