Fatigue Life (S-N, Basquin & Goodman)

Estimate the cycles to failure from the stress amplitude using the Basquin S-N relation with a Goodman mean-stress correction, free online.

Stress amplitude σa (MPa)

Mean stress σm (MPa)

Ultimate tensile strength Su (MPa)

Fatigue strength coefficient σ'f (MPa)

Fatigue strength exponent b

About this calculator

Basquin: σ_a = σ′_f·(2N_f)^b, so N_f = ½(σ_a ÷ σ′_f)^(1/b). A mean stress is accounted for with the Goodman line: σ_ar = σ_a ÷ (1 − σ_m ÷ S_u). Typical steel values: σ′_f ≈ 1.5 × S_u, b ≈ −0.09. For quick estimates only; use test data for critical parts.