The Macro And Micro Simulation Of Cutting Carbon Fiber Reinforced Plastic Composites

Carbon Fiber Reinforced Plastic Composites (CFRP) is a kind of advanced composite materials. It has excellent mechanical properties, and is widely used in many fields. But due to the particularity of CFRP on the structure, it is a mixed state of fiber and resin on microscopic, and has an anisotropic characteristic on macroscopic. It is prone to appear different sorts of damage, such as delamination, burr and tear. Different from the traditional metal cutting, the cutting of CFRP doesn't has an obvious cutting zone, it is a process of interaction of tool with fiber and resin which makes it complicated to reveal the removal mechanism of CFRP. The removal mechanism of CFRP should be further understood to avoid the occurrence of damage and improve the machining quality. Experiment, theory and numerical simulation are the three important means to solve the problem of cutting CFRP. The finite element simulation method is used in the cutting area more and more. In this paper, the simulation method and experimental method are both used to reveal the removal mechanism of cutting CFRP. As CFRP is not a kind of isotropic material, which is made up of fiber, resin and interface at the microscopic level, and has characteristics of across scales and anisotropic, the removal mechanism of CFRP should be discussed from micro and macro scales to reveal the process of local failure at microscopic level and chips formation at macro level.To reveal the local fracture of CFRP at micro level, a micro model is established including fiber phase, resin phase and interface phase and each phase considers their respective material constitutive model, initial failure criterion and damage evolution theory. Structurally, the micro model is based on multiphase, fiber phase, resin phase and interface phase. The part with participating cutting is refined to improve the computational efficiency. On the material properties, different phase follows their respective material constitutive, initial damage and damage evolution rules. Fiber phase adopt linear elastic constitutive model and uses Hashin failure criterion. Resin phase adopt elastic-plastic constitutive model and use shear failure criterion. The interface phase uses cohesive element to simulate the behavior of interface. On this basis, four typical fiber orientations micro models are established to simulate the local failure process of fiber/matrix fracture, interface crack.To analyze the influence of different cutting parameters on chip formation and cutting force, a macro model based on equivalent homogeneous method is established. The VUMAT subroutine in ABAQUS is used to define the CFRP material properties involving 3D linear elastic constitutive,3D Hashin failure criterion, and damage evolution rule. The macro model is used to simulate the formation of continuous chips, and the change rules of cutting force with different cutting parameters and fiber orientations. The residual stiffness is also considered to introduce the maximum stiffness degradation coefficient. In addition, the friction coefficient changes with the fiber orientation, so Coulomb friction is used. On this basis, the 3D macro cutting model is established to simulate the macro cutting process of CFRP.A macroscopic model based on the EHM method and a multiphase microscopic model consisting of a fiber phase, a matrix phase, an interface phase and an equivalent homogeneous phase are both established to analyze the material removal mechanism from the local failure to the macro chip formation. A microscopic observation experiment is also designed to verify the reliability of models. The cutting mechanism is different under different fiber orientations. For example, the forms of destruction that occur at a fiber orientation of 0° are primarily interface cracking and fiber bending; the resulting chips have long shapes. The cutting force and depth of sub-surface damage are both relatively small. The micro model is used to simulate the local failure process of fiber/matrix fracture, interface crack and the macro model is used to obtain continuous chip formation and the change rule of cutting force with different cutting parameters and fiber orientations. The sub-surface damage is also forecasted. All these provide a conference to optimize cutting parameters and tool angles.