Progressive Failure Analysis of Bonded Composite Specimens Under T-Pull and Side-Bend Loadings Using Integrated Discrete-Continuum Damage Models

This paper presents the results of the authors’ contribution to the Five Eyes Science and Technology (FVEY S&T) blind prediction challenge on failure analysis of bonded composite structures under static loading. A three-dimensional finite element model was developed using integrated discrete and continuum damage modeling techniques to predict the progressive failure of IM7/5320-1 composite parts bonded with FM 309-1M adhesive under T-pull and side-bend loading conditions. To predict intralaminar failure modes—such as fiber breakage, splitting, kinking, and matrix cracking—the enhanced LaRC05 failure criteria were employed. Cohesive zone modeling was used to simulate delamination and adhesive cohesion failure. Additionally, intralaminar cohesive elements aligned with the fiber orientation were implemented to capture the interactions between delamination and matrix cracking, as well as the potential peeling of the skin near the bonded C-channel. T-pull and side-bend simulations were conducted on intact specimens and on specimens containing tip and throat defects in the bonded region. The model was used to predict ultimate strength, effective stiffness, and damage mechanisms for each loading case. Model assessment in the competition is conducted in two phases: (1) a blind prediction phase and (2) a calibration phase, against experimental force-displacement data and ultrasonic test results. In the blind prediction phase, it was predicted that in T-pull specimens, the main failure modes were cohesion failure and peeling of the first layer of the skin laminate near the Skin/Spar interface. In all side-bend loading models, the dominant failure mode was debonding of the C-channel and the noodle nested in the space between C-channels and the spar of the bonded joint. These predictions were in agreement with the experimental observations.