Fatigue Life Estimation
Estimated Cycles to Failure
-
Fatigue Regime
-
Stress Amplitude
-
Mean Stress
-
Stress Ratio
-
Calculation Method
-
Interpretation:
Enter parameters and click "Calculate" to get results.
Usage Notes
  • For most accurate results, use material-specific S-N curve data.
  • High-cycle fatigue typically occurs above 10,000 cycles.
  • Consider mean stress effects for more precise estimations.
  • Results are estimates - always validate with experimental data.
Fatigue Life Estimation Theory

Basquin's law describes the relationship between stress amplitude and number of cycles to failure:

σₐ = σ′f × (2N)b

Where:

  • σₐ = Stress amplitude
  • σ′f = Fatigue strength coefficient
  • N = Number of cycles to failure
  • b = Fatigue strength exponent (slope of S-N curve)

This equation can be rearranged to solve for N:

N = (σₐ/σ′f)1/b ÷ 2

S-N curves (Stress-Number of cycles) are graphical representations of a material's fatigue behavior.

Key characteristics:

  • X-axis: Number of cycles (log scale)
  • Y-axis: Stress amplitude (log scale)
  • For ferrous metals: Curve flattens at endurance limit
  • For non-ferrous metals: Curve continues to decline
S-N Curve Example

Regime Cycles Range Characteristics
Low-cycle fatigue 10 - 104 Plastic deformation, strain-controlled
High-cycle fatigue 104 - 107 Elastic deformation, stress-controlled
Infinite life > 107 Below endurance limit (for materials that have one)