Metal Fatigue Calculator v1

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.

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)

Non-Linear

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)

Linear

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

Check minimum system requirements