The influence of interlaminar stresses on fatigue behaviour of notched composite laminates

The influence of the interlaminar stresses on the fatigue behaviour of composite laminates is studied. The present paper is comprised of experimental results and comparison with theoretical results on the delamination onset and propagation. Numerical results are obtained by a specialized computer code which has shown the points where the high intensity of the interlaminar stress tensor components can produce a delamination. Several tension-tension fatigue tests have been performed on angle-ply and cross-ply centrally holed composite specimens which present the major sensitivity to the interlaminar stresses in order to verify the onset and the propagation of delaminations in the same points revealed by the static analysis. For the identification of the presence of delaminations an ultrasonic NDI equipment in the form of reflection has been utilized; this system provides a 3D positioning of the delaminations inside the laminates. The experimental results are in good agreement with the theoretical previsions for both the stacking sequences.