تأثیر بار اضافی بر رشد شکاف خستگی در چدن نادری: آزمایشات و شبیه سازی عددی

During operation, materials or engineering components are subjected to variable amplitude loading (service loadings), which influences the life time considerably. After chemical, morphological and mechanical characterization of nodular cast iron, systematic investigations of the fatigue crack growth behavior were studied under constant and variable amplitude loading. The results under constant amplitude loadings can be described well by the FORMAN/METTU equation (also known as NASGRO equation), whereby the fatigue crack growth behavior exhibits a dependence on the graphite microstructure. Under variable amplitude loading the experiments show that overloads with various overload ratios always exhibit acceleration effects. These acceleration effects affect the accuracy of life time predictions significantly. Hence, the calculation of the remaining service life based on different usual life time prediction models yields non-conservative results. Therefore, an extended strip yield model is applied, which is able to predict the observed crack growth acceleration after overloads. Finally the numerical results are compared with experiments.