A comparison of cutting mechanisms of the carbon fibre reinforced thermoset and thermoplastic composites by the experimental and computational modelling methods

The unexpected damages are usually introduced during the machining of carbon fibre reinforced composites. There have been experimental investigations on the damage extent for machining thermoset and thermoplastic composites, and numerical simulations developed for the cutting characteristics of thermoset composites. However, studies on the material removal and chip formation mechanisms during the cutting of carbon fibre reinforced thermoplastics (CFRTPs), are rarely reported, which will significantly contribute to the machining quality improvement of CFRTPs. To this issue, numerical simulations and experiments were conducted in this paper to analyse the cutting mechanisms of CFRTPs, and to compare their cutting processes with the carbon/epoxy composites for guidance on damage suppression. In the developed finite element (FE) models, the carbon/epoxy composites were defined to be anisotropic with an elastic constitutive model, while an elastic-plastic damage model was proposed for CFRTPs. Specifically, a plastic yield function consisting of three-dimensional (3D) stress components was utilized to characterise the plasticity of CFRTPs under complex cutting loads. For these two materials, the initiation and evolution of the damage with different failure modes were determined based on the Hashin and Puck criteria and the strain energy density. With these FE models, the orthogonal cutting processes and forces of the composites under four fibre orientations were predicted, and the results agree well with the experimental outputs. It was found that the material removal mechanisms of CFRTPs with the four fibre orientations are diverse from the ones made from thermoset resins in terms of crack propagation, material fracture position and chip formation. Additionally, the shorter cracks and longer chips are usually produced when cutting CFRTPs with 0° and 45° fibre orientations compared with those of the carbon/epoxy composites with same layups. Moreover, the cutting forces of CFRTPs are higher than the carbon/epoxy composites at 0°, 45° and 135° fibre orientations.