Mechanics of machining carbon fiber reinforced polymer

Carbon fiber reinforced polymers (CFRPs) are widely used in aerospace, automotive, and other high-performance structures because of high specific stiffness and strength. Although CFRP components are often manufactured near net shape, machining remains essential for assembly and repair. However, CFRP machining involves fiber orientation (FO)- and layup-dependent material removal under high strain rates, leading to variations in cutting forces and machining-induced damage that can degrade dimensional accuracy, surface integrity, and structural reliability. This dissertation develops physics-based models to understand CFRP machining mechanics by addressing three key questions in CFRP machining: (1) how cutting strain rate interacts with FO to govern material removal in unidirectional (UD) CFRP, (2) how cutting force varies in multidirectional (MD) CFRP with different FO combinations, and (3) how material removal and surface generation can be simulated accurately for contrasting FOs. First, a laminate-scale analytical model is developed for UD CFRP cutting. The model explicitly describes the cutting stress and strain rate in the chip formation zone as coupled with FO. Composite failure criteria combined with strain rate-dependent material strengths are used to determine chip failure onset. The model predicts and explains chip failure mode transitions and cutting force variation with FO and cutting speed. Second, the analytical framework is extended to MD CFRP by incorporating ply-constraining effects. The in-situ strengths of each constrained ply are derived by a fracture-mechanics approach to determine chip failure under the stress loadings from both cutting tool and fabrication-induced thermal residual stress, enabling cutting force prediction for MD laminates with different FO combinations. The identified ply-constraining effects explain the force variation in MD cutting. Third, a 3D micromechanical finite element framework is developed to simulate material removal and subsurface damage for different FOs. The results show that accounting for the pressure sensitivity of polymer matrix is necessary to capture the distinct removal mechanisms in cutting along and against fibers. Simulations with different cutting edge radii further explain the non-monotonic variation of surface roughness and subsurface damage. The proposed models advance the fundamental understanding of CFRP machining and support more predictive process planning, tool design, and damage control for high-value CFRP components.