Fatigue life reduction of GFRP composites due to delamination associated with the introduction of functional discontinuities

This paper reports on an experimental investigation into the fatigue life of Glass Fibre Reinforced Polymer (GFRP) when essential design discontinuities are introduced to a GFRP part to enable correct function. Specifically, the impact of high speed drilled holes on fatigue life is investigated. Fatigue life is a critical mechanical property, in particular, for industrial applications where both minimal weight and high reliability are sought. The paper investigates the impact of high speed drilling parameters on the delamination created around the hole, and subsequently on the static strength and fatigue life of GFRP composite laminates. Delamination damage in GFRP specimens is monitored using novel Acoustic Emission (AE) and image processing techniques. The progress of delamination under fatigue testing is used to predict GFRP mechanical performance and associated GFRP mechanical properties are proposed. What follows is an outline of the experimental method used. First, the extent of delamination after high speed drilling was measured in both unidirectional and woven GFRP specimens under different feed rate and cutting speed parameters. Quasi-static three point bending tests were then performed to investigate the effect of delamination on strength and to assist the determination of appropriate fatigue load magnitudes. Then, three point fatigue bending tests were completed. In this step, Acoustic Emission and image processing techniques were applied simultaneously. Experimental results indicated that drilling parameters have negligible effects on the static strength of GFRP specimens, however, the fatigue life of GFRP specimens varied significantly with the changes of drilling parameters. The experimental results also showed that AE and image processing techniques produced consistent data, offering a validation to the data itself and to indicating that both techniques have merit when completing experiments of this type more generally to determine the mechanical behavior (and associated mechanical properties) of specimens.