Study of drilling-induced defects for CFRP composites using new criteria

Drilling carbon fiber reinforced polymer (CFRP) composites is liable to generate serious defects including burrs, tearing, delamination, fiber pullouts and matrix degradation because of their inherent anisotropy in mechanical properties. A comprehensive analysis of the drilling-induced damage for CFRP composites plays a vital role in accurate evaluation of machined hole quality and in assessment of utilized tool performance. The present paper aims to propose a series of adjusted damage criteria allowing a reliable quantification of extents of the most critical defects in drilling CFRP laminates including burrs, tearing and delamination. To verify the applicability of the proposed evaluation criteria, a number of drilling tests were performed on T800/X850 CFRP laminates using three types of drills including brad spur drills, twist drills and dagger drills. The superficial drilling-induced defects residing around the hole periphery were examined by a digital microscope and the interlaminar delamination was characterized using a high-frequency scanning acoustic microscope (SAM). The comparative effectiveness of specialized drill bits in drilling CFRP laminates was evaluated by means of the newly-developed damage criteria. The obtained results highlight the feasibility of the proposed evaluation method in quantifying the drilling-induced defects of CFRP laminates and in distinguishing the cutting performance between utilized drill bits.