Effect of Cutting Edge Radius on CFRP Machining Mechanism with Pressure-Dependent Matrix Yielding

Cutting edge radius (CER) strongly affects force generation and surface integrity during carbon fiber reinforced polymer (CFRP) machining. However, because the local stress state in cutting zone varies with fiber orientation (FO), CER effect cannot be fully understood unless the pressure-sensitive response of the polymer matrix is considered. In this study, a novel micromechanical finite element model incorporating a modified Drucker-Prager constitutive law for the matrix is developed to study how CER affects material removal and surface generation in CFRP machining. The model is validated against measured cutting forces, machined surface topography and chip morphology, and predicts these responses more accurately than a pressure-independent Mises model. The results show that, as CER increases during cutting along fibers, matrix removal changes from shear band-dominated failure to compression crushing, while fiber removal changes from segment-type separation to complete crushing. Despite this transition, the machined surface remains smooth, and the surface roughness and the depth of subsurface damage increase only mildly. In contrast, when cutting against fibers, increasing CER changes matrix removal from tensile splitting to bulk fracture, and fiber removal from bundle bending fracture to compression crushing. This transition causes the surface profile to evolve from saw-teeth to irregular cavities and leads to a non-monotonic change in surface integrity. These results explain why a moderate CER can outperform a sharper edge in against-fiber cutting and indicate that CER optimization in CFRP machining should be FO-dependent.