Analysis of material removal behavior and damage mechanism at hole exit in drilling high-toughness CF/PEEK composites

Abstract

At the hole exit when drilling thermoplastic composites, the weakly constrained fibers tend to deform, making them difficult to remove under the cutting of the main cutting-edge and the margin-edge. Additionally, tough matrix deforms without breaking, leading to a complex material removal process and damage behavior at hole exit. This study establishes a microscopic model that describes the removal state of brittle fibers and a ductile matrix under weak constraints. It reveals the material removal process and damage mechanism at hole exit in drilling CF/PEEK composites during sequential cutting by the main cutting-edge and margin-edge at low feed rates (f < 0.1 mm/r). Both simulation and experimental results indicate that, due to the high toughness of the matrix, the out-of-plane deformation caused by the main cutting-edge and the initial cracks have almost no direct correlation with the damage at the hole exit. Instead, the subsurface bending fracture of fibers and the mode III crack propagation induced by the margin-edge cutting directly lead to the formation of final damage. The prediction error of damage depth is <8 %. Based on the model, the study analyzes furtherly the potential mechanism by which damage at hole exit in drilling thermoplastic composites decreases with increasing feed rates.