Fatigue Life Calculator
Calculate cycles to failure using the S-N curve: N = (S_e / S_a)^(1/b). Enter stress amplitude, endurance limit, and fatigue exponent.
How to Use the Fatigue Life Calculator
- Enter the operating stress amplitude in MPa.
- Enter the material endurance limit in MPa.
- Enter the fatigue exponent b (negative number, e.g. −0.1).
Use Cases
- •Predicting component life under cyclic loading.
- •Designing aerospace and automotive parts.
- •Assessing fatigue life of welds and fasteners.
Formula
N = (S_e / S_a)^(1/b), where N is cycles to failure, S_e is endurance limit (MPa), S_a is stress amplitude (MPa), b is the fatigue exponent (typically −0.05 to −0.15).
Frequently Asked Questions
What is the S-N curve?
The S-N curve (Wöhler curve) plots cycles to failure against stress amplitude. Lower stress means longer component life.
What is the fatigue exponent b?
The fatigue exponent b is a negative number describing the slope of the S-N curve. For steels b ≈ −0.1; for aluminium b ≈ −0.07 to −0.14.
What is the endurance limit?
The endurance limit (S_e) is the stress below which a material theoretically has infinite fatigue life. For steels S_e ≈ 0.5 × σ_uts.