Experimental Investigation and Modelling of Fatigue Behaviour of Nodular Cast Iron for Wind Turbine Applications

The majority of modern wind turbine components, such as rotor hubs, tubular adapters, main frames and axles are made of a nodular cast iron. Its specific shape of the graphite in the ferritic microstructure acts as the crack arrester and lowers the stress intensity in front of the crack, which makes it an appropriate material for such cyclic loaded structures. This paper presents an experimental and numerical study on four different types of the nodular cast iron EN-GJS-400-18-LT. The experimental procedure includes symmetrical and unsymmetrical strain controlled tests on the cylindrical specimens as well as crack initiation and propagation tests on the compact tension specimens. Different loading regimes are applied, and monitoring of the crack length during the tests is performed by an optical system. Within the framework of numerical investigations an efficient algorithm for modelling of cyclic plasticity is proposed. The material model is based on multi-component forms of isotropic and kinematic hardening variables. Experimental results show that size and distribution of the nodules has no significant influence on material hardening but they play a great role in the crack initiation and propagation process. Moreover, wrong choice of material type could significantly reduce the component's lifetime. This is especially evident on the results obtained under higher loading amplitudes.