Morphological characteristics and formation mechanisms of the UD-CFRP drill exit-damages

Carbon fiber-reinforced plastic (CFRP) is used widely in many industries. During drilling CFRP, exit drill-induced defects such as burrs and delamination are easy to occur. In the existing model, the crack zone is assumed as a circle or an ellipse, and concrete forming process of the delamination and the burrs does not be truly involved. In this study, the formation mechanisms of the delamination and the burrs are analyzed based on the analytical model and the experimental observation. The results indicate that the critical thrust force only reflects the vulnerability of the crack, but cannot determine the size of the crack. The critical deflection of the fibers tip corresponding to the interlaminar crack extension point determines the size of crack. The burrs appear in four fundamental types.