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Stiffened Panels

Validation of stiffened panel analysis — fatigue crack growth retardation by stiffeners and residual strength with rivet yielding.

7.1 Fatigue Crack Propagation in Stiffened Panels

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Based on Poe's reference work (Damage Tolerance in Aircraft Structures). An 84-inch (2,134 mm) wide aluminum panel with bolted stringers spaced at 6 inches (152 mm), ¼-inch Hi-Lok lockbolts at 1-inch pitch, skin thickness 0.090 inches (2.29 mm).

The stiffening ratio is defined as: μ = (Ast Est) / (A E + Ast Est)

μ = 0.21

Fatigue Crack Propagation in Stiffened Panels Panel with Bolted Stringers, mu = 0.21, Stringers Spaced 152 mm XdTd vs Test Results

μ = 0.58

Fatigue Crack Propagation in Stiffened Panels Lockbolted Stringers, mu = 0.58, Stringers Spaced 152 mm XdTd vs Test Results

7.2 Stiffened Panel Residual Strength

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Based on T. Swift's work (The Effects of Rivet Yielding on Fracture Strength of Stiffened Structures Containing Cracks, McDonnell Douglas). This benchmark demonstrates that elastic analysis alone is inadequate — elastic-plastic rivet behavior with deformation limits must be modeled.

Stiffened Panel Residual Strength Stress-Strain Curve for Riveted Attachments Used in Tests vs XdTd Model Results for Rigid Rivet Behaviour Results for Elastic Rivet Behaviour Results for Elastic-Plastic Rivet Behaviour Final Results - Elastic-Plastic Rivet Behaviour with Attachment Deformation Limit XdTd Predicted Panel Failure Mode - Attachment Line Failure at 253 mm vs 251 mm in Test Results Are Very Sensitive to the Stress-Strain Model Tom Swift Was Right - This Problem Cannot Be Assessed by Elastic Analysis

XdTd accurately predicted:

  • The failure mode: rivet line of the crack-arresting stiffener
  • The critical crack length: 252 mm (vs. 251 mm from the panel test)