Fatigue life of welded structures

S-N curve slope and fatigue life for a welded structure, from the fatigue strength parameter and applied stress amplitude (Eurocode 3 / NEN 2063 weld-detail categories).

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Fatigue strength parameter, KMPaAmplitude, fully reversed stressMPa

Slope of S-N curve, m3

Fatigue life, N_i0.9112500000000001 10⁶ cycles

Below the endurance limit (Sᵢ<0.55·Sk), life is infinite — shown as an unbounded fatigue life rather than a finite cycle count.

Method & references

Weld details per Eurocode 3, NEN 2063.
Low-cycle fatigue: Sᵢ>Sk, m=3, Nᵢ<10⁷. High-cycle fatigue: Sᵢ<Sk, m=5, 10⁷<Nᵢ<2×10⁸. Endurance limit: Sᵢ<0.55·Sk, Nᵢ>2×10⁸ (infinite life).

The computation is a literal port of the original client-side JavaScript from /engineering-abc/calculators/c3_6.htm. Results are verified equal to the original by an automated golden-master test. No formula has been re-derived or “improved”.

Fatigue life of welded structures — Engineering ABC