A dislocation density-based multiscale cutting model for ultra-precision machining of AISI 4140 steel

Microstructural characteristics of a machined surface are significantly associated with its mechanical properties and deformation responses under cutting conditions. In this work, a dislocation density-based multiscale simulation model was proposed to simulate the material deformation behaviors in ultra-precision cutting of AISI 4140 steel. The model was built by coupling a three-dimensional discrete dislocation dynamic (3D-DDD) model with a finite element method (FEM) through the optimization of a dislocation densitybased (DDB) constitutive equation (compiled as a user-defined subroutine). The movement of edge and screw dislocations, such as generation, propagation, siding, and their interactions, was performed by 3D-DDD, and the statistical features of dislocations were used to optimize the critical constants of the DDB constitutive equation. A cutting model was then built to predict material deformation behaviors under various cutting conditions (cutting speed, feedrate, depth of cut). The simulation results indicate that the developed model can well capture the microstructure characteristics such as grain size and dislocation density distributions under the tested cutting conditions. The influence of feedrate and cutting speed on the distribution of dislocation densities and grain size was analyzed.