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:

1. First step uses previous='Initial'
2. Subsequent steps chain from previous step name
3. 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:

• API Quick Reference
• Common Patterns
• Troubleshooting Guide