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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
      • 8. Force Management and Sustainment Engineering
      • 9. Structural Repairs
      • 10. Guidelines for Damage Tolerance Design and Fracture Control Planning
        • 0. Guidelines for Damage Tolerance Design and Fracture Control Planning
        • 1. Design Loads Spectrum
        • 2. Material Selection
        • 3. Structural Configuration Analysis
          • 0. Structural Configuration Analysis
          • 1. Critical Parts List
          • 2. Inspection Method Development
          • 3. Demonstration Test Development
        • 4. Manufacturing Process
        • 5. References
      • 11. Summary of Stress Intensity Factor Information
    • Examples

Section 10.3.2. Inspection Method Development

During the development of the critical parts list, it is necessary to consider how each part will be inspected for flaws.  This must be considered not only during the manufacturing process but also during the periodic inspections to be performed during the aircraft life.  The results of the fracture analysis can be significantly affected by the inspection method and the selection of initial flaw sizes.

As improved inspection methods are incorporated into production use, it is to be expected that improved design will result.  The trade-off between inspection costs and performance may also be considered.

Table 10.3.1.  Examples Of NDE Capabilities [Ehert, 1979]

Inspection Method

Flaw Type

Standard NDE

Special NDE

Penetrant or magnetic particle

Surface flaw
(Depth x length)

0.19 x 0.38 cm
(0.075 x 0.150 in.) or equivalent area

0.083 x 0.127 cm
(0.025 x 0.050 in.) or equivalent area

Ultrasonics

Embedded flaw (diameter)

0.254 cm (0.100 in.)

0.12 cm (0.047 in.)

Radiographic

Surface or embedded (depth x length)

0.7t x 1.4t
Min length = 0.38 cm  (0.150 in.)

0.6t x 1.2t
Min length = 0.127 cm (0.050 in.)

t = thickness