Fatigue Life Prediction Based on the Advanced Fatigue Crack Growth Model and the Monte-Carlo Simulation Method

Abstract

It is well-known that loss of the structural stability due to propagation of the dominant crack is one of the main sources of fatigue failures. Therefore, computationally feasible fatigue crack growth model is essential for advanced fatigue life analysis. Appropriate model should be able to calculate the time required for crack to grow: from the initial crack of any size to the final critical length; in any structure; under applied variable loading. The UniGrow two-parameter total driving force was proposed ten years ago. Since then, the fatigue crack growth model based on it, was enhanced with a set of memory rules and resulted in a sophisticated fatigue crack growth software package which was extensively validated on the basis of available experimental data. Nevertheless, in its previous form the UniGrow model had several serious limitations: it was not able to model the fatigue crack growth under plane-strain conditions; the Neuber rule was the only method used for elastic-plastic stress-strain analysis; the fatigue crack growth prediction was limited to macro-cracks and the variability of the material response to cyclic loading has not been considered. In addition to these shortcomings, there were no preferred method for estimation of the material block size , which is one of the main parameters required for the analysis. Therefore, further modeling and validation of the UniGrow concept were required before it could be coupled with the "Monte-Carlo" simulation method. The main research goal pursued in this work was to improve and remove limitations of the existing fatigue crack growth model and to combine this model with "Monte-Carlo" simulations. Such combination enables the assessment of the reliability of predicted fatigue lives. Thus, the result of this work is an extensive probabilistic fatigue crack growth model, which is able to perform the analysis of structures in the plane-strain or plane-stress condition. Comprehensive set of the fatigue crack growth data for aluminum and steel alloys generated under the constant and variable amplitude loading was used for the validation.