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Fatigue is an issue in springs subjected to cyclic loading, where the force on the spring varies between a maximum and minimum value. For example, the springs in a car's shock absorption system would be subject to fatigue loading. Over time, excessive cyclic stresses from fatigue can cause the spring to fail.

Use this calculator to predict if a known spring subjected to a known range of loading forces will be in danger of failing from fatigue. The calculator outputs a GO / NO-GO assessment after checking the maximum shear stresses in the spring against Soderberg's criterion.

Inputs
  Spring free length, Lfree:    
  Spring constant, k:    
  Maximum force on spring, Fmax:    
  Minimum force on spring, Fmin:    
  Wire diameter, d:    
  Outer diameter of spring, Douter:    
  Material's limiting fatigue stress:    
  Material's yield stress:    
  Factor of safety:    
Answers
  Minimum length of spring (under Fmax):  3.85  in
  Mean component of shear, tmean:  13.4  ksi
  Alternating component of shear, talt:  2.68  ksi
  Soderberg limit for talt:  3.91  ksi
 
Fatigue Check:  Your spring is safe from fatigue.
Equations Behind the Calculator
See the companion page to view the equations for this calculator.
STEM Career Outlook

Wages, employment opportunities, and growth projections for STEM jobs.

Metal 3D Printing Design Guide

Direct Metal Laser Sintering (DMLS) 3D printing for parts with reduced cost and little waste.

3D Scanners

A white paper to assist in the evaluation of 3D scanning hardware solutions.

CNC Machining Design Guide

Optimize your designs, reduce machining time, and lower your costs.