Cutting deformation mechanism of SiCp/Al composites based on strain gradient theory

Abstract

More and more experiments have shown that particle-reinforced metal matrix composites (PMMC) exhibit obvious size effects. The aclassic plasticity theory does not contain internal length scale and cannot explain this size effect. In this paper, based on the Taylor relationship, the concept of "geometrically necessary dislocations" and the mechanism of dislocation multiplication, slippage and extinguishing, a constitutive equation for SiCp/Al composites related to strain gradient is established. The established equation is imported into Abaqus for simulation by writing a user subroutine Vumat. Combining the simulation and experimental results, the effects of stress, temperature, cutting force, strain gradient effect and its dimensional effect on cutting deformation during machining SiCp/Al composites are analyzed from the perspectives of material micro-plasticity mechanics and material dislocation theory. The results show that the presence of SiC particles changes the microstructure of the matrix material, and induce a high strain gradient in the matrix. This high strain gradient makes the material more prone to shear deformation localization. In the cutting process, the defects and breakage of the SiC particles themselves will lead to the formation of micro-cracks. The growth of micro-cracks in the shearing area is an important factor in the generation of chips. By comparing the simulation results with the experimental results, the modified constitutive model is closer to the experimental results, indicating that the established theoretical model based on the strain gradient can better reflect the cutting process of particle-reinforced metal matrix composites.