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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
              • 0. Slow Crack Growth Structure
              • 1. Initial Flaw Sizes Assumed to Result from Manufacturing
              • 2. Choice of Inspection Category
              • 3. In-Service Non-Inspectable Category
              • 4. Depot Level Inspectable Category
            • 2. Fail Safe Structure
        • 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 1.3.7.1.1. Initial Flaw Sizes Assumed to Result from Manufacturing

The assumed flaws for the slow crack growth type structure are described in Section 1.3.4.  Thus, an 0.050 inch corner flaw is assumed to exist at the critical fastener hole joining panel ­ and the splicing stringer, as shown in Figure 1.3.12.  For this example, it is assumed that a common drilling operation was employed to prepare the hole with the primary damage, and therefore the same size crack is assumed in both elements.  Also, as explained in Section 1.3.4, initial flaws equivalent in stress-intensity factor level to an 0.005 inch radius corner flaw shall be assumed to exist in each hole of each element in the structure, such as shown in Figure 1.3.12.

Figure 1.3.12.  Illustration of Initial Flaws for Structure Qualified as Fail-Safe Multiple Load Path