A Computational Methodology for Fatigue Life Prediction Under Multiaxial Non-Proportional Loading 2001-01-0837

A methodology for predicting the fatigue initiation life in metals experiencing multiaxial non-proportional loading is presented. The methodology utilizes nonlinear finite-element analysis to determine the stress distribution of the loaded component. This distribution is used in conjunction with a physically based damage law to determine the cycles to failure. The damage law is based on the fatigue prediction method introduced by Dang Van [1], and further developed by Papadopoulos [2] and Morel [3]. The fatigue damage initiation is treated as the persistent crystalline slip phenomenon taking place on the order of a grain or few grains. The damage variable is chosen to be the accumulated plastic strain at this scale. The initiation life is determined when the damage variable reaches a critical value. The developed methodology is applicable to both in-phase and out-of-phase loading, without any empirical adjustment parameter. In order to validate the methodology, the predictions are compared with the experimental results on tension-torsion of thin walled steel tubes by Fatemi and Stephens [4]. Conservative predictions within a factor of 4 for proportional loading and slightly over a factor of 4 for non-proportional loading are obtained. Thus, this methodology shows promise as a practical tool that could be used in durability predictions of components experiencing complex loading conditions