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AFGROW | DTD Handbook

Handbook for Damage Tolerant Design

  • DTDHandbook
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    • Sections
      • 1. Introduction
      • 2. Fundamentals of Damage Tolerance
      • 3. Damage Size Characterizations
      • 4. Residual Strength
      • 5. Analysis Of Damage Growth
      • 6. Examples of Damage Tolerant Analyses
      • 7. Damage Tolerance Testing
        • 0. Damage Tolerance Testing
        • 1. Introduction
        • 2. Material Tests
        • 3. Quality Control Testing
        • 4. Analysis Verification Testing
        • 5. Structural Hardware Tests
          • 0. Structural Hardware Tests
          • 1. Test Conditions
          • 2. Initial and Continuing Damage
          • 3. Residual Strength Testing
          • 4. Damage Tolerance Test Articles
          • 5. Evaluation and Interpretation of Test Results
        • 6. References
      • 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 7.5.3. Residual Strength Testing

Residual strength tests of fail safe structure are of special importance.  Interruption of a fatigue test at the critical crack size for intact structure is crucial.  If the crack grows longer, the stress for rapid propagation is too low to give proper information on crack arrest capabilities and on the strength of the remaining structure at that stress (times the dynamic factor).  Since these properties are essential for the qualification as fail safe structure, a proper evaluation is justified, even during design development tests.

After instability and arrest (or load path failure), if successful, fatigue testing should be continued.  At that point the JSSG-2006 Damage Tolerance Requirements assume remaining structure damage.  In testing, this poses the same problems as the continuing damage.  Therefore, it is recommended that the remaining structure damage be developed in a natural way during damage tolerance testing; artificially induced damage may also be incorporated where necessary consistent with the initial flaw assumptions of the component.  Again, fatigue cycling is discontinued when the (calculated) critical size for the remaining structure damage is reached.  Then a final residual strength test is performed.