Experimental and numerical investigations on push-out delamination in drilling of composite laminates

This study conducts experimental and numerical studies on the progressive damage occurring during the drilling of composite laminates. In particular, this work focuses on push-out delamination, which occurs at the interface around the drill-exit and is the most critical damage suffered during the drilling process. To investigate the damage progression mechanisms, penetration and interruption drilling tests are performed on composite laminate consisting of quasi-isotropic CFRP plies and fabric GFRP ply (bottom side). After drilling tests, the damage evolution is evaluated using X-ray computed tomography and optical microscopy. Based on the experimental results, a simplified simulation model is established, and damage progression simulation is performed using an explicit dynamic finite element method. The results show that the bending deformation in the bottom two plies triggers the propagation of push-out delamination. Therefore, the extent of delamination is significantly affected by the thickness and the material properties of the bottom plies.