Fatigue Test Standards
Engineering context for the standards that govern fatigue testing — S-N curves, strain-life, crack growth and how the data feeds structural fatigue analysis.
What is it?
Fatigue test standards define how material specimens are cyclically loaded to generate S-N curves, strain-life data or crack growth data. ASTM E466 covers force-controlled axial fatigue testing of metals. ASTM E606 covers strain-controlled low-cycle fatigue. ASTM E647 covers crack growth rate measurement. ISO 1099 and ISO 12106 are the ISO equivalents.
What each test provides
| Test type | Standard | Data produced |
|---|---|---|
| High-cycle fatigue (S-N) | ASTM E466 / ISO 1099 | Stress vs cycles to failure — for long-life fatigue assessment |
| Low-cycle fatigue (strain-life) | ASTM E606 / ISO 12106 | Strain amplitude vs reversals — for plastic fatigue |
| Crack growth (da/dN) | ASTM E647 | Crack growth rate vs stress intensity range — for damage tolerance |
| Fracture toughness | ASTM E399 / E1820 | K_Ic or J_Ic — for critical crack size assessment |
Why it matters to engineering analysis
Fatigue test data provides the S-N curves and crack growth laws used in structural fatigue and damage tolerance assessment. The engineer must use data from the correct material, temper, orientation and environment. MMPDS and CMH-17 compile statistically-based fatigue data for aerospace materials.
Specimen considerations
- Surface finish: machined, ground or polished — affects fatigue life significantly
- Notch: Kt specimens give notched fatigue data for stress concentration effects
- Mean stress: R-ratio affects S-N curve position — test at the relevant R-ratio
- Environment: temperature, humidity and corrosive environments affect fatigue life