Weld Fatigue Life Calculator
Estimate fatigue life based on AWS D1.1/AISC fatigue categories and S-N curves.
AWS D1.1 Fatigue Categories
| Category | Cf (x10^8) | FTH (ksi) | FTH (MPa) |
|---|---|---|---|
| A | 250 | 24 | 165 |
| B | 120 | 16 | 110 |
| B' | 61 | 12 | 83 |
| C | 44 | 10 | 69 |
| C' | 44 | 12 | 83 |
| D | 22 | 7 | 48 |
| E | 11 | 4.5 | 31 |
| E' | 3.9 | 2.6 | 18 |
| F | 150 | 8 | 55 |
Weld Fatigue Design Principles
S-N Curve Equation
N = Cf / Sr^3 where N = cycles to failure, Cf = fatigue constant, Sr = stress range
Key Concepts
- Stress Range: Sr = Smax - Smin (the driving factor for fatigue damage)
- Stress Ratio: R = Smin/Smax (affects fatigue life but AWS uses Sr only)
- Threshold (FTH): Below this stress range, infinite life assumed
- Detail Category: Based on geometric stress concentration at weld
Common Detail Categories
- Category B: CJP groove welds ground flush, built-up members
- Category C: Transverse fillet welds, CJP T-joints
- Category D: Longitudinal fillet welds, cover plate ends (welded)
- Category E: Base metal at cover plate terminations
Improving Fatigue Life
- Reduce stress range by increasing weld/member size
- Improve detail category (CJP instead of PJP, grinding, etc.)
- Post-weld treatments: grinding, peening, TIG dressing
- Reduce stress concentrations at weld toes