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: