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Compression Spring Fatigue Calculator

Use this calculator to estimate fatigue safety for a helical compression spring under cyclic loading. It reports Gerber, Goodman, and Sines fatigue factors of safety using spring geometry, cyclic loads, material strength, and shot-peening condition.

This page is intended for both general users and engineers. First size the spring with the main compression spring calculator, then use this page to check whether the selected geometry has enough margin under fluctuating loads.

Sinusoidal fluctuating loading for compression spring fatigue analysis

Cyclic loading is defined by minimum and maximum spring force.

Before you use this fatigue calculator

  1. Choose or design the spring geometry first.
  2. Check natural frequency if the spring runs at high cyclic speed.
  3. Enter the cyclic load range and material strength here.
  4. Compare the fatigue safety factors with your required design factor.

Important limit: the Zimmerli constants used here are intended for spring steels with wire diameter below 10 mm (about 3/8 in).

Inputs

Spring wire diameter.
Use the minimum force during the cycle, not zero unless the spring really unloads to zero.
Enter the required fatigue design factor. Typical values are greater than 1.
Only used when material is set to user defined.
This calculator checks for infinite-life style endurance margin using Zimmerli-based constants. It is most appropriate for small spring wire sizes under repeated loading.

Results

Design notes

    Equations used

    C = D / d Kw = (4C - 1) / (4C - 4) + 0.615 / C Fa = (Fmax - Fmin) / 2 Fm = (Fmax + Fmin) / 2 τa = Kw · 8 · Fa · D / (π · d³) τm = Kw · 8 · Fm · D / (π · d³) Ssu = 0.67 · Sut Shot peened Zimmerli constants: Ssa = 398 MPa, Ssm = 534 MPa Unpeened Zimmerli constants: Ssa = 241 MPa, Ssm = 379 MPa Sse,Gerber = Ssa / (1 - (Ssm / Ssu)²) Sse,Goodman = Ssa / (1 - (Ssm / Ssu)) Ssa,lim,Goodman = 1 / (1 / Sse + 1 / (r · Ssu)) Ssa,lim,Sines = Ssa

    Definitions

    Fatigue failure: damage caused by repeated loading cycles. Cracks begin at small defects and grow with time until failure occurs.

    Spring index: the ratio of mean coil diameter to wire diameter.

    Wahl factor: a curvature correction used to estimate spring-body shear stress more realistically.

    Design factor: the minimum safety margin required by your design standard or company practice.

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