Effect of milled notches on the strength of open hole, filled holes, single and double lap shear CFRP tension coupons

Splitting is the presence of a long, thin matrix crack observed in laminates stacked with unidirectional plies. The importance of splitting has been highlighted several times in the literature to explain failure scenarios of open and, more rarely, filled hole CFRP coupon specimens. This failure mode also seems to play an important role in the increase of residual strength after fatigue that is sometimes observed in such specimens. In this study, a machining process is used to mill notches at the boundary of holes for open and filled holes, and for single and double lap shear specimens. These notches mimics the effects of splitting and a significant increase of the quasi-static tensile strength (up to + 20%) is observed in open/ filled hole coupons and for double lap shear specimens. However, for single lap-shear specimens, the results are within the dispersion of the experimental results or lower.