Study of plastic damage during Surface Mechanical Attrition Treatment for TWIP/TRIP steels using a dislocation density based viscoplasticity damage model
EUROMAT2019-European Congress and Exhibition on Advanced Materials and Processes, Stockholm, 1-5 September
Introduction/Purpose Surface Mechanical Attrition Treatment (SMAT) is a mechanical surface treatment process that generates higher level of compressive residual stress coupled with stronger plastic deformation in the near surface region of structures than conventional shot peening. SMAT is based on multidirectional mechanical impacts between balls and the surface of material. The particularity of this technique lies in the fact that it can transform the top surface layer of material from coarse grains to nano-sized grains due to severe plastic slips. The over-treatment during surface mechanical treatments such as shot peening can generate damage in the near surface region. A good understanding of deformation mechanisms of material during SMAT, including damage, is important in terms of material processing optimization. Methods In this work, the damage evolution during impact loading is numerically investigated. For this purpose, a dislocation density-based viscoplastic constitutive model coupled with damage is proposed. The mechanical behavior of twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) steels is described by a dislocation density-based viscoplastic model including the kinetics of twinning and phase transformation of martensite, which allows to investigate the strain hardening behavior the materials. To predict the damage evolution of these ductile steels, the Gurson–Tvergaard–Needleman (GTN) yield criterion is combined with the dislocation density-based constitutive model. Results A user-defined subroutine is developed to implement these models and to obtain predicitive results that are in good agreement with experimental observations. Conclusions 3D numerical simulations of single impacts are performed to investigate the impacting process as well as the damage evolution due to high strain rate impacts.