Evaluation of a novel approach to a delamination factor after drilling composite laminates using a core–saw drill

Drilling is the most commonly applied method for hole making of fiber-reinforced materials owing to the need for structure joining. Delamination is the most common defect during drilling because of the heterogeneity of both the fibers and the matrix. The delamination, in general, is an irregular shape and size, containing long and fine breaks and cracks at the exit of the drilled hole, especially in the drilling of carbon-fiber-reinforced plastic (CFRP). On the other hand, a core–saw drill is designed to reduce the threat of chip removal in drilling composite materials. Since the thrust force of core–saw drill is distributed toward the periphery, the core–saw drill allows a larger critical thrust force than the twist drill at the onset of delamination when drilling composite materials. The aim of this paper is to present a novel approach of the equivalent delamination factor (F ed) to characterize drilling-induced delamination using a core–saw drill and compare it with the adjusted delamination factor (F da) and the conventional delamination factor (F a). The experimental results indicated that the F ed obtained is considered suitable for characterizing delamination at the exit of a hole after drilling CFRP.