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DTD Handbook

Handbook for Damage Tolerant Design

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    • About
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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
            • 0. Required Periods Of Safe Damage Growth
            • 1. Slow Crack Growth Structure
            • 2. Fail Safe Multiple Load Path Structure
            • 3. Fail Safe Crack Arrest Structures
          • 7. Illustrative Example Of Guidelines
        • 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 1.3.6.3. Fail Safe Crack Arrest Structures

Fail safe crack arrest structure must be able to withstand a specified period of service usage after a primary load path failure.  The period of unrepaired service usage depends upon the inspectability level for the structure.  The degrees of inspectability for fail safe crack arrest structure are the same as for fail safe multiple load path structures.

The initial inspection intervals are given in Table 1.3.5, and subsequent inspection intervals are given in Table 1.3.6.

Table 1.3.6.  Subsequent In-Service Inspection Intervals for Fail-Safe Structures

Primary Element Degree of Inspectability

Pxx

Subsequent Inspection Intervals

In-Flight Evident

PFE

Each flight of most damaging design mission

Ground Evident

PGE

Two flights of most damaging design mission

Walk-Around Visual

PWV

Ten flights of most damaging design mission

Special Visual

PSV

One year

Depot or Base Level

PDM

One half of the remaining time to failure of the adjacent structure from the flaw size specified for adjacent load paths at the time of primary element failure; or, if the adjacent structure  is inspected, one half  of the remaining time to failure of the adjacent structure from in-service inspection flaw size for the adjacent structure as specified.  In either case, the primary element is assumed to be failed.