FATIGUE CRACK-GROWTH UNDER STATIONARY RANDOM LOAD

A stochastic model describing fatigue crack growth under stationary random loading is presented. The closure concept is applied to account for load interaction effects. The crack opening stress for a given loading cycle is estimated on the basis of the highest maximum and lowest trough observed in the n preceding cycles. It is shown that in this case some characteristic integral of crack length is normally distributed. This permits lifetime estimation at any prescribed reliability level. Examples illustrate the application of the proposed approach. It was shown that the lifetime estimates first increase abruptly with n and then tend asymptotically to some constant value. The life estimates based on the asymptotic value of n may prove to be non-conservative. The dependence of lifetimes determined at a prescribed reliability level on the applied stress, fracture toughness, Paris exponent m, and other parameters for some specific cases are given in graphical form.