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DTD Handbook

Handbook for Damage Tolerant Design

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    • Sections
      • 1. Introduction
      • 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
        • 0. Damage Tolerance Testing
        • 1. Introduction
        • 2. Material Tests
        • 3. Quality Control Testing
        • 4. Analysis Verification Testing
        • 5. Structural Hardware Tests
          • 0. Structural Hardware Tests
          • 1. Test Conditions
          • 2. Initial and Continuing Damage
          • 3. Residual Strength Testing
          • 4. Damage Tolerance Test Articles
          • 5. Evaluation and Interpretation of Test Results
        • 6. References
      • 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 7.5.4. Damage Tolerance Test Articles

During the development cycle, the manufacturer will subject major assemblies and structural components to flight-by-flight fatigue loadings that approximate the operational environment.  Some tests are specifically identified as damage tolerant tests or as durability tests, but other tests serve a dual function - first as a durability test (two lifetimes) and then as a damage tolerant test. Component durability tests or component dual function tests are normally scheduled to precede the full-scale durability test by a sufficient amount of time that would allow incorporating suggested structural modifications into the full-scale durability test article.  The scheduling of the full scale damage tolerant test follows (and uses) the full scale durability test article.

The major assemblies and components selected for damage tolerant testing are chosen to provide further assurance that major elements will not fail during service and thus impact the operational readiness of the force due to safety-of-flight failures.  Several examples of major assemblies and components selected during recent weapon system acquisition programs are listed in Table 7.5.1.

The damage tolerant articles will include artificially induced damage such as scratches, elox notches, sawcuts, and other types of non-crack damage, and are then subjected to an interval (about one-quarter lifetime) of flight-by-flight loading that is designed to initiate the desired starter cracks.  The test interval subsequent to the precracking is up to one design lifetime with a Pxx loading applied at the end of the lifetime to verify residual strength capability.  Crack growth should be monitored throughout the test.  In-service inspection procedures should be employed whenever possible to evaluate the ability of these procedures to locate and measure the cracks.

Table 7.5.1.  Major Assemblies and Components Tested to Support

Damage Tolerant Design Verification

F–16

A–10

B–1A

KC–10

Wing/Fuselage Box Beam Components

Wing Lower Center Panel

Wing Carry Through Article*

Fuel Tank Panel and Fuselage Floor Beam Structure

Horizontal Tail Component

Engine/Nacelle Forward Support Frame Fuselage Support Lug

Aft Fuselage Article*

Aerial Refueling Boom

 

Horizontal Tail Support Aft Frame Fitting and Attachment Lug

 

 

 

Nacelle Thrust Fitting Assembly

 

 

* Damaged subsequent to durability test (2 lifetimes).