Paper 7: Designing to Prevent Fatigue Failures in Service

Abstract

Despite intensive research, failures in service still occur too frequently, and in normal environments most service failures are caused by metal fatigue of some component. The basic mechanism of fatigue failure is examined, indicating that in many cases the failure of a component is dependent more on the cyclic stress required to grow a fatigue crack than on that required to initiate a crack. In such cases, the plain fatigue strength of a material alone may be of little use to the designer, and additional knowledge is required to effect the efficient design of a real component or structure. The problems of variable-amplitude stress cycles and service loadings, notches, crack propagation characteristics, fretting, joints and environment are discussed in some detail, and the concept of designing for a flawed material is proposed.