Assessment of service loads and material influence on the lifetime of thick-walled nodular cast iron components

Abstract

To reduce weight and increase power as well as utilisation of nodular cast iron components, e.g. for wind turbines and heavy industry parts, locally higher strength need to be withstood by the material. This becomes crucial when additional overloads, coming from a storm, a grid loss during operation or a misuse, influence the structure of thick-walled components, causing high local elastic-plastic deformations. In this case, the cyclic, elastic-plastic material behaviour and its development under cyclic loading are important and have to be considered during component design.To assess the material’s local elastic-plastic material behaviour under the influence of overloads, strain-controlled fatigue tests, under constant and variable amplitude loading, were performed under alternating loading, R = −1, with unnotched specimens removed from cast blocks, a main frame and two planet carriers of wind turbines made from EN-GJS-400-18U-LT, EN-GJS-700-2, ADI-800 and ADI-900.By using two different load-time histories with a bulky and a more linear form, derived from local hot spots at a wind turbine’s hub and a main frame, in a first step, the lightweighting potential could be determined by comparing the S-N curves for constant and variable amplitude loading. In order to analyse the influence of an additional overload during usage, in additional test series, a maximum compressive overload of 0.5 and 1.0% total strain under tensile loading was included in the load sequence and the results compared with those without an overload.