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AFGROW | DTD Handbook

Handbook for Damage Tolerant Design

  • DTDHandbook
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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 Analysis of Intact Structure–Residual Strength Guidelines and Damage Growth Limits

The specific set of guidelines for intact structure depends upon the capability of the depot level inspection.  Since this example has assumed the situation where the normal inspection can detect less than a failed load path, this case will be examined first.

The intact requirement is that the in-service damage, assumed to be present following the depot level inspection (Figure 1.3.17), shall not grow and cause failure of the major load path (panel ­) before the next opportunity to discover the damage, i.e., the next inspection.

Since this is merely a one-time design requirement, not specifically intended for safety, it is not necessary to account for prior service at the time at which the requirement was imposed.  Thus, the structure is considered as “new” and no incremental growth Da due to prior service is computed.  Figure 1.3.18 illustrates schematically the residual strength and growth guidelines that must be met for the intact structure.


Figure 1.3.18.  Illustration of Damage-Growth Limits and Residual-Strength for Intact Structure Following Depot or Base-Level Inspection for Less-Than-Failed Load Path