13 - Generic solutions for reducing the likelihood of overstress and wearout failures

Abstract

The chapter presents generic solutions for reducing the risk of component failures, such as, improving reliability by a relative separation of the upper tail of the load distribution and the lower tail of the strength distribution; and by eliminating tensile residual stresses at the surface of components. The mechanisms of failure of components can be divided broadly into overstress failures, such as, brittle fracture, ductile fracture, yield, buckling, etc. and wear out failures, such as, fatigue, corrosion, stress-corrosion cracking, wear, creep, etc. Overstress failures occur when load exceeds strength. Conversely, wear out failures are characterized by a damage which accumulates irreversibly and does not disappear when load is removed. Once the damage tolerance limit is reached, the component fails. The chapter discusses how to increase the resistance against failures caused by excessive stresses; reduce the risk of failure by optimizing loading and avoiding unfavorable stress states; reduce the risk of failure due to excessive deformation; reduce the risk of failure by improving the resistance to fracture; reduce the risk of overstress failure by modifying the component geometry; reduce the risk of failure by mitigating the harmful effect of the environment; and it also presents generic methods for reducing wear out failures. The corrosion intensity is a function of the environment. Aggressive environments combined with low corrosion resistance cause expensive early-life corrosion failures. Methods increasing the corrosion resistance include cathodic protection, corrosion allowance, protective coatings, plastic or cement liners, use of corrosion resistant special alloys. Corrosion control can also be ensured by condition monitoring. The chapter also deals with improving the resistance against failures due to erosion and cavitations.