Flexural fatigue behaviour of UDGFRP experimental approach

Abstract

Prediction of the fatigue behaviour of a unidirectional glass fibre reinforced polymer (UDGRP) has been improved from the synthetic analysis of fatigue results concerning more than one thousand medium and long term tests. This program concerns epoxy-glass fibre systems processed using three classical techniques: filament winding, press moulding of prepreg, and pultrusion. The fatigue tests were performed by means of two kinds of bending test, i.e. three-point and compression bending. The superficial sample observation specified the very first damage nucleation and its propagation stages. Damage was measured by recording the evolution of the stiffness of the sample and the fatigue life was conventionally defined as N 10, i.e. the number of cycles corresponding to a 10% stiffness loss. The fatigue behaviour for all the batches was described by the same relationship: ϵ max = A − Blog N 10, where ϵ ax is the maximum imposed strain, A the extrapolated strain value giving 10% stiffness loss after only one cycle and B the slope of the fatigue curve (defined as relative strain decrease by decade of cycles). It appears that the material behaviour is first specific to the process itself. Filament winding was slightly better than press moulding and much better than pultrusion. Furthermore, in the case of materials processed by filament winding, the influence of both shear strength of the interface and toughness of the matrix was analysed.