Analytical and Numerical Analysis of Mixed-Mode I/II Fatigue Crack Growth Rate and Path Prediction

Abstract

Mode I fracture mechanics have been relatively mature, but mixed-mode fracture mechanics present challenges under different loading angles. Since most engineering materials are subjected to inclined cracks and/or multiaxial loading, there is a well-justified need to establish a solid understanding of their fracture behavior under mixed modes. This thesis aims to study how to predict mixed-mode fatigue crack propagation under various loading angles for the compact tension shear specimen of 7075-T651 aluminum alloy. In this study, both analytical and finite element approaches were used to predict the expected fatigue crack growth rate and direction for various models. Equivalent stress intensity factor was analyzed considering the most common approaches such as Irwin, Tanaka, Richard, and Demir criterion. A comparison between them was performed taking into account how to examine which fatigue crack model of mixed-mode can better predict fatigue crack growth rate close to the experimental data obtained from the literature. To achieve this, predicted equivalent stress intensity factor (concerning the experimental stress intensity factor) for each of the four models for 30°, 45°, and 60° loading angles were considered. Tanaka criterion is in good agreement with the experimental results up to 45° loading angle. Although the Demir model is expected to provide higher accuracy for higher mode mixity cases, its prediction is close to the experimental data even for the case of loading angle equal to both 30° and 45° . Overall, Demir’s models predict crack propagation rate close to the selected experimental data based on the overall consistent performance