Fatigue crack propagation under variable amplitude loading

Abstract

In this thesis, the use of crack growth rate data and analytical retardation models in predicting crack growth under variable amplitude loading is reviewed. The effective stress model developed by willenborg, et al. is described in detail, including the mathematical formulation. Comparison of test data and predictions for various loading programs are shown in figures. All tests are carried out in an MTS fatigue testing machine with a maximum capacity of 10 tons.During each test, cycling is interrupted periodically to measure crack length (with a Gaertner Travelling Microscope, X10). and to note the associated number of applied cycles. Compact tension specimen made of 2024-T4 aluminum alloy, are used throughout the tests. All tests are performed under ambient laboratory conditions.Eleven specimen are used to obtaine the experimental data. The results of the experimental program are used to review existing crack growth prediction models. In the logarithmic scale, crack growth rate vs. stress intensity factor range are plotted.