Fatigue life prediction of composite structures under constant amplitude loading

An approach to construct the stress (or load) vs. cycles curve for composite structures under constant amplitude loading is presented. The approach is based on the assumption that the cycles to failure are a function of the probability of failure during any given cycle. In this first investigation, this probability of failure during any cycle is assumed to be constant and equal to the probability of failure obtained from static test results and the associated statistically quantified scatter. Expressions for the cycles to failure as a function of R ratio are derived. These expressions do not require any curve fitting and do not involve any experimentally determined parameters. The fatigue predictions do not require any fatigue tests for calibration. Comparisons to several test cases found in the literature show this first simple model to be very promising.