Metal Fatigue Calculator v1

Price: £25.41 (£25.41 Inc. VAT)
Structural fatigue calculator


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.


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Fatigue has been designed to calculate the fatigue life of a mechanical component according to three recognised theories: Linear, Non-Linear and Non-Zero Multi-Axial Mean.

Linear & Non-Linear calculation options compare the actual number of stress cycles with the allowable number of stress cycles for each stress-block in its design life.

Non-Zero Multi-Axial 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 user-defined S-N curve. This diagram is required for the solution of the 'Linear' and 'Non-Linear' calculation methods but is not required for the 'Non-Zero Multi-Axial Mean' method.

For help using this calculator see Technical Help

Metal Fatigue Calculator - Options

S-N Curve

This is a plot of maximum allowable stress range against maximum permitted number of cycles. The output data from this S-N curve is used in the Linear and Non-Linear calculation procedures.

You enter: and the metal fatigue calculator will provide:
  • The co-ordinates of each end of the curve
  • Slope (information only)
  • Theoretical axis intersection (information only)


This method uses the Weibull Parameter and the Gamma Function to compare a user-defined stress-block with the most-damaging stress-block.

You enter: and the metal fatigue calculator will provide:
  • Stress range from the most damaging stress-block
  • Total number of stress cycles that represent the fatigue life of the component
  • Stress range and associated cycles for a given stress-block
  • Damage Ratio for the user defined stress-block
  • Weibull parameter (information only)
  • Gamma Function (information only)


This method (also known as the Palmgren–Miner technique) is a simple sum of ratios for each stress-block in the life of the component. Fatigue provides input for seven stress-blocks.

You enter: and the metal fatigue calculator will provide:
  • Stress range for each stress-block
  • Number of stress cycles for each stress-block
  • Damage Ratio all stress-block (combined)

Non-Zero Multi-Axial 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:
  • Maximum and minimum principal stresses in each 3D plane
  • Minimum specified yield stress
  • Ultimate tensile stress
  • Young’s modulus for the material
  • Maximum allowable number of stress cycles that will provide an infinite design life
  • ‘ok’ or a ‘fail’ condition for the principal stresses, shear stresses and strain energy

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