Free 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)
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).
Example Calculation
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
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