Finite element investigation on pretreatment temperature-dependent orthogonal cutting of unidirectional CFRP

Mechanical properties and related machinability of carbon fiber reinforced polymer (CFRP) composites have a significant temperature dependence. In the present work, we elucidate the thermal-mechanical coupled material removal mechanisms of unidirectional CFRP composites with thermal and cryogenic pretreatments in orthogonal cutting by means of macro-scale finite element (FE) simulations. A thermal-mechanical FE model constituted with temperature-dependent constitutive law for CFRP as an equivalent homogeneous material is established. Furthermore, the failure behaviors of fiber reinforcement and polymer matrix is jointly characterized by Hashin and Puck fracture criteria, and a fracture energy-based damage propagation algorithm is proposed to account for the post-damage degradation behavior. The microscopic deformation mechanisms of 90°-oriented CFRP under orthogonal cutting, as well as their correlations with macroscopic cutting results in terms of cutting temperature evolution, machining force evolution, chip formation, subsurface damage and machined surface integrity, are firstly investigated by FE simulation and corresponding experiment performed at room temperature. Subsequent FE simulation results demonstrate significant temperature-dependent material characteristics of CFRP, i.e., cryogenic embrittlement and thermal softening, which have strong impacts on subsequent cutting processes. Furthermore, the coupling effect between fiber orientation and pretreatment temperature on the CFRP cutting is also addressed. Current findings provide guidelines for the rational design of temperature pretreatment strategy for enhancing machinability of CFRP composites.