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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.
Injection Molding Design Guide

Guide for high quality and cost-effective plastic injection molding.

Negotiate Your Salary

Learn the best principles to negotiate the salary you deserve!

Essentials of Manufacturing

Information, coverage of important developments and expert commentary in manufacturing.

Metal 3D Printing Design Guide

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