FATIGUE DAMAGE STAGES IN UNIDIRECTIONAL GLASS-FIBER EPOXY COMPOSITES - IDENTIFICATION THROUGH ACOUSTIC-EMISSION TECHNIQUE

Fatigue damage in composites occurs in stages. Before attempting to estimate quantitatively the extent of cumulative damage which is necessary to estimate the fatigue life of these materials, it is useful to understand the basic process in relation to the significance of the stages of damage. The acoustic emission (AE) technique, with its on-line monitoring capability, has the potential to be the most suitable candidate as a tool for this purpose. Experimental investigations were carried out on unidirectional glass-fibre-reinforced plastic (GFRP) composite coupons to explore the feasibility of identifying the damage stages using acoustic emission. The coupons were subjected to constant-amplitude load cycles with continuous AE monitoring. The results of the experiments show three distinct stages of damage before the final failure of coupons; these stages could be correlated to different failure mechanisms.