Delamination is the major concern during drilling of composite laminates. Delamination, in addition to reducing the structural integrity of the laminate, also results in poor assembly tolerance and has the potential for long-term performance deterioration. Drilling-induced delamination occurs both at the entrance and at the exit planes. This paper presents an analysis of delamination during drilling. The analysis uses a fracture mechanics approach in which the opening-mode delamination fracture toughness, a material parameter, is used with a plate model of the laminate. The analysis predicts an optimal thrust force (defined as the minimum force above which delamination is initiated) as a function of drilled hole depth. Good agreement is achieved with data obtained from drilling carbon fiber-epoxy laminates. An advantage of the model is that it can predict varying degrees of delamination for other materials, such as glass fiber-epoxy, and for hybrid composites. In addition, the optimal thrust force for no delamination can be used to control a drilling machine with thrust force feedback for maximizing productivity.

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