Analysing the onset of multiple site damage at mechanical joints

A detailed analysis has been performed on the onset of multiple site damage at mechanical joints. The crack initiation is analysed based on non-linear stress analyses and the crack closure model. It has been found that the stress-strain response at the joint can have a stabilised linear relation under fatigue loading even if considerable plastic yield has occurred. This makes it possible to analyse the post yield multiple crack initiation based on fracture mechanics solutions for the crack growth in a residual stress field. Weight function method has been used to solve stress intensity factors and Green's functions for the crack growth analyses according to a strip yield crack closure solution. In this analysis, the small crack behaviour as well as the post yield effect have been accounted for. Intrinsic material parameters have been extensively used so that the method is not limited to the specified problems. Together with the crack growth analyses, a probabilistic model has been developed to account for uncertainties in initial flaw, stochastic crack propagation, geometrical inconsistency, as well as variation in the fatigue load. According to the probabilistic solution, important information about the onset of multiple site damage, e.g. the probability of crack occurrence, and the probability of crack break-through etc., are predicted as a function of the stress and the construction of joint. One example is provided to illustrate the procedure and to highlight problems in dealing with the onset of multiple site damages at mechanical joints.