Assessment of low-velocity impact response of a hybrid carbon-aramid braided composite by algorithmic quantification of volumetric structures

This work investigates the impact response of a hybrid two-dimensional (2D) tubular braided composite through ex-situ examination of its internal structure. An inter-ply hybrid laminate of biaxial braided carbon and aramid layers was manufactured using hand lay-up. The sample underwent split Hopkinson pressure bar (SHPB) impact testing, where the applied energy induced barely visible impact damage (BVID). Volumetric representations of the sample were created before and after impact testing through X-ray imaging using micro-computed tomography (µCT). In this work, algorithms were developed based on image processing techniques to extract and register voids for individual analysis, and detect impact cracks in the damaged sample. Statistical analyses in the form of paired-sample t-tests were performed for void properties and overall surface topologies. Additionally, measurement of 3D deformation within selected regions of the sample was performed using digital volume correlation (DVC). Results showed that the impact damage did not cause significant void enlargement, but instead caused surface topology shifts, particularly at the inner surface, owing to plastic deformations caused by impact cracks, which were primarily caused by delamination and developed from large voids at the site of impact. The hybrid material configuration exhibited a phenomenon where the inner and outer layers minimized cracking in the middle layer, causing plastic deformation to be the primary impact response of the middle layer.