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AFGROW | 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
          • 5. Residual Strength Guidelines
          • 6. Required Periods Of Safe Damage Growth
          • 7. Illustrative Example Of Guidelines
            • 0. Illustrative Example Of Guidelines
            • 1. Slow Crack Growth Structure
            • 2. Fail Safe Structure
              • 0. Fail Safe Structure
              • 1. In-Service Inspection Consideration
              • 2. Initial Flaw Considerations
              • 3. In-Service Flaw Assumptions Following Inspection
              • 4. Adjacent Structure Damage Following the Failure of the Major Load Path
              • 5. Analysis of Intact Structure–Residual Strength Guidelines and Damage Growth Limits
              • 6. Analysis of Intact Structure (Alternate Requirement)
              • 7. Discussion of Intact Structure Analysis
              • 8. Analysis of Remaining Structure Subsequent to Load Path Failure
              • 9. Derivation of Residual Strength Load
              • 10. Incremental Damage Growth Da
              • 11. Alternative-Analysis of Remaining Structure Subsequent to Load Path Failure
              • 12. Summary and Comments
        • 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
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Section 1.3.7.2.2. Initial Flaw Considerations

Flaws assumed to result from manufacturing and/or material conditions are specified in JSSG-2006 paragraph A3.12.2 for Fail Safe Structure.  The primary damage at a fastener hole (Figure 1.3.16) is an 0.05 inch corner flaw.  Since the drilling operation is common to the skin and splicing stringer, the 0.05 inch flaw must be assumed in both members.  Panel ­ is considered for this example because it was previously chosen to be the critical load path.  Note that only one primary damage site is assumed for each load path (e.g. along the path of expected damage, along a wing section).  Also, it is not necessary to consider the interaction of flaws from adjacent primary sites.  Each analysis of primary damage is conducted independently.  At each hole other than the assumed primary site, an 0.005 inch radius corner flaw is assumed to represent average or typical manufacturing quality.  The effect of interactions between the 0.005 inch flaws and the primary flaws must be considered when conducting the analysis.

Figure 1.3.16.  Initial-Flaw Assumptions for Example Case Qualified as Fail Safe


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