Analytical model of CFRP cutting mechanics with strain rate effect

Abstract

When machining carbon fiber reinforced polymer (CFRP), the effect of strain rate on chip formation as fiber orientation and cutting speed change remains unclear, although it is recognized that the mechanical properties of CFRP are sensitive to strain rate. This paper provides a new analytical model to predict chip formation and associated cutting forces for CFRP. The changing cutting strain rate and stress states of varying fiber orientations are modeled, and the variation of CFRP strength due to strain rate is incorporated into selected composite failure criteria for determining material failure mode in cutting. Orthogonal cutting experiments were conducted on CFRP workpieces with distinct fiber orientations to validate the model. It is found that the model can capture the experimental cutting forces for CFRP workpieces with different fiber orientations across the full range [0°, 180°] at different cutting speeds. The simulations show that, due to the cutting strain rate, the strengths of CFRP in different loading directions can increase by up to 2.8 times compared to corresponding quasi-static strengths for varying fiber orientations at cutting speed 100 m/min. However, the sensitivity of cutting forces with the strain rate highly depends on the fiber orientation. As the fiber orientation varies, four distinct failure cases are classified based on the simulated different situations of strain rate-induced strength enhancement and stress-based failure modes. The simulated transitions of the failure cases explain the variations of experimental cutting forces. This work provides a new understanding of the CFRP cutting mechanism with strain rate effect.