Spring Fatigue Life Calculator

Inputs

Wire diameter (d)

Mean coil diameter (D)

Maximum force (Fmax)

Minimum force (Fmin)

Wire material

Shot peening

Default result

Fatigue factor of safety (n_f)

1.31

Pass

Above the 1.2 screening target on the Goodman line for infinite life.

Torsional Goodman: n_f = 1/(τa/Sse + τm/Ssu). Target ≥ 1.2 for screening.

Also computed

Alternating shear stress (τa) 180.9 MPa

Mean shear stress (τm) 301.5 MPa

Endurance intercept (Sse) 336.1 MPa

Goodman intercept from the Zimmerli point: Sse = Ssa/(1 − Ssm/Ssu).

Torsional ultimate (Ssu) 1,340 MPa

Ssu = 0.67·Sut.

Wire tensile strength (Sut) 2,000 MPa

Size-corrected minimum tensile strength from the material table.

Static factor at Fmax (n_s) 1.87

Allowable static torsional fraction of Sut at Fmax (material-table value).

Method notes 3 notes

Method: Shigley-style torsional Goodman screen using the Zimmerli infinite-life data, which is effectively independent of wire size and steel grade (unpeened Ssa = 241 MPa at Ssm = 379 MPa; peened 398 at 534). Ssu taken as 0.67·Sut with Sut = A/d^m from the cited material table.
The Wahl factor is applied to both stress components (conservative). Set-removed or pre-stressed springs and supplier S-N data can justify higher allowables.
Assumes the spring never goes slack or to coil bind in the cycle, room temperature, non-corrosive environment and no surge resonance — check natural frequency separately for high-speed cycles.