On the evaluation of critical thrust for delamination-free drilling of composite laminates

The existing analytical models in the literature for estimating the critica l thrust force of the drill to avoid delamination of composite laminates du ring drilling assume the drill force as a point load on the laminate. Also, they are based on small deflection assumptions even while considering the pushing out of the last one or two plies at drill exit. In this paper, the effects of these two assumptions on the critical thrust value have been exa mined by taking an alternate assumption of a distributed thrust over the dr ill diameter, and large deformation of un-cut plies during drill exit. The effects of both these assumptions are calculated and analyzed separately.