Effect of adding a woven glass ply at the exit of the hole of CFRP laminates on delamination during drilling

Composite materials are increasingly used in the aeronautical field. The assembly of structures requires usually drilling of composite parts. Drilling of composite materials generates defects, mainly delamination at the exit of the hole. This major defect diminishes the structure strength. Delamination is directly related to the drilling thrust force. Minimizing this force reduces the defects. Adding a woven glass ply at the exit of the hole is found to be another adequate solution to reduce the defects. In this paper, the drilling of carbon/epoxy thick composite structures with a woven glass ply at the exit of the hole is considered. An analytical model is developed to determine for a given tool geometry the critical delamination forces as function of the number of non-drilled plies remaining beneath the tool. The results are validated experimentally. These results show that adding a woven glass ply at the exit of the hole reduces delamination.