Influence of specimen preparation by machining on the failure of polymer matrix off-axis tensile coupons

Milling is a usual operation to obtain composite coupons for mechanical tests. However, the machining of composite materials using cutting tools leads to high temperatures and machined surface damage that will tend to reduce their mechanical performances. This study presents an investigation of the influence of cutting parameters on the damage level and mechanical response of off-axis glass/epoxy unidirectional coupons machined by side milling. The analysis of cut surface roughness and micrographic observations reveals the primary importance of the relative orientation of the fibres with respect to the cutting direction. An analysis based on design of experiments underlines the influence of the cutting parameters and cutting edge geometry on the ultimate tensile stresses of the off-axis coupons. The results show the importance of the cutting configuration and fibre orientation on the mechanical performances. Two parameters have been defined to quantify the cut surface damages and relate it to the decrease of failure stress. A thorough statistical analysis is also included to separate significant from non-significant results in this study.