On the material removal processes and fibre deformation mechanisms in CFRP cutting based on a novel numerical model considering the strain rate effect

Carbon fibre reinforced plastics (CFRPs) are prone to various cutting-induced damages. An accurate model capable of effectively predicting the material removal and fibre deformation mechanisms would thus aid in reducing these damages and further enhancing machining quality. Previous research has proposed microscopic numerical models to predict the orthogonal cutting of unidirectional CFRPs with the local failure and fracture processes of the constituent phases. However, during the material modelling, the different failure modes of fibres under multi-directional loadings are often neglected, and the variation in resin mechanical properties with strain rate in cutting process is rarely considered. This would lead to inaccurate predictions of the cutting process and fibre deformation extent. To address this issue, this study has developed a novel microscopic numerical model to simulate the CFRP cutting with high precision. In the numerical model, the damage initiation criteria of fibre involve four distinct failure modes and the contributions from stresses in both the principal and shear directions, and the damage accumulation process in fibres is considered by defining evolution laws. Moreover, a constitutive model incorporating the strain rate effect is formulated to characterise the material behaviour of resin during cutting. Based on this numerical model, the machining processes and cutting forces of CFRPs at four typical fibre cutting angles are predicted. The simulation results agree well with the experimental observations, and the prediction accuracy has been improved compared with the numerical model using commonly applied material models of fibre and resin. Furthermore, the effects of processing conditions on fibre deformation are evaluated. The maximum fibre deformation depth is found when the fibre cutting angle is 90°. The fibre deformation depth decreases remarkably with the rise of cutting speed until 1000 mm/s. Additionally, the increased fibre deformation depths are predicted with the higher cutting depths.