// multi-utility computation suite · offline · instant · precise
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sci.fatigue-sn-curve Calculator
Calculates fatigue life (cycles to failure) from stress amplitude using the S-N curve and Basquin power law. Steel has an endurance limit ~40–60% of UTS — below this stress amplitude it can theoretically endure infinite cycles; aluminium has no true endurance limit.
Inputs
Stress Amplitude Mpa
Maximum displacement from equilibrium. Energy carried by a wave is proportional to amplitude squared.
Ultimate Strength Mpa
Maximum stress before fracture. Structural steel: 400–700 MPa. Aluminium alloys: 200–500 MPa.
Surface Factor
A multiplier applied in the calculation.
Size Factor
A multiplier applied in the calculation.
Results
cycles to failure estimate
The value at the specified point or condition.
endurance limit Se (MPa)
Sample size or count used in the calculation.
S_e prime (0.5Sut)
Reference formula or conversion factor shown for context.
Basquin slope b
The gradient -- rise divided by run. In finance, rate of change per unit time.
Marin factors applied
A dimensionless multiplier applied in the calculation.
stress ratio R=-1
Internal force per unit area (Pa or MPa). Must stay below yield strength in service. Beyond yield: permanent deformation. Beyond tensile strength: fracture.