Fatigue failure assessment of a short glass fibre reinforced polyamide 6.6 under mulitaxial loading

The fatigue bahaviour of a short glass fibre reinforced polyamide 6.6 (PA66-GF35) under multiaxial loading was investigated on hollow tubular specimens in the range of fatigue lives between 102 and 107 cycles. Fatigue experiments included pure tension, pure torsion, combined tension-torsion at different stress biaxiality ratios and phase-shifting angles between the stress components. Experiments were carried out with load ratio R=0 and R=-1 at room temperature as well as at 130°C. An extensive failure analysis was performed on the specimens to recognise the main damage mechanisms and failure modes via optical and scanning electron microscopy. The Tsai-Hill failure criterion, modified to take into account cyclic loading, was successfully implemented for fatigue behaviour assessment, using as strength parameters those obtained from cyclic off-axis tests from a previous investigation.