Fatigue behavior of large cast components under variable amplitude loading with overloads

To reduce the weight and to increase the power as well as to enable the utilization of nodular cast iron components, e.g. for wind turbines and heavy industry parts, locally higher stresses need to be withstood by the material. This becomes crucial, when additional overloads influence the structure of thick-walled components causing high local elastic-plastic deformations. In this case, the cyclic, elastic-plastic material behavior and its development under cyclic loading are important points to be considered during component design. To assess the material's local elastic-plastic material behavior, strain-controlled fatigue tests were performed under alternating loading, Re = -1, with unnotched specimens removed from cast blocks as well as from a hub and a planet carrier of wind turbines, made of EN-GJS-400-18U-LT, EN-GJS-700-2, ADI-800 and ADI-900. To determine the influence of constant and variable amplitude loading on the elastic-plastic material behavior, fatigue tests were performed based on constant amplitude as well as on variable amplitude loading. For the fatigue tests under variable amplitude loading, two real load-time histories, which were derived from a measured load-time series from the base frame of the nacelle and the hub of a wind turbine, were used. In order to analyze the influence of an additional overload during usage, additional test series with maximum overloads of 0.5 and 1.0 % under pressure loading were embedded in the load sequence and the results compared to those without overload.