diegosouzapw Abaqus Fatigue Analysis Skill
Predict fatigue life from FEA stress results using S-N curves and damage accumulation.
When to Use This Skill
Route here when user mentions:
- "fatigue", "how many cycles", "fatigue life"
- "durability", "S-N curve", "cycles to failure"
- "rainflow counting", "Miner's rule"
- "high-cycle fatigue", "low-cycle fatigue"
Route elsewhere:
- Just stress analysis →
/abaqus-static-analysis - Crack propagation → specialized fracture tools
- Static strength check →
/abaqus-static-analysis
Important: Abaqus Fatigue Limitations
Abaqus has limited native fatigue capabilities. The typical workflow is:
- Run structural analysis in Abaqus (stress/strain results)
- Extract stress history from ODB
- Apply fatigue criteria externally (Basquin, Miner's rule)
For full fatigue analysis, consider external tools: fe-safe, nCode, FEMFAT.
Prerequisites
Before fatigue analysis:
- ✅ Completed static or dynamic analysis with converged results
- ✅ Material fatigue data (S-N curve or Coffin-Manson parameters)
- ✅ Stress output at critical locations
Workflow Steps
Step 1: Run Stress Analysis
Use /abaqus-static-analysis for constant loads or /abaqus-dynamic-analysis for time-varying.
Ensure output requests include:
S- Stress components (principal, Mises)E- Strain componentsPEEQ- Equivalent plastic strain (for low-cycle)
Step 2: Identify Critical Location
Find the maximum stress location:
- Use
/abaqus-odbto extract peak stress - Check stress concentrations (fillets, holes, notches)
- Consider fatigue notch factor (Kf) vs stress concentration (Kt)
Step 3: Extract Stress History
For constant amplitude: single max/min stress values. For variable amplitude: full stress-time history for rainflow counting.
Step 4: Apply Fatigue Criteria
Use appropriate method based on loading and life regime.
Step 5: Calculate Life and Damage
Apply Basquin equation for life, Miner's rule for cumulative damage.
Key Decisions
Fatigue Approach
| Approach | When to Use | Data Needed |
|---|---|---|
| Stress-life (S-N) | High-cycle (N > 10^4) | S-N curve |
| Strain-life (e-N) | Low-cycle (N < 10^4) | Coffin-Manson params |
| Fracture mechanics | Crack growth | da/dN curve |
Loading Type
| Loading | Analysis Method |
|---|---|
| Constant amplitude | Single static analysis |
| Variable amplitude | Multiple loads + rainflow |
| Proportional | Single load case |
| Non-proportional | Critical plane method |
Mean Stress Correction
| Method | Use Case |
|---|---|
| Goodman | Conservative, tensile mean |
| Gerber | Less conservative |
| Soderberg | Very conservative |
| SWT | Strain-life with mean stress |
What to Ask the User
If unclear, ask:
- Material fatigue properties? S-N curve coefficients or test data?
- Loading type? Constant amplitude or variable (spectrum)?
- Mean stress? Fully reversed (R=-1) or with mean stress (R=0)?
- Critical location known? Or need to find max stress?
- Life target? What's the required number of cycles?
Key Parameters
| Parameter | Typical Values | Notes |
|---|---|---|
| S-N slope (b) | 0.08-0.15 | Lower = longer life |
| Endurance limit | 40-50% UTS (steel) | Stress below which infinite life |
| Fatigue notch factor (Kf) | 1.0-3.0 | Kf = 1 + q(Kt-1) |
| Notch sensitivity (q) | 0.7-0.95 | Higher for stronger steels |
Troubleshooting
| Problem | Cause | Solution |
|---|---|---|
| Unrealistically short life | Stress singularity | Use Kf correction, refine mesh away from singularity |
| Wrong units | MPa vs Pa mismatch | Verify stress units match S-N data |
| Unconservative prediction | Missing mean stress | Apply Goodman/Gerber correction |
| Very long calculated life | Stress below endurance limit | Check if stress > endurance limit |
Related Skills
/abaqus-static-analysis- Base stress analysis/abaqus-dynamic-analysis- Time-varying loading/abaqus-amplitude- Cyclic loading definition/abaqus-odb- Extract stress history from results
Code Patterns
For API syntax, equations, and code examples, see:
- API Quick Reference
- Common Patterns
- Troubleshooting Guide