Out-of-plane coupling effects on stress intensity factors at interface cracks in composite lap joints

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Abstract

The existence of off-axis plies in adhesively bonded lap joints leads to anisotropic stress-strain relationships where the in-plane and out-of-plane components of stress and deformation (in a plane perpendicular to the width of the joint) are coupled. In this paper, the anisotropic elasticity solution near a bimaterial crack tip is formulated using an eigenfunction expansion of the stresses and displacements. This elasticity solution is subsequently used in conjunction with finite elements in a global/local method in order to determine mode I, mode II, and mode III stress intensity factors. Numerical results for [(±Θ)2]s layups indicated that an out-of-plane mode III stress intensity factor, KIII, arises when off-axis plies are present even though the loading is in-plane. Depending on the layup angle and crack location, KIII can be as large as 43% of KI and 55% KII. It was also found that, in addition to producing a mode III intensity factor, out-of-plane coupling affects the magnitude of the in-plane stress intensity factors, KI and KII. Comparison of the 3D results with a 2D solution indicated that, depending on the layup angle, the 2D solution can either overpredict or underpredict the values of KI and KII by as much as 35%. Finally, the use of an effective stress intensity factor with thermoplastic or thermoset composites indicated that the 2D solution can overestimate failure loads by as much as 36% and corroborated the experimental observation that failure in composite bonded joints generally occurs as a first-ply failure of the adherends.

Original languageEnglish (US)
Pages (from-to)178-200
Number of pages23
JournalJournal of Thermoplastic Composite Materials
Volume14
Issue number3
DOIs
StatePublished - May 1 2001

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Keywords

  • Bimaterial interfaces
  • Bonded joints
  • Fracture mechanics
  • Interlaminar cracks
  • Off-axis plies
  • Out-of-plane coupling
  • Stress intensity factors
  • Stress singularities
  • Three-dimensional effects

ASJC Scopus subject areas

  • Ceramics and Composites
  • Condensed Matter Physics

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