Formation of gradient residual stress in ultrasonic vibration-assisted end grinding inconel 718: microscopic mechanism and modeling

Abstract Residual stress (RS) on machined surfaces critically influences in-service performance. However, the underlying microscopic physical mechanisms remain insufficiently understood. The plastic deformation behavior under different parameters in ultrasonic vibration-assisted end grinding (UVAEG) was systematically investigated by RS characterization, in-situ grinding force measurement, and subsurface microstructure observation. An evaluation method for RS on machined surfaces was proposed. A prediction model for RS on machined surfaces was established based on dislocation pile-up theory. The microscopic mechanism of RS formation was analyzed. The effects of spindle speed and grinding depth on plastic deformation depth and the formation of gradient RS were also systematically studied. The results show that surface RS is positively correlated with dislocation density. The residual stress induced by grinding primarily originates from local stress fields generated by microstructural defects within the material. A larger plastic deformation depth is favorable for the formation of a deeper RS affected layer. Lower spindle speed and larger cutting depth can generate higher grinding forces, thereby promoting dislocation multiplication and migration, increasing the degree of lattice distortion and the depth of the affected layer, and consequently resulting in higher residual stress and a deeper affected layer. This study elucidates the microscopic mechanisms underlying internal stress formation at machined surfaces and provides a theoretical basis for optimizing machining processes to control material performance effectively.