Effect of Pressure-Dependent Yielding of Polymer Matrix on Material Removal Mechanisms in CFRP Machining

Since the polymer matrix in carbon fiber reinforced polymers (CFRPs) exhibits pressure-dependent yielding, its deformation and failure behaviors differ when machining CFRPs at different fiber orientations (FOs), due to the different stress states in cutting zone for each FO. However, existing micromechanical finite element (FE) models for machining CFRP modeled polymer with pressure-independent constitutive models, which can lead to inaccurate simulations of CFRP material removal. This paper investigates the effect of pressure-dependent yielding of polymer matrix on material removal mechanisms during CFRP machining. A modified Drucker-Prager (D-P) model for matrix is used in a micromechanical FE model of CFRP machining for the first time. The cutting forces, machined surface topography and chip morphology in simulations and experiments are compared for different FOs to validate the developed model. Results show that the pressure-dependent D-P model can capture both the matrix shear-deformation failure during cutting along fibers and the matrix brittle-cracking failure during cutting against fibers. Consequently, the model correctly simulates the sheet chip and smooth surface when cutting along fibers, and the block chip and saw-teeth surface when cutting against fibers. In comparison, the pressure-independent Mises model always predicts ductile shear-deformation failure for the matrix regardless of FO, and thus only captures the material removal when cutting along fibers. Compared to the Mises model, the D-P model improves cutting force prediction by 12.3% for cutting along fibers, and by 46.5% for cutting against fibers.