1993 Volume 42 Issue 472 Pages 29-34
A procedure to evaluate residual life under cyclic combined loadings was established for a given initial state of distributed small cracks. Distributed cracks at the initial stage were modeled as straight-line cracks by using an image-processing technique. The algorithm for the analysis of the crack growth after the initial stage was constructed by taking account of both modes of the propagation as a single crack and the coalescence between propagating cracks. Fatigue tests under combined axialtorsional loadings with constant and variable amplitudes were also conducted using cyclindrical specimens of pure copper with circumferential blunt notches. The fatigue life was correlated with the equivalent plastic strain range. When Compared for the same value of the parameter, the fatigue life became longer with increasing shear component in the stress state at the notch root, while no significant difference was observed between two loading modes of constant and variable stress amplitudes. The fatigue life defined by the formation of crack with a specific length was evaluated based on the proposed procedure. The predicted life almost coincided with the experimental data. Cracking morphology was also simulated by using the present model to show good correspondence with experimental observations.
