Metal Fatigue
Subject
Fatigue is the premature deterioration and/or failure of a material due to repeated stress variations. If allowed to continue unchecked, it can destroy a component quickly and unpredictably.
Every moving part is exposed to fluctuating stresses, if these stresses are kept well below 50% of yield stress, it is not normally necessary to address for fatigue, otherwise it is essential to ensure that design life is not compromised due to premature failure.
Calculator
Fatigue has been designed to calculate the fatigue life of a mechanical component according to three recognised theories: Linear, NonLinear and NonZero MultiAxial Mean.
Linear & NonLinear calculation options compare the actual number of stress cycles with the allowable number of stress cycles for each stressblock in its design life.
NonZero MultiAxial Mean compares extreme design stress ranges against a special diagram developed by John Goodman to determine compliance with allowable stresses for the material.
The metal fatigue calculator also provides for a userdefined SN curve. This diagram is required for the solution of the 'Linear' and 'NonLinear' calculation methods but is not required for the 'NonZero MultiAxial Mean' method.
For help using this calculator see Technical Help
Metal Fatigue Calculator  Options
SN Curve
This is a plot of maximum allowable stress range against maximum permitted number of cycles. The output data from this SN curve is used in the Linear and NonLinear calculation procedures.
You enter: 
and the metal fatigue calculator will provide: 


Slope (information only)

Theoretical axis intersection (information only)

NonLinear
This method uses the Weibull Parameter and the Gamma Function to compare a userdefined stressblock with the mostdamaging stressblock.
You enter: 
and the metal fatigue calculator will provide: 


Damage Ratio for the user defined stressblock

Weibull parameter (information only)

Gamma Function (information only)

Linear
This method (also known as the Palmgren–Miner technique) is a simple sum of ratios for each stressblock in the life of the component. Fatigue provides input for seven stressblocks.
You enter: 
and the metal fatigue calculator will provide: 


Damage Ratio all stressblock (combined)

NonZero MultiAxial Mean
Fatigue looks to see if your maximum design stress ranges fall within the parameters of Goodman’s modified diagram.
You enter: 
and the metal fatigue calculator will provide: 


‘ok’ or a ‘fail’ condition for the principal stresses, shear stresses and strain energy

Check minimum system requirements