Abaqus Coupled Thermomechanical Analysis Workflow

Analyze problems where temperature and mechanical response interact. Use for thermal stress, expansion-induced deformation, and high-temperature structural components.

When to Use This Skill

Natural language triggers:

• "Thermal stress analysis"
• "Thermomechanical coupling"
• "Temperature causes stress/deformation"
• "Thermal expansion effects"
• "Heat causes deformation"
• "Thermal shock"
• "High temperature component"
• "Thermal gradient stress"

Route elsewhere:

• Heat transfer only (no stress) -> /abaqus-thermal-analysis
• Structural only (no thermal) -> /abaqus-static-analysis

Prerequisites

Before starting coupled analysis:

1. Working thermal OR structural analysis that converges
2. Material must have BOTH thermal and mechanical properties
3. Understand whether coupling is one-way or two-way

Workflow: Coupled Thermomechanical Analysis

Step 1: Determine Coupling Type

Ask if unclear: "Does mechanical deformation affect the temperature field?"

Scenario	Coupling Type	Approach
Heat causes stress, no feedback	One-way	Sequential coupling
Friction or plastic work generates heat	Two-way	Fully coupled
Large deformation changes heat path	Two-way	Fully coupled
Simple thermal expansion	One-way	Sequential is simpler

Decision rule: If only temperature affects stress -> Sequential. If deformation affects temperature -> Fully coupled.

Step 2: Define Complete Material Properties

Material must include BOTH sets:

Mechanical: E (Young's modulus), nu (Poisson's ratio)

Thermal: k (conductivity), alpha (expansion coefficient), T_ref (reference temperature)

For transient: Also need cp (specific heat) and rho (density)

Typical steel values (SI-mm units):

• E = 210000 MPa, nu = 0.3
• k = 50 mW/(mm*K), alpha = 12e-6 /K
• cp = 5.0e11 mJ/(tonne*K), rho = 7.85e-9 tonne/mm^3

Step 3: Choose Analysis Type

Fully Coupled (simultaneous):

• Use CoupledTempDisplacementStep
• Response: STEADY_STATE or TRANSIENT
• Elements: C3D8T, C3D8RT, or C3D10MT (coupled elements)

Sequential (thermal first, then structural):

1. Run thermal analysis with HeatTransferStep
2. Import temperature results into structural model
3. Run structural analysis with StaticStep

Step 4: Set Initial Conditions

• Define initial temperature (should match T_ref for zero initial stress)
• Thermal strain = alpha * (T - T_ref)

Step 5: Apply Boundary Conditions

Thermal BCs: Temperature, heat flux, convection, or radiation

Mechanical BCs: Fixed supports (prevent rigid body motion)

Step 6: Mesh with Appropriate Elements

Element	Description	Use
C3D8T	8-node coupled brick	General coupled
C3D8RT	Reduced integration	Faster, watch hourglassing
C3D10MT	10-node tet	Complex geometry

For sequential: Use standard thermal elements (DC3D8) then structural elements (C3D8R).

Step 7: Request Coupled Output Variables

Key variables to request:

• S: Mechanical stress
• U: Displacement
• NT: Temperature (nodal)
• THE: Thermal strain
• E: Total strain
• EE: Elastic strain (mechanical only)

What to Ask User

If requirements unclear, ask:

1. Is the coupling one-way (heat->stress) or two-way (mutual interaction)?
2. Steady-state or transient thermal conditions?
3. What is the reference temperature (zero thermal strain)?
4. What temperatures will be applied?
5. Are there any mechanical loads in addition to thermal effects?

Validation Checklist

After setup, verify:

• Expansion coefficient (alpha) defined with correct T_ref
• Initial temperature matches T_ref (for zero initial stress)
• Both mechanical and thermal BCs applied
• Using coupled elements (C3D*T) for fully coupled
• Thermal strain (THE) appears in output requests

Troubleshooting

Problem	Likely Cause	Solution
Large/unrealistic thermal strain	Wrong alpha units	alpha should be ~1e-5/K for metals
Zero thermal stress	Missing Expansion property	Add material.Expansion()
Non-convergence	Large temperature change	Reduce time increments or deltmx
No thermal expansion effect	Wrong element type	Use coupled elements (C3D8T not C3D8)
Cannot import ODB	Path or step name wrong	Verify ODB exists and step name matches

Related Skills

• /abaqus-thermal-analysis - Thermal-only (heat transfer without stress)
• /abaqus-static-analysis - Structural-only (no thermal effects)
• /abaqus-field - Import temperature fields from external sources
• /abaqus-material - Material property definitions
• /abaqus-step - Analysis step configuration

Code Patterns

For API syntax and code examples, see:

• API Quick Reference
• Common Patterns
• Troubleshooting Guide