TWO‐STAGE‐MODEL FOR THE PROGNOSIS OF FATIGUE LIFE: APPLICATION TO BUTT WELDS

Abstract

This paper presents a Two‐Stage‐Model to determine the fatigue life. The model follows the distinction between the crack initiation and the crack propagation according to the phenomenological background. The first stage uses the local notch‐strain concept to predict the number of cycles for crack initiation Ni considering the cyclic material behaviour as well as the load‐time history. The second stage calculates the crack propagation based on a linear‐elastic fracture mechanics‐approach. Using the X‐FEM‐Method in combination with cyclic loading, an arbitrary, solution‐dependent crack path was achieved to determine the number of cycles for propagation Np. The Two‐Stage‐Model was applied to butt welds to determine the total fatigue life Nf. The study investigated the ability of the model to consider the influence of the weld geometry. The results are presented by means of SN‐Curves for initiation life, propagation life and total fatigue life and compared to experimental results.