Numerical simulation and experimental investigation on the residual stresses in a laser beam welded dual phase DP600 steel plate: Thermo-mechanical material plasticity model

Abstract

International audienceA thermo-mechanical plasticity material model, which consists of a hardening and a temperature sensitivity term, is built to describe the dual phase DP600 steel behavior. For the hardening term, a synthesis Ludwik–Voce hardening law is proposed, identified and compared with the classical Ludwik and the Voce hardening laws. For the temperature sensitivity function, a new proposed expression together with a classical Johnson–Cook term and an improved Chen term are analyzed and identified. Moreover, the plate anisotropy of DP600 is also taken into account using Hill-48 theory. Based on the plasticity material model, a numerical sequential coupled thermo-mechanical model is applied to investigate the residual stresses of laser welding process. It is shown that the material anisotropy and the thermo-mechanical elastic-plastic model have an important influence on numerical residual stresses results. An experiment is also carried out to verify the numerical model. Simulation results of residual stresses are in good accordance with neutrons diffraction measurements

Fatigue life prediction for butt‐welded joints considering weld‐induced residual stresses and initial damage, relaxation of residual stress, and elasto‐plastic fatigue damage

“…In the structural integrity evaluation, fatigue failure becomes one of the dominant concerns. Existing studies have revealed that there are mainly three factors impacting the fatigue property of welded joints: (a) the welding residual stresses, (b) local plastic deformation resulting from the welding process, and (c) the interaction between residual stresses and fatigue damage during cyclic loadings. Some approaches have been proposed to address one or two influencing factors .…”

“…Numerical simulation methods have the advantage of reconstructing the field of the entire structure through the actual welding progress. Finite element (FE) methods have become an effective approach in the approximate analysis of welding residual stresses . Lee et al proposed an FE evaluation to calculate the weld‐induced residual stresses and took into account a solid‐state phase transformation in carbon steel during the calculation.…”

“…Lee et al proposed an FE evaluation to calculate the weld‐induced residual stresses and took into account a solid‐state phase transformation in carbon steel during the calculation. Liu et al developed a thermo‐mechanical material plasticity model to obtain the weld‐induced residual stresses and validated the emulated results with experimental data. Khurshid et al applied a treatment of ultrasonic impact to three different kinds of steel, conducted both an experimental and a numerical study to evaluate the welding residual stresses, and then obtained consistent results.…”

“…cumulative plastic strain during the entire welding period; q f , q r , front and rear heat sources; Q V , thermal generation per unit volume; Q, heat source power; R, stress ratio; R ν , the triaxiality function; δS D , surface density of microcracks and intersections of microvoids; δS, area of cross section cutting the representative volume element (RVE); δS R , effective area of resistance, δS R = δS − δS D = δS(1 − D); S ij, min , S ij, max , minimum and maximum values of the ijth components of the deviatoric stress tensor; T, instant temperature; t, time; U, voltage of the welding process; v, welding velocity; z 0 , initial z-coordinate of the applied heat source; α, expansion coefficient of material; α ij , S ij , deviatoric part of back stress and stress; γ k , material parameters in kinematic hardening rule; δ ij , Kronecher delta; ε ij ; ε e ij ; ε p ij , total strain, elastic strain, and plastic strain; ε p ij : , evolution of plastic strain; η, welding arc efficiency; λ, heat conductivity of material; λ : , plastic multiplier; ν, Poisson's ratio of material; ρ, density of material; ∇, spatial gradient operator; σ e , effective stress; σ a , amplitude of fatigue loading; σ eq , von Mises equivalent stress; σ eqmax , maximum equivalent stress during the welding process; σ eq, max , maximum equivalent stress during fatigue loading; σ H , hydrostatic stress; σ H, m , mean hydrostatic stress; σ max , maximum cyclic stress; σ ij , Cauchy stress; σ l0 , fatigue limit of material; σ u , ultimate value of tensile stress; σ x , axial normal residual stresses in x-direction; σ y , axial normal residual stresses in y-direction; σ ′ y , yield stress the dominant concerns. Existing studies have revealed that there are mainly three factors impacting the fatigue property of welded joints [1][2][3][4][5][6] : (a) the welding residual stresses, (b) local plastic deformation resulting from the welding process, and (c) the interaction between residual stresses and fatigue damage during cyclic loadings. Some approaches have been proposed to address one or two influencing factors.…”

“…Some approaches have been proposed to address one or two influencing factors. [4][5][6] However, it is very difficult to completely consider all the three factors simultaneously. Residual stresses during the welding process significantly influence the fatigue behaviour of welded structures.…”