TTCP Blind Analysis Challenge: Simulation of T-Pull Tests using the Power Law and B-K Mixed-Mode Progressive Failure Criteria in ABAQUS

This study investigates the failure behavior of composite T-joint specimens under T-pull, Side-Bend, and Mixed-Shear loading conditions. The work was performed as part of a blind prediction challenge led by the Air Force Research Laboratory (AFRL). The primary objective of this paper is to predict damage initiation and propagation in composite C-channels bonded to a spar cap and skin, using Finite Element Analysis (FEA) and Cohesive Zone Modeling (CZM) using a commercially available FEA code in order to provide a standard benchmark for CPU time and prediction accuracy. In this paper, for the T-pull and Mixed-Shear configurations, the simulations results are presented as true blind predictions in the sense that the interface properties were derived strictly from the AFRL provided adhesive characterization data (DCB/ENF and tensile/shear strength) without prior knowledge of the test results. These blind models showed good agreement with the experimental peak loads for the T-Pull pristine and throat-defect cases, as well as for the Mixed-Shear configuration. In contrast, the Side-Bend configuration presented a unique challenge because failure initiated within the composite "noodle" region rather than the adhesive bond line. Since the interlaminar strength in this region is difficult to predict from the material data, the blind prediction initially deviated from the experimental results. To address this, a post-test calibration was performed using the experimental data from the “Tip Defect” case to accurately tune the cohesive interface strength for the noodle region. Additionally, a post-test investigation was conducted on the T-pull tip-defect case, which demonstrated that a complex "double delamination" failure mode was the primary driver for the lower peak loads observed in experiments compared with the single-interface blind prediction.