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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
        • 0. Residual Strength
        • 1. Introduction
        • 2. Failure Criteria
          • 0. Failure Criteria
          • 1. Ultimate Strength
          • 2. Fracture Toughness - Abrupt Fracture
          • 3. Crack Growth Resistance – Tearing Fracture
        • 3. Residual Strength Capability
        • 4. Single Load Path Structure
        • 5. Built-Up Structures
        • 6. References
      • 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 4.2.1. Ultimate Strength

4.2.1         Ultimate Strength

The simplest failure criterion assumes that failure occurs at the ultimate (or yield) strength of the material.  Thus, the failure criterion becomes simply

sf = Ftu

(4.2.1)

where sf is the fracture stress and Ftu is the ultimate strength.  This criterion is applicable primarily to uncracked structures and is included here for completeness.  In past analyses of failure of built-up structure, the residual strength of stiffeners was based upon this criterion.  When the main panel between the stiffeners fails due to catastrophic crack growth, the panel loads are transferred to the stringers (or stiffeners).  The transferred loads may increase the stress level in the stringer so it is high enough to reach the value of sf, causing stiffener failure.