Dynamic behaviour and formation mechanism of shear band during high speed cutting Inconel 718

Abstract

Abastract In this paper, the shear zone storage energy model and strain gradient theory were compiled into a subroutine for secondary development to implement multi-scale finite element simulations. The shear zone storage energy was analyzed based on the variation of stress, temperature, and overall dislocation density. The plastic deformation behavior occurred in cutting was analyzed by combining microscopic and macroscopic based on the change of storage energy in the shear zone. The dynamic recrystallization and periodic fracture theories were also correlated with the variation of shear zone storage energy to investigate the mechanism of adiabatic shear zone formation in depth. It was found that the overall dislocation density, stress and shear zone storage energy change in the same trend, and the temperature and shear zone storage energy change in the opposite trend. The proliferation and annihilation of dislocations affect the change of storage energy. The storage energy reaches a peak of 9.6704 KJ when the overall dislocation density increases to a critical value of 7.7664×109, during which the stress gradually increases to 1.920×109Mpa. The local interaction between geometric dislocations and grain boundaries will contribute to the increase of stored dislocations due to local work hardening, which causes spontaneous deformation instability and thus the gradual formation of deformation zones. When the shear zone temperature reaches a peak of 886°C, the stress gradually decreases to 6.27×108Mpa. The aggravation of the stress concentration phenomenon caused the workpiece to release a large amount of heat energy because it could not bear the excessive strain, and the resulting thermal softening effect caused the hardness to decrease. At the same time, dislocations accumulate and new dislocation sources in the vicinity were activated, which caused the overall dislocation density to start decreasing and the material to undergo local shear instability, thus leading to dynamic recrystallization and the formation of a phase transition zone at high temperature. The storage energy decreases to a trough value of 3.1555 KJ when the overall dislocation density decreases to 2.5342×109. Dynamic recrystallization happens at different stages due to the change of storage energy, and the rate of storage energy change will affect the nucleation rate of dynamic recrystallization and thus the rate of adiabatic shear zone formation.