Complex stress state effect on fatigue life of GRP laminates.part I, experimental

In structural applications of thin-wall, box beam constructions with composites, the effect of complex stress states is not properly taken into account in determining operational life and fatigue response in general, due either to misconceptions or lack of experimental data and theoretical models. Results from a recent research project, presented here in two parts, aim to contribute to the better understanding of fatigue behaviour of GRP laminates under complex in-plane stress states. An initial estimate on the effect of neglecting shear and transverse normal stresses in fatigue life calculations is provided, based on experimental data and theoretical considerations. It is concluded that in structural GRP laminates, shear and transverse normal stresses have an important contribution in reducing operational life, irrespective of their magnitude, usually small compared to axial normal stresses.