PROBABILISTIC MODEL OF EARLY FATIGUE-CRACK GROWTH

A model is developed in this paper to describe the nucleation and earl y growth of fatigue cracks. Polycrystalline materials are modelled as a set of elements (grains) with random properties. It is assumed that the resistance to damage of neighboring elements is mutually independe nt and follows the same probability distribution, except for the eleme nts situated near the surface whose resistance is lower and which are subjected to higher scattering. Damage accumulation in each element du e to cyclic loading is considered, and an element is treated as ruptur ed when a critical damage level is attained; then the ruptured element is included in the cracked domain. The finite element technique is ap plied to realize the modelling. Numerical results exhibit all the prin cipal features of early fatigue crack growth such as nonmonotonous cha nge of crack growth rates, statistical scatter of crack dimensions and growth rates, and stabilization of the process when a considerable nu mber of grains enter the cracked domain. (C) 1998 Elsevier Science Lim ited.