Modeling multi-directional CFRP cutting mechanics with ply-constraining effect

During carbon fiber-reinforced polymer (CFRP) machining, the cutting forces of a multi-directional (MD) laminate can be significantly higher or lower than the superposed cutting forces from unidirectional (UD) laminates for different fiber orientation (FO) combinations, with the underlying mechanism remained unclear. This study proposes a new analytical cutting mechanics model for MD CFRP with ply-constraining effect. The constrained ply in-situ strengths in MD CFRP are derived by determining the onset of crack propagation by fracture mechanics. The cutting strain rate as well as stress for a constrained UD ply with changing FOs are modeled. Then, by strain rate-dependent physics-based failure criteria with in-situ strengths, the material failure of each ply during chip formation is determined. With the model, the failure stress and failure mode of each constrained UD ply with varying FOs are simulated, bringing forth the cutting force prediction for the whole MD laminate. The model-simulated cutting forces agree with experimental values for a series of MD CFRP workpieces with different FO combinations. Distinct ply-constraining effects within different FO ranges are identified and analyzed, which explain the different situations of the cutting force variation from UD laminates to MD laminates for the first time. The study contributes to a new understanding for chip formation and cutting force generation of MD laminates with various FO combinations. • A new cutting mechanics model for MD CFRP including ply-constraining effect. • More accurate prediction of MD CFRP cutting force variation than UD superposition. • Ply in-situ strengths from fracture mechanics are incorporated in MD CFRP cutting. • Ply constraint and strain rate jointly affect cutting stress and failure mode. • Constrained fiber deflection from UD CFRP to MD CFRP can reduce cutting force.