Fatigue Crack Growth In Nodular Cast Iron - Influences Of Graphite Spherical Size And Variable Amplitude Loading

Investigations of constant and variable amplitude loading, including a variety of overloads, were carried out experimentally as well as numerically in order to characterize the fatigue crack growth behaviour of nodular cast iron with a ferritic matrix. Under constant cyclic loading the crack growth rate, which depends on the graphite size can be described well by the NASGRO equation. The mean distance between the graphite particles and the shape factor also influence the fracture behaviour. The experimental investigations show that overloads yield to acceleration effects in fatigue crack growth. The calculation of the a-N curves based on different usual life prediction models yields non-conservative results. Therefore, a modified strip yield model is presented which allows the prediction of the crack growth acceleration after overloads in nodular cast iron.