Free Fatigue Life Calculator
Estimate the number of load cycles to failure using a simplified S-N curve approach (Basquin relation).
Cycles to Failure (Nf)
3,405,063 cycles
Cycles to Failure (Nf) vs Stress Amplitude (Sa)
Fatigue Life Estimation (Basquin Relation)
Repetitive loading below the static strength can cause failure through fatigue crack growth.
Formula
Sa = Sf' (2Nf)^b or equivalently Nf = 0.5 (Sa / Sf')^(1/b)
This simplified form (Basquin equation) relates stress amplitude Sa to cycles to failure Nf. The fatigue strength coefficient Sf' and exponent b are material properties obtained from testing. Typical b values range from -0.05 to -0.15.
Example Calculation
A steel component with Sf'=900 MPa, b=-0.1, subjected to 200 MPa stress amplitude.
- 01Sa/Sf' = 200/900 = 0.2222
- 021/b = 1/(-0.1) = -10
- 03Nf = (0.2222)^(-10) = approximately 6,046,618 cycles
- 04This is above 10^6, suggesting effectively infinite life for many applications.
Frequently Asked Questions
Learn More
Beam Stress Calculation Guide: From Theory to Practice
Learn how to calculate beam stress step by step. Covers bending stress, shear stress, the flexure formula, stress distributions, and practical design checks for structural beams.