Mechanistic insights into microscale surface morphology evolution of CF/PEEK under coupled effects of cutting mode and cutting edge radius

Carbon-fiber-reinforced thermoplastic composites (CFRTPs) have attracted growing attention as potential alternatives to conventional thermoset composites owing to their good damage tolerance, fatigue resistance, and repairability. However, the characteristics of anisotropy and heterogeneity, compounded by the plasticity of thermoplastic matrix results in more complex chip formation and surface evolution during machining. This paper aims to elucidate the surface-morphology formation mechanism of CF/PEEK under the influence of tool wear. Firstly, a micro-scale finite element model for orthogonal cutting is developed, and it is validated by cutting-force predictions with errors of less than 9% for orthogonal cutting at different fiber orientations. Then, two equivalent cutting modes are introduced to capture the local cutting behavior of randomly distributed fibers. Meanwhile, the quantitative study of the effect of cutting-edge radius (CER) on material removal and surface formation under the two modes is conducted through finite element (FE) analysis. The numerical simulations reveal that the cutting plane shifts upward as CER increases from 2 μm to 6 μm. The phenomenon renders the fiber failure mode evolves from compressive-dominated to a coupled compressive - shear mode and alters the failure mode of matrix. Under tool wear conditions, the fiber-dominated cutting mode tends to produce fiber debris covered by smeared matrix on the machined surface, whereas the matrix-dominated mode tends to leave residual fibers on the machined surface. The mechanisms provide the basis for understanding material removal behavior and the evolution of machined surface morphology in CF/PEEK under the different tool wear state.