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DTD Handbook

Handbook for Damage Tolerant Design

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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
            • 0. Initial Damage Assumptions
            • 1. Intact Structure Primary Damage Assumption
            • 2. Continuing Damage
            • 3. Fastener Policy
            • 4. In-Service Inspection Damage Assumptions
            • 5. Demonstration of Initial Flaw Sizes Smaller Than Those Specified
          • 5. Residual Strength Guidelines
          • 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 1.3.4.0. Initial Damage Assumptions

JSSG-2006 paragraph A3.12.1 assumes that any fastener hole in the structure can be marginal and can have an initial damage equivalent to a 0.005 inch radius corner flaw.  Thus, the guidelines requires assuming that this flaw exists at each fastener hole within the structure at the time of manufacture.  Since the 0.005 inch size is based on limited data, the contractor may provide data representing his own manufacturing quality and negotiate with the Air Force for a smaller size of the apparent initial flaw to represent marginal hole quality.

The most critical location for the initial flaw should be determined by reviewing all elements of the structure and considering features such as edges, fillets, holes, and other high stressed areas.