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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
          • 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

Section 1.3.7.2.3. In-Service Flaw Assumptions Following Inspection

The capability of inspection in the field is generally less than at the depot.  The sizes of damage assumed to exist following inspection are specified in JSSG-2006 paragraph A3.12.1.  For this example, assume that penetrant or ultrasonics will be used at the depot both exterior and interior to the lower surface.  If this type of inspection is conducted, the damage likely to be found will be much smaller than the failed skin panel.  From JSSG-2006 Table XXXII the minimum damage size to be assumed is a through crack of 0.25 inch uncovered length.  The locations of the 0.25 inch length both in the skin and in the splicing stringer should be selected on the basis of inspectability but should be the location most critical to subsequent growth.  Assume for purposes of illustration, that the damage is as indicated in Figure 1.3.17.  The 0.005 inch flaw away from the primary damage site represents the initial manufacturing type damage as specified in JSSG-2006 paragraph A3.12.1.