How to Calculate Fatigue Life
What is Fatigue Life?
Fatigue life estimation predicts component life under cyclic loading. Failure occurs at stress levels well below static strength.
Step-by-Step Guide
- 1Use S-N curves or Miner's rule for fatigue analysis
- 2Calculate stress range and mean stress effects
- 3Account for surface finish, size, and stress concentration
Worked Examples
Input
Stress range 200 MPa, material steel, 10⁶ cycle life, actual 5×10⁸ cycles required
Result
Life exceeded; fatigue safe
Approximate S-N curve lookup
Common Mistakes to Avoid
- ✕Using static stress limits for cyclic loading
- ✕Neglecting size effect on fatigue strength
Frequently Asked Questions
What is endurance limit?
Maximum stress below which infinite life is achieved (for steel ~0.5 × ultimate strength).
How do stress concentrations affect fatigue?
Stress concentrations reduce fatigue strength significantly; notches and holes are critical.
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