Failure under repeated or varying load WHICH is never sufficient to cause failure in a single application
Assessing fatigue damage of complicated structural shape is difficult

• Difficulty in determining stress variation when the stress flow changes directions abruptly

Three ways to deal :

• Modeling in finite elements
• Using stress concentration factors
  - approach for tubular joints
  - parametric equations developed by authors based on FEM
  - vary with geometry of joint & load application

Fatigue evaluation through

• Deterministic Fatigue Approach
• Spectral Analysis Approach