Exit delamination at the material interface in drilling of CFRP/metal stack

Carbon fiber reinforced polymer (CFRP)/metal stacks have the merit of a high tensile strength-to-weight ratio with the CFRP and high compressive strength with the metal. To use CFRP as a material of structural component in industries, drilling is required to make holes for joining with other parts. In drilling, compared to the component built with CFRP only, the CFRP/metal stacks are less vulnerable to the exit-ply delamination caused by the thrust force because the metal part of the stack plays a role of a back-up plate. However, the delamination frequently occurs at the CFRP-metal interface, even though the thrust force is too small to generate delamination. Existing experimental studies reported that cutting torque as well as thrust force results in exit-ply delamination in CFRP/metal stack drilling, but the mechanism of delamination behavior at the CFRP-metal interface is not established. This study proposes a theoretical model to investigate the exit-ply delamination at the interface between CFRP and metal caused by the cutting torque. Using the model, we calculated the allowable feed limit to prevent cutting torque-induced exit-ply delamination. Through the drilling experiments, the proposed model was validated.