Biaxial Fatigue Testing and Simulation of Cruciform Sub-Structure

In this work, numerical simulations and experimental tests are performed to determine if it is possible to accurately predict the fatigue behaviour of a glass fibre reinforced polymer (GFRP) sub-structure, when fatigue data from a fatigue material database is used in combination with static properties of the actual material. Firstly an appropriate sub-structure is designed based on biaxial test specimens readily found in the literature. The main objective during the design phase is to produce a sub-structure where inter-fibre failure occurs in a typical wind turbine blade laminate when a prescribed biaxial constant amplitude load is applied. The designed sub-structure is tested in biaxial fatigue, and it is shown that there is no delamination in the ply-drops in the gauge zone and that first failure occurs in the gauge zone without cracks from the corners propagating into the gauge zone. This is achieved by using internal ply-drops and a cross-ply dominated lay-up. Lastly, a simulation of the fatigue test is conducted where the linear progressive strength degradation model FADAS (Fatigue Damage Simulator) algorithm is applied. The algorithm is applied to predict the progressive damage in the corners, because this influences the stress and strain field in the gauge zone.