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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
            • 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 1.3.6.0. Required Periods Of Safe Damage Growth

The required period of safe damage growth is a function of design category (either slow crack growth or fail safe) and the degree of inspectability as defined in Section 1.3.3.  In order to cover various uncertainties associated with crack growth during service usage that may not be adequately accounted for in the analyses or laboratory test, the structure must withstand a period of service usage longer than the planned inspection interval.  The periods of unrepaired service usage for the inspectability categories is given in JSSG-2006 Table XXXIII and repeated in Table 1.3.5.

Table 1.3.5.  Minimum Periods of Unrepaired Service Usage for In-Service Inspectable Structures

Degree of Inspectability

Pxx

Minimum Period of Unrepaired Service Usage

In-Flight Evident

PFE

Return to base

Ground Evident

PGE

Two flights of most damaging design mission

Walk-Around Visual

PWV

5 ´ Inspection interval (= 5´10 flights)

Special Visual

PSV

2 ´ Inspection interval (= 2´ one year)

Depot or Base Level

PDM

2 ´ Inspection interval (= 2´ ¼ lifetimes)