Fully coupled temperature-stress finite element analysis for thermal stresses in laser aided dmd process

Abstract

Despite enormous progress in Laser Aided Direct Metal/Material Deposition (DMD) process many issues concerning the adverse effects of process parameters on the stability of variety of properties have been reported. Delamination at substrate-deposition interface and cracking between deposited layers are some of these crucial issues that occur due to excessive stress build-up. Significantly high heating and cooling rates are inherent to DMD process, and consequently, the effects of solid state phase transformations on stress accumulation can not be neglected. This article is an attempt towards a comprehensive modeling of process parameters, temperature history, phase transformation kinetics, and the transient/residual thermal stresses in laser aided DMD process. Two different models have been proposed based on the metallo-thermo-mechanical theory. While the first model is based on sequentially coupled temperature-phase transformation-stress/strain fields, the second model is based on fully coupled temperature-stress/strain fields. Finite element solutions for these nonlinear process models substantiate the enormous disparity between the two models. In a study of two-pass single layer deposition of H13 tool steel on mild steel substrate, residual stress variations of up to 250 MPa between the two models have been observed. This article also reveals the significance of phase transformation effects. The same has been verified through the comparison of residual stresses with and without the inclusion of phase transformation kinetics.Despite enormous progress in Laser Aided Direct Metal/Material Deposition (DMD) process many issues concerning the adverse effects of process parameters on the stability of variety of properties have been reported. Delamination at substrate-deposition interface and cracking between deposited layers are some of these crucial issues that occur due to excessive stress build-up. Significantly high heating and cooling rates are inherent to DMD process, and consequently, the effects of solid state phase transformations on stress accumulation can not be neglected. This article is an attempt towards a comprehensive modeling of process parameters, temperature history, phase transformation kinetics, and the transient/residual thermal stresses in laser aided DMD process. Two different models have been proposed based on the metallo-thermo-mechanical theory. While the first model is based on sequentially coupled temperature-phase transformation-stress/strain fields, the second model is based on fully coupled temperatu...