Question

Discuss how the fatigue resistance of a part or material can be improved.

Its for 5 marks so please no short answers.

Answer 1

Methods to improve fatigue resistance are :-

1. Change material. Changes in the materials used in parts can also improve fatigue life. For example, parts can be made from better fatigue rated metals. Complete replacement and redesign of parts can also reduce if not eliminate fatigue problems. Thus helicopter rotor blades and propellers in metal are being replaced by composite equivalents. They are not only lighter, but also much more resistant to fatigue. They are more expensive, but the extra cost is amply repaid by their greater integrity, since loss of a rotor blade usually leads to total loss of the aircraft. A similar argument has been made for replacement of metal fuselages, wings and tails of aircraft.
2. Induce residual stresses Peening a surface can reduce such tensile stresses and create compressive residual stress, which prevents crack initiation.
3. Deep cryogenic treatment. The use of Deep Cryogenic treatment has been shown to increase resistance to fatigue failure. Springs used in industry, auto racing and firearms have been shown to last up to six times longer when treated. Heat checking, which is a form of thermal cyclic fatigue has been greatly delayed
4. Re-profiling. Changing the shape of a stress concentration such as a hole or cutout may be used to extend the life of a component.