Characterization of mode II specimen using I-fiber Stitching process

The reinforcement of composite structures in the through-thickness direction has been developed through a new stitching process. This reinforcement is called I-fiber stitching process due to the final shape of the reinforced fiber. Following mode I results from a previous research, the present study proposes a mode II analysis in order to define the cohesive parameters through a cohesive law that will allow to predict the behavior of reinforced composite structures under this specific fracture mechanism. Several stitching patterns have been tested with two kinds of dry carbon fiber yarn stitched as reinforcement, the first group with 1 × 6 and 2 × 6 for 6 k yarn and the second group with 1 × 3 and 2 × 3 patterns for 12 k yarn. A parametric study was performed after test a single stitch unit cell specimen for the two carbon fiber yarns to obtain the cohesive parameters that have been used after in a macro-scale model with the reinforced stitching pattern. Using the finite element modeling, the numerical analyses were compared with the test results and have showed a great concordance with the experiments, these results have allowed to fix the stitching parameters through the cohesive law for mode II fracture mechanism.