Investigation of hole morphology and tool wear in 3D pierce-fabric carbon/carbon composites during drilling

Abstract

ABSTRACT 3D Pierce Fabric (PF) Carbon/Carbon (C/C) composites are well established in the defense sector due to their extreme strength, stiffness, and thermal stability at elevated temperatures as well as to withstand high bending loads. Reinforcements are generally oriented in the Z-direction to enhance the composite resistance against delamination and through-thickness cracking. However, the coexistence of woven carbon fabric and Z-reinforcement makes machining challenging. The present study investigates the hole morphology, internal damage & dimensional accuracy, and tool wear during drilling of 3D PF C/C composites. Drilling was carried out perpendicular and parallel to the Z-reinforcement. Internal damage and hole geometry were analyzed using conventional CT and high-resolution micro-CT, while surface morphology and delamination behavior were examined using a digital microscope, while material removal mechanisms and tool wear were analyzed using SEM. Results indicate that drilling perpendicular to the Z-reinforcement produces a stable hole geometry with minimum internal damage and maintains hole diameters within range of 20.1495 mm to 20.1627 mm, whereas drilling parallel to the Z-reinforcement results in larger hole diameters ranging from 20.1639 mm to 20.1986 mm, due to fiber pull-out, matrix cracking, and unstable cutting. Material removal is dominated by brittle matrix fragmentation in perpendicular drilling and fiber fracture with bundle debonding in parallel drilling. Tool wear is mainly governed by abrasive chipping.