Reliability of Lifetime Prediction for Composite Materials under Variable Amplitude Loading

Kurzfassung

The success in the use of composite materials requires apart from cost-effective manufacturing a well-founded and reliable lifetime prediction. Since most composite structures are subjected to variable amplitude loading, the applied lifetime prediction models have to consider numerous different parameters and their various effects are usually difficult to separate from each other. An extensive investigation focuses on the influence of a number of these parameters on the properties of a lifetime prediction methodology commonly used for the lifetime prediction of GFRP or CFRP laminates under variable amplitude loading. Regardless of the specific properties of one lifetime prediction model used, the process of lifetime prediction consists of several components all affecting the obtained results. Generally this process is divided into four tasks executed in a sequential manner. These are a load spectra analysis using a load cycle counting algorithm, the establishment and statistical evaluation of S-N curves and their interpolation in a constant life diagram and finally the application of a damage accumulation rule. For any of these components various formulations are possible and each of them can change significantly the obtained results. The exact knowledge about these effects is a fundamental basis for reliable lifetime predictions and their comparison. This work is based on a modular software tool which is still under development. Each module represents one single task of the aforementioned process and enables the possibility to compare various lifetime prediction models in an easy and standardized manner. This first of a sequel of papers deals with the influence of different cycle counting methods on the predicted fatigue life.