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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 1.3.7.2.8. Analysis of Remaining Structure Subsequent to Load Path Failure

The fail safe characteristics of this structure, i.e., the ability to fail panel ­ and fly safely until the failed panel is detected, depends upon the residual strength capability at the time of and subsequent to load path failure and the capability of and frequency of in-service inspections.  The remaining structure guidelines are specified in JSSG-2006 paragraph A3.12.2.2. 

As stated earlier, the fail safety will be supported by walk-around-visual inspections for damage sizes on the order of a failed load path.  Generally, the walk-around-visual inspection can be aided by detectable signs such as fuel leakage.  At any rate, the minimum inspection capability for this example will be considered to be a failed load path.

The damage as illustrated in Figure 1.3.17 shall not grow to a size such as to cause loss of the wing due to the application of PVW in 5 times the inspection interval (10 flights), i.e. in 50 flights.  This is illustrated in Figure 1.3.20.  The load Pxx = Pyy will generally be less than the design limit condition and Pyy (as discussed in Section 2.5) will always be equal to or greater than that associated with the design limit condition.

 

Figure 1.3.20.  Illustration of Damage-Growth Limits and Strength Guidelines; Remaining Structure Subsequent to Load-Path Failure


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