Fatigue Life Calculator

Estimate fatigue life in cycles using the Basquin power-law relationship between stress amplitude and number of cycles.

MPa
MPa

Fatigue Life (N)

59,049 cycles

log10(N)4.77

Fatigue Life (N) vs Stress Amplitude (Sa)

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Formula

## 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).

Esempio Risolto

A steel component with Sf' = 900 MPa, b = -0.1, subjected to 300 MPa stress amplitude.

  1. 01Sa/Sf' = 300/900 = 0.3333
  2. 02N = (0.3333)^(1/(-0.1)) = (0.3333)^(-10)
  3. 03N = (1/0.3333)^10 = 3.0^10 = 59,049 cycles