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DTD Handbook

Handbook for Damage Tolerant Design

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    • Sections
      • 1. Introduction
      • 2. Fundamentals of Damage Tolerance
      • 3. Damage Size Characterizations
      • 4. Residual Strength
      • 5. Analysis Of Damage Growth
        • 0. Analysis Of Damage Growth
        • 2. Variable-Amplitude Loading
          • 0. Variable-Amplitude Loading
          • 1. Retardation
          • 2. Integration Routines
          • 3. Cycle-by-Cycle Analysis
        • 3. Small Crack Behavior
        • 4. Stress Sequence Development
        • 5. Crack Growth Prediction
        • 6. References
      • 6. Examples of Damage Tolerant Analyses
      • 7. Damage Tolerance Testing
      • 8. Force Management and Sustainment Engineering
      • 9. Structural Repairs
      • 10. Guidelines for Damage Tolerance Design and Fracture Control Planning
      • 11. Summary of Stress Intensity Factor Information
    • Examples

Section 5.2.0. Variable-Amplitude Loading

Baseline fatigue data are derived under constant-amplitude loading conditions, but aircraft components are subjected to variable amplitude loading.  If there were not interaction effects of high and low loads in the sequence, it would be relatively easy to establish a crack-growth curve by means of a cycle-by-cycle integration.  However, interaction effects of high and low loads largely complicate crack-growth under variable-amplitude cycling.

In the following sections these interaction effects will be briefly discussed.  Crack growth-prediction procedures that take interaction effects into account will be presented in Section 5.2.3.