Prediction of component life by application of fatigue crack growth knowledge

The concept of fatigue-crack propagation is discussed as it relates to life prediction. Since the use of propagation concepts assumes the presence of a minimum detectable initial flaw size this concept is discussed as it relates to the fatigue process. The relative roles of fatigue-crack initiation and propagation are presented. The acquisition of data is discussed and is then followed by a brief discussion of the variables that influence fatigue-crack propagation. A detailed discussion of the development of fatigue-crack growth ‘laws’ is then presented. These are then generalized to three forms, viz.: da/dN = C 1(S a) (1) da/dN = C 2S(a) n (2) da/dN = C 3f(K) n (3) Examples of the use of these crack growth ‘laws’ and the knowledge of fracture mechanics then is presented to illustrate the application of fatigue-crack growth concepts to: Predict life; establish greater reliability; select materials: improve design; establish inspection and maintenance intervals. The paper is concluded with a brief discussion of the needs for further knowledge and understanding to aid the science and engineering community in better utilization of engineering materials.