Application of Cohesive Elements to Predict Lead Failure Behaviors in Bonded Composite T-Joints under Two Load Cases

A numerical modeling study was conducted to assess the effectiveness of cohesive elements in predicting lead failure behavior of bonded laminated composite T-joints. Static failure test results were used to validate the modeling predictions for three joint conditions: pristine, tip defect, and throat defect, under two load cases: pulling and side-bend. The analyses were carried out in two phases: a blind modeling phase without knowing the test results, and a refinement phase using adjusted cohesive strengths and/or revised models informed by the test findings. A half-width model was used in the blind modeling analyses to take advantage of the symmetricity in the joint structure, whereas a unit-width model under plane stress or plane strain conditions was adopted in the refinement phase. The unit-width model approach achieved comparable accuracy with using only approximately 5% of the computational time required for the half-width model. Cohesive zone locations in the blind prediction models were determined through preliminary simulations, and additional zones were introduced in the revised models for the side-bend loading. The results showed good agreement between tests, blind modeling, and refinement analyses in terms of stiffness and strength for the pulling load case. For the side-bend load case, stiffness predictions were consistent across tests and all numerical analyses. The refined analyses successfully reproduced the observed test failure modes under both loading conditions. Discrepancies in both the joint strength and the failure characteristics among tests and simulations were analyzed and are discussed in this paper. Given the no-growth assumption for safe composite aircraft structures, the current numerical analysis approach reasonably predicted joint strengths and the lead failure behaviors.