abaqus-fatigue-analysis

# 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: 1. Run structural analysis in Abaqus (stress/strain results) 2. Extract stress history from ODB 3. Apply fatigue criteria externally (Basquin, Miner's rule) For full fatigue analysis, consider external tools: **fe-safe**, **nCode**, **FEMFAT**. ## Prerequisites Before fatigue analysis: 1. ✅ Completed static or dynamic analysis with converged results 2. ✅ Material fatigue data (S-N curve or Coffin-Manson parameters) 3. ✅ 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 components - `PEEQ` - Equivalent plastic strain (for low-cycle) ### Step 2: Identify Critical Location Find the maximum stress location: - Use `/abaqus-odb` to 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](references/api-quick-ref.md) - [Common Patterns](references/common-patterns.md) - [Troubleshooting Guide](references/troubleshooting.md)