Early fatigue crack growth as the damage accumulation process

A probabilistic approach to modeling of the initial stage of fatigue crack growth is suggested based on the concepts of continuum damage mechanics. Th e material is presented as a set of microstructural elements with randomly distributed properties. Both the grains and intergranular boundaries are co nsidered as the elements of microstructure. The parameters of resistance of each element to damage accumulation are considered as random variables. Th ese parameters are distributed among the elements independently that allows to model the damage process in polycrystalline materials. The damage measu re depends on the characteristic normal and tangential stresses in order to take into account the tensile and shear fracture modes for each element of microstructure. It is assumed that a nucleus of a crack is initially prese nt near the body surface as a single completely ruptured element. The final damage of an element is considered as the crack advancement. The crack is modelled as a sequence of ruptured grains for the transgranular fracture, a nd as a sequence of couples of neighboring ruptured grains when the intergr anular rupture is considered. Numerical simulation is performed to illustra te feasibility of the proposed model. In particular, non-planar crack propa gation, blunting, kinking and branching of cracks at the early stage is dem onstrated. The non-monotonous pattern of the short crack growth process is observed. Statistical scattering of the current crack size and the crack gr owth rate as functions of the cycle number and the crack depth is studied. (C) 2001 Elsevier Science Ltd. All rights reserved.