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Hello Everyone,

I am working on a transient thermomechanical model for predicting the residual stresses. In the model a volumetric heat source (e.i, laser) heats the material time dependently. The model considers thermal expansion and nonlinear elastic-plastic material model (Plasticity) with linear isotropic hardening. In addition, the material phase change option (solid to liquid) is also added under the heat transfer physics. If I only include the thermal expansion and dont consider the plasticity and phase change, the model is solved fully coupled (time dependent) without any problem. But once the phase change and the plasticity are added, the model faces convergence problem in heat transfer and solid mechanics. By changing the solver setting for the heat transfer (phase change), selecting time steping as Generalized alpha and termination method as highly nonlinear Newton Raphson, the heat transfer converges (without considering the plasticity). Once the plasticity is added the model diverges completely and gives error of the form shown in screen shot and below.

Note: The solver solves the both physics segregately as suggested by the COMSOL automatically.

I would greatly appreciate any insights, suggestions, or recommendations from the community to help resolve this convergence problem and enable the successful integration of plasticity and phase change into the model.

Best regards, A. Reshad Bakhtari

Error: Repeated error test failures. May have reached a singularity. Time: 1.1958241991089191e-05 s. Solid Mechanics The computed plastic multiplier is negative. Geometry: geom1, Domain: 2 Failed to evaluate variable. Variable: comp1.solid.eiel11, Defined as: comp1.solid.epl11+comp1.solid.eth11 Failed to evaluate variable. Variable: comp1.solid.eel11, Defined as: comp1.solid.el11-comp1.solid.eiel11 Failed to evaluate variable. Variable: comp1.solid.sel11, Defined as: ((comp1.solid.D11comp1.solid.eel11)+(comp1.solid.D12comp1.solid.eel22))+(comp1.solid.D13comp1.solid.eel33) Failed to evaluate variable. Variable: comp1.solid.Sel11, Defined as: comp1.solid.sel11 Failed to evaluate variable. Variable: comp1.solid.Sl11, Defined as: comp1.solid.Sel11 Failed to evaluate expression. Expression: (-comp1.solid.Sl11)dvol Failed to evaluate Jacobian of expression. Expression: (-comp1.solid.Sl11test(comp1.solid.el11)-2comp1.solid.Sl12test(comp1.solid.el12)-2comp1.solid.Sl13test(comp1.solid.el13)-comp1.solid.Sl22test(comp1.solid.el22)-2comp1.solid.Sl23test(comp1.solid.el23)-comp1.solid.Sl33test(comp1.solid.el33))(dvol) The computed plastic multiplier is negative. Geometry: geom1, Domain: 2 Failed to evaluate variable. Variable: comp1.solid.eiel11, Defined as: comp1.solid.epl11+comp1.solid.eth11 Failed to evaluate variable. Variable: comp1.solid.eel11, Defined as: comp1.solid.el11-comp1.solid.eiel11 Failed to evaluate variable. Variable: comp1.solid.sel11, Defined as: ((comp1.solid.D11comp1.solid.eel11)+(comp1.solid.D12comp1.solid.eel22))+(comp1.solid.D13comp1.solid.eel33) Failed to evaluate variable. Variable: comp1.solid.Sel11, Defined as: comp1.solid.sel11 Failed to evaluate variable. Variable: comp1.solid.Sl11, Defined as: comp1.solid.Sel11 Failed to evaluate expression. Expression: (-comp1.solid.Sl11)dvol Failed to evaluate Jacobian of expression. Expression: (-comp1.solid.Sl11test(comp1.solid.el11)-2comp1.solid.Sl12test(comp1.solid.el12)-2comp1.solid.Sl13test(comp1.solid.el13)-comp1.solid.Sl22test(comp1.solid.el22)-2comp1.solid.Sl23test(comp1.solid.el23)-comp1.solid.Sl33test(comp1.solid.el33))(dvol) Last time step is not converged.