An examination of the effects from surface texture on the strength of fiber reinforced plastics

Surface texture and process defects resulting from net-shape machining of Fiber Reinforced Plastics (FRPs) are often ignored in a design analysis of component parts. The authors recently proposed a mathematical model which defines the effects of surface texture on the strength of engineering components in terms of an effective stress concentration factor ((K) over bar(t)). In this study, a verification of the proposed model for FRP materials is presented using results from a comprehensive experimental analysis on the flexure strength of graphite/epoxy and graphite/bismaleimide laminates. The effects of surface texture resulting from three methods of machining were evaluated using this new approach. The proposed model was also compared with the predictive capabilities of existing theoretical models in the evaluation of the experimental data. It was Found that the proposed model successfully predicted the reduction in flexure strength of FRP laminates resulting from net-shape machining over a large range in surface quality. Hence, results from this study indicate that the (K) over bar(t) offers a new design tool which can be used to account for the effects of surface texture on the strength of FRP components.