A RELIABILITY-BASED MODEL TO PREDICT SCATTER IN FATIGUE-CRACK NUCLEATION LIFE

This paper investigates the scatter inherent in the early stages of fa tigue life. A probabilistic fatigue model is proposed which relates th e microstructural heterogeneity to the scatter in crack nucleation lif e. The crack nucleation life is defined as the number of cycles necess ary to develop a crack with a length equal to the grain size. The mode l assumes homogeneity at the level of the grain size. A fracture mecha nics-based microstructural model is used to describe the response of t he grains. The primitive random variables which drive crack nucleation are identified and recent developments recorded in the literature are used to describe their statistical characteristics. First order relia bility methods are used to predict the statistical distribution of fat igue crack nucleation life. Comparisons are made with trends in experi mental observations.