Numerical Simulations Of Surface Mechanical Attrition Treatment On 316L Stainless Steel

Abstract

Surface mechanical attrition treatment (SMAT) is a flexible and cost-effective method for surface modification of metallic materials, such as 316L stainless steel. During SMAT, a sonotrode generates ultrasonic vibrations, propelling shot particles inside the enclosed chamber to impact the surface of the target. Due to the high vibration frequency, the target surface is impacted by the shot at high speed over a short treatment duration, causing the surface to undergo severe plastic deformation. How to control the process to achieve specific microstructure and material properties is yet to be fully understood. Modelling SMAT process is a complex but feasible way. Firstly, a DEM model was built to simulate the SMAT process with a rough-surface sonotrode and to investigate the effects of the different processing parameters on shot-target interactions. The effects of the sonotrode roughness on the distributions of impact angle and vertical velocity are carefully investigated. Thereafter, the effects of the processing parameters are also studied. Secondly, a sequential DEM-FEM modeling method was proposed for predicting the material properties after SMAT. The initial impact velocities and positions, determined by DEM simulations, were imposed as input in the FEM model. The multiple impact model considers the effects of treatment duration, shot number, velocity distribution, impact angle distribution and shot size on the roughness, PEEQ and residual stresses of the treated material. The third part of the thesis develops a three-dimensional crystal plasticity finite element (CPFE) model to simulate the grain refinement of 316L polycrystalline during SMAT, considering the evolution of the grain crystallographic orientations. The effects of the vertical impact velocities and shot sizes on the grain refinement are examined in detail.