Thermomechanical problem

Project Support
1

Problem Description:

I am simulating a tool assembly (Extrusion Die and Head) made of dissimilar materials. The goal is to observe how differential thermal expansion causes the initial contact interface to separate (opening a gap), and how this separation affects the heat transfer between the two components.

Model Setup:

  • Physics: Coupled Thermomechanical (Static Structural + Heat Transfer).

  • Initial Condition: Components are in contact at t=0.

  • Loading: Internal pressure ramp and thermal loading to operating temperature.

  • Contact: Physical Contact with “Enable Heat Transfer” set to Yes.

Current Issues:

  1. Singularity & Stability: As soon as the components begin to separate due to thermal expansion, the “floating” component (the Die) loses its primary constraint, leading to rigid body motion errors and solver crashes (Parallel Process/Matrix Singular errors).

  2. Thermal Discontinuity: The solver struggles with the sudden drop in thermal conductance as the contact transitions from “Solid-to-Solid” to a “Gap” (Air/Vacuum).

  3. Hardware Constraints: The high mesh density required to resolve the contact interface (approx. 0.01m on a 40cm part) combined with 2nd-order elements is causing “Out of Memory” errors on standard computing nodes.

Steps Taken So Far:

  • Implemented Automatic Time Stepping to capture the non-linear contact transition.

  • Applied Load Ramping via tables for both pressure and temperature to improve convergence.

  • Added Surface Refinement on the contact faces.

  • Ensured no conflicting “Bonded” contacts exist on the same faces.

Seeking Advice On:

  1. Stabilization: Best practices for using Elastic Supports (artificial springs) to prevent rigid body motion without over-constraining the thermal expansion.

  2. Contact Stiffness: Recommendations for scaling contact stiffness (Penalty Factor) to ease convergence in metal-to-metal separation.

  3. Thermal Gap Conductance: How to realistically model the thermal transition when the gap opens to prevent numerical oscillation.

2

Hello,

Rigid body motion: Add very soft Elastic Supports/Weak Springs to the die (or enable solver weak springs if available). Set stiffness several orders of magnitude lower than the structural stiffness so they only stabilize the model after contact opens.
Contact stiffness: Start with Program Controlled or reduce the penalty/contact stiffness scaling (e.g., 0.1–1.0× default) to improve convergence during separation.
Thermal gap conductance: Use a thermal contact conductance that varies with gap distance/pressure rather than an abrupt on/off transition. Include gap conduction (air) and, if temperatures are high, consider radiation across the gap.
Memory issues: Use local mesh refinement only at the contact zone, switch to 1st-order elements where acceptable, and consider symmetry/submodeling to reduce DOF.