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Fatigue — Wöhler S-N curve

Basquin S-N curve fit · σ_a = σ_f'·(2N_f)^b

The fundamental fatigue lifetime curve. Pick a material preset, or paste your own (N, σ) test data and auto-fit. Reports operating-cycle life and high-cycle / infinite-life verdict.

Inputs

MPa
MPa
Typically ≈ Sut + 345 for steels (Roessle-Fatemi 2000)
—
Steels: −0.06 to −0.12 · aluminum: ~ −0.10 · Ni-base: ~ −0.09
MPa
Steel ≈ 0.5·Sut · Al + Cu have no real limit
cycles
MPa
Operating alternating stress amplitude (after Goodman if mean stress ≠ 0)
Optional: paste test data to auto-fit
PV plate; ASME VIII Div 2 Annex 5.B baseline

Results

Wöhler / S-N curve · Basquin σ_a = σ_f'·(2N)^b
endurance Se = 240Sut = 485N_op ≈ 3.6e+8 cycles10²10³10⁴10⁵10⁶10⁷10⁸10⁹1003001000cycles to failure N_f (log scale)stress amplitude σ_a (MPa, log)Basquin / Wöhler · ASME VIII Div 2 Annex 5.B · steels show endurance limit at N_e≈10⁶; non-ferrous decay continues
σ_f' = 850 MPa · b = -0.085 · Sut = 485 · Se = 240 @ N_e = 1e+6 · σ_a_op = 150 → N_op ≈ 3.6e+8 (INFINITE-LIFE)
Cycles to failure N_op (Basquin)3.64e+8cycles
VerdictINFINITE-LIFE
Stress at endurance Se240MPa
Margin to Se-37.5%
The Basquin curve assumes fully-reversed loading (R = −1). For mean-stress correction use Goodman / Soderberg / Gerber at /console/fatigue. For variable-amplitude spectra apply Miner's rule of cumulative damage.
Download all inputs + calculations + outputs as a single PDF.