A process where a material (or structure) fails because of progressive crack growth due to repeated cyclic stress. The cyclic stress is usually considerably below the material's yield strength.

Many factors affect the fatigue process. (See Juvinall, pp. 193 - 369.) These factors include:

  1. The material.
  2. The material's processing history.
  3. The method of stress application (axial, bending, rotating bending, etc.).
  4. The stress level (which is influenced by geometry).
  5. The presence of residual stresses or static stresses.
  6. The material's notch sensitivity.
  7. The test frequency.
  8. The test direction relative to the material's grain direction.
  9. The size of the raw stock from which the sample has been machined.
  10. The surface finish.
  11. Plating.
  12. The environment (including temperature, humidity, corrosives, etc.).

Thus, caution must be used when determining fatigue performance.

Fatigue is the most common failure mode for horns and boosters.

Also see —
Fatigue life (N)
Fatigue limit
Fatigue notch factor (Kf)
Fatigue notch sensitivity (q)
Fatigue strength
Fatigue test
Fatigue test horn
Gerber parabola
S‑N curve
S‑N test