Fatigue Life Analysis of Specimens Subjected to Infrequent Severe Loading using a Nonlinear Kinematic Hardening Cyclic Plasticity Model

For engineering structures subjected to cyclic load, fatigue failure normally occurs at geometrical discontinuities such as holes and notches. In aircraft structures, such locations may experience occasional severe loading that can cause appreciable local plastic deformation. This poses a significant challenge to fatigue life modelling. For such locations subjected to variable amplitude loading of a large number of cycles, the numerical analysis of fatigue life requires an accurate and robust model for cyclic plasticity, in order to reliably determine the stress and strain response. In this paper, we explore the potential of a nonlinear kinematic hardening model in improving fatigue life analysis. The work is motivated by the inability of an existing strain-life model to capture the difference in fatigue damages caused by an unclipped and clipped service load spectrum. Preliminary results show that the strain-life method based on the nonlinear kinematic hardening model was able to qualitatively demonstrate the trend in fatigue life for two critical locations analysed, and it was able to give much improved quantitative prediction for one location. Further work is under way to verify the model against more test data and to improve its capability in dealing with material cyclic softening or hardening behaviour.