Abaqus Step Skill
This skill defines analysis steps and procedures in Abaqus. Steps control what physics are solved and how the solution proceeds.
When to Use This Skill
Route here when user mentions:
- "static analysis", "dynamic step", "frequency analysis"
- "heat transfer step", "thermal step", "transient analysis"
- "analysis type", "time increments", "nlgeom"
- "convergence issues", "increment size", "time step"
- "multi-step analysis", "sequential loading"
- "buckling analysis", "modal analysis"
- "impact simulation", "crash analysis"
Route elsewhere:
- Applying boundary conditions →
/abaqus-bc - Applying loads →
/abaqus-load - Setting up optimization →
/abaqus-optimization - Configuring output requests →
/abaqus-output
Workflow: Creating Analysis Steps
Step 1: Understand User's Physics
Ask if unclear:
- What physics? Stress, vibration, heat transfer, coupled?
- Static or dynamic? Constant load vs time-varying?
- Linear or nonlinear? Small or large deformations?
Step 2: Choose Step Type
| Analysis Goal | Step Type | Key Parameter |
|---|---|---|
| Stress under constant load | StaticStep | nlgeom=OFF/ON |
| Natural frequencies | FrequencyStep | numEigen |
| Buckling modes | BuckleStep | numEigen |
| Transient dynamics (smooth) | ImplicitDynamicsStep | timePeriod |
| Impact/crash | ExplicitDynamicsStep | timePeriod |
| Heat conduction | HeatTransferStep | response |
| Thermal + structural | CoupledTempDisplacementStep | timePeriod |
| Harmonic response | SteadyStateDynamicsStep | frequencyRange |
Most common: StaticStep with nlgeom=OFF for linear stress analysis.
Step 3: Determine Linearity
| Condition | nlgeom Setting | When |
|---|---|---|
| Small deformation, linear material | OFF | Default, fastest |
| Large rotation/displacement | ON | Thin structures, cables |
| Plasticity | ON | Material yields |
| Contact | ON | Parts touching |
| Buckling | ON | Post-buckling behavior |
Step 4: Configure Increment Control
| Convergence Difficulty | initialInc | minInc | maxInc |
|---|---|---|---|
| Easy (linear) | 1.0 | 1e-6 | 1.0 |
| Moderate | 0.1 | 1e-8 | 0.2 |
| Difficult (contact, plasticity) | 0.01 | 1e-12 | 0.05 |
Step 5: Chain Multiple Steps (if needed)
For sequential loading:
- First step uses
previous='Initial' - Subsequent steps chain from previous step name
- Each step can have different physics or settings
Key Parameters
| Parameter | Purpose | Typical Value |
|---|---|---|
| timePeriod | Duration of step | 1.0 for static |
| initialInc | Starting increment size | 0.1 for nonlinear |
| maxNumInc | Maximum iterations | 100 |
| minInc | Smallest allowed increment | 1e-8 |
| maxInc | Largest allowed increment | 0.1-1.0 |
| numEigen | Modes to extract | 10 |
| deltmx | Max temp change per increment | 5.0-10.0 |
Special Considerations
Frequency/Modal Analysis
- Always from Initial step (no preload needed for basic modal)
- Use LANCZOS eigensolver for large models
- Extract 10-20 modes typically
Buckling Analysis
- Usually follows a load step (to apply reference load)
- Eigenvalues are load multipliers
- First positive eigenvalue is critical
Explicit Dynamics
- Time period should be very short (milliseconds)
- Increment size determined automatically
- Mass scaling may be needed for quasi-static problems
Heat Transfer
- STEADY_STATE for equilibrium temperature
- TRANSIENT for time-varying temperature
- deltmx controls accuracy vs speed
Troubleshooting
| Problem | Likely Cause | Solution |
|---|---|---|
| "Too many increments" | Convergence difficulty | Reduce maxInc, increase maxNumInc |
| "Negative eigenvalues" | Unconstrained or unstable | Check BCs, add stabilization |
| "Time increment too small" | Severe nonlinearity | Add stabilization, check material |
| "Explicit time increment" | Very small elements | Use mass scaling or coarsen mesh |
Validation Checklist
After step creation, verify:
- Step type matches analysis physics
- nlgeom setting appropriate for deformation level
- Increment control parameters reasonable
- Step chains correctly from previous
- Time period appropriate for transient analysis
Code Patterns
For actual API syntax and code examples, see:
