Impact fracture behaviors of three-dimensional braided composite U-notch beam subjected to three-point bending

Impact fracture behaviors of three-dimensional braided composites are critical to designing the braided composite parts. Here we report the impact fracture behaviors of three-dimensional braided composite U-notch beam tested on a modified split Hopkinson pressure bar. Crack mouth opening displacement, deformation process, and crack evolutions were recorded with high-speed photography camera. The digital image correlation method was used to calculate deformation contours of the braided composite. A microstructure model of the three-dimensional braided composite U-notch beam was established for analyzing damage evolution and fracture mechanisms. The histories of deformation, the load, and the crack mouth opening displacement were obtained from the impact fracture test and finite element analysis. It was found that the impact fracture resistance and morphologies were influenced by the braided structure and braided yarn orientations. The crack generated at the notch tip and then propagated along the braided angle direction rather than the perpendicular direction that often occurred for isotropic materials, such as the epoxy resin solid. The combinations of different braided angle and yarns are recommended for high impact fracture behavior design.