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DTD Handbook

Handbook for Damage Tolerant Design

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    • About
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    • Sections
      • 1. Introduction
        • 0. Introduction
        • 1. Historical Perspective on Structural Integrity in the USAF
        • 2. Overview of MIL-HDBK-1530 ASIP Guidance
        • 3. Summary of Damage Tolerance Design Guidelines
          • 0. Summary of Damage Tolerance Design Guidelines
          • 1. Summary of Guidelines
          • 2. Design Category
          • 3. Inspection Categories and Inspection Intervals
          • 4. Initial Damage Assumptions
          • 5. Residual Strength Guidelines
            • 0. Residual Strength Guidelines
            • 1. Fail-Safe Structure at Time of Load Path Failure
            • 2. Determining the Residual Strength Load for Remaining Structure
          • 6. Required Periods Of Safe Damage Growth
          • 7. Illustrative Example Of Guidelines
        • 4. Sustainment/Aging Aircraft
        • 5. References
      • 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
      • 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 Fail-Safe Structure at Time of Load Path Failure

For Fail Safe Structure, there is a requirement that the remaining structure at the time of a single load path failure must be capable of withstanding a minimum load Pyy.  This load Pyy is at least the load that causes the load path failure, plus an additional increment to account for the dynamic conditions of the breaking member.  While most data and analyses indicate that the dynamic magnification factor associated with the member failure is probably very small, the current guidance in JSSG-2006 requires that a 1.15 dynamic factor be applied to the redistributed incremental load unless another value is determined by test or analysis.  For non-metallic structure, the dynamic factor should be verified by testing.  Figure 1.3.9 illustrates the change in residual strength guidelines as a result of a load path failure.


Figure 1.3.9.  Schematic Residual Strength Guidelines for Fail Safe Structure