Investigating the VHCF of composite materials using new testing methods and a new fatigue damage model

Kurzfassung

Composite materials are used in several fatigue-relevant applications nowadays and characteristic fatigue data is needed. However, composites have to be told apart from metals and so have to be the fatigue behaviors. Unfortunately, the established testing and simulation methods are not suitable for composites. However, two new experimental approaches providing accelerated VHCF testing are presented. A resonant and a non-resonant setup are used. For the first setup the resonant behavior of specimen and test stand are used to load GFRP tubes at roughly 600Hz and a load ratio of R=-1. The second approach utilizes a specifically designed four-point bending test running at 50-80 Hz. Fatigue data including stiffness degradation, evaluation of crack density and delamination are gained up to 10 8 cycles. Both methods reach testing frequencies beyond classic testing methods and thus allow time efficient VHCF testing. First results for fatigue testing with glass-fiber-reinforced plastics are presented. Furthermore, a new layer-based fatigue damage model (FDM) is presented, which is physically motivated by using an approach that relates energy dissipated under quasi-static and the energy dissipated under cyclic loading. The Puck failure criterion is used and has been extended with degradation factors for analyzing discontinuous damage. Load interactions as well as nonlinear damage accumulation are taken into account. Degradation of stiffness and strength can be calculated for every single layer over the simulated lifetime.