r7.04.02 Estimation of fatigue under random stress

Summary:

This note presents two methods for counting stress cycles that lead to an analytical expression of the mechanical damage caused by a random loading:

• method for counting stress peaks,

• method for counting violations of a given level.

The first method uses the signal, its first derivative and its second derivative. The second requires only knowledge of the signal and its first derivative.

Since stress cycles are known by these methods, the average damage over the duration of the signal is determined using the Wöhler method.

• 1. Introduction
• 2. Damage assessment
  • 2.1. Endurance diagram
  • 2.2. Elasto-plastic concentration coefficient
• 3. Number of stress cycles
  • 3.1. Reminders: spectral moments and the irregularity factor
  • 3.2. Method for counting stress peaks
  • 3.3. Method for counting level breaches
• 4. Statistical estimation of damage
  • 4.1. Average damage
• 5. Conclusion
• 6. Bibliography
• 7. Description of document versions