Fatigue Life Calculator
Estimate fatigue life in cycles using the Basquin power-law relationship between stress amplitude and number of cycles.
Fatigue Life (N)
59,049 cycles
Fatigue Life (N) vs Stress Amplitude (Sa)
Formule
## Basquin's Law for Fatigue Life Fatigue failure occurs when a material is subjected to repeated cyclic loading below its static strength. Basquin's equation relates stress amplitude to the number of cycles to failure. ### Formula **Sa = Sf' × (2N)^b** or equivalently **N = (Sa / Sf')^(1/b) / 2** Sf' is the fatigue strength coefficient (approximately the true fracture strength), b is the fatigue exponent (typically -0.05 to -0.15 for metals), and N is the number of reversals to failure (2N = cycles).
Exemple Résolu
A steel component with Sf' = 900 MPa, b = -0.1, subjected to 300 MPa stress amplitude.
- 01Sa/Sf' = 300/900 = 0.3333
- 02N = (0.3333)^(1/(-0.1)) = (0.3333)^(-10)
- 03N = (1/0.3333)^10 = 3.0^10 = 59,049 cycles
Questions Fréquentes
What is the endurance limit?
Some materials (notably steels) exhibit an endurance limit: a stress below which fatigue failure theoretically never occurs. For steels, it is roughly 40-50% of UTS. Aluminum and most non-ferrous metals do not have a true endurance limit.
How does mean stress affect fatigue?
A tensile mean stress reduces fatigue life compared to fully reversed loading. Corrections like the Goodman, Gerber, or Soderberg diagrams adjust the allowable stress amplitude based on mean stress.
What factors reduce fatigue life?
Surface roughness, stress concentrations (notches, holes), corrosive environment, elevated temperature, and residual tensile stresses all reduce fatigue life. Shot peening and polishing can improve it.
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