Analytical model for delamination of CFRP during drilling of CFRP/metal stacks

CFRP/metal stacks are widely used in aeronautical field. Drilling such stack composite in single shot is still challenging because of different machining properties between CFRP and metal. Delamination often occurs at the exit of the composite which can affect the strength of the composite components. Elastic deformation of CFRP and metal plate occurs in drilling process and furtherly affects the drilling character and critical delamination conditions. The aim of this paper is to study the delamination during drilling of CFRP/metal stacks with deformation of CFRP and metal plate. Analytical mechanical models are proposed to predict critical thrust force of CFRP in the drilling process for two stacking sequences, respectively. The elastic deformation of CFRP and metal plate and the local deformation of uncut CFRP laminate in the cutting zone are taken into consideration. The values of critical thrust force and the influences of the deformation of CFRP and metal plate on critical thrust force are obtained based on the solutions of the model. A series of punching experiments with accurate remained uncut plies is conducted to verify the rationality of the proposed models. The results indicate that the prediction of the proposed model shows a close correlation with the experiment measurements.