Lizhi Xu

In this study, bamboo fiber bundles were directly extracted from raw bamboo material to fabricate reconstituted bamboo using the traditional hot-pressing method. The tensile behaviors and failure mechanisms of both the bamboo fiber bundle and its bamboo scrimber under various strain rates (quasi-static, 350/s, 950/s and 1700/s) were investigated by the SHTB system (split-Hopkinson tensile bar, high-speed camera and digital image correlation method). The results showed that the bamboo scrimber exhibited an obvious positive strain rate effect. The ultimate tensile strength of the bamboo scrimber at a strain rate of 1700/s was close to 200 MPa, but it was only about 80 MPa under quasi-static loading. This experimental result was further validated by the tensile behaviors of single bamboo fiber bundles at different strain rates (quasi-static, 300/s, 700/s and 1500/s). In addition, as the strain rate increased, the fracture surface of the bamboo changed from a linear shape to a discontinuous folded shape.

One of the ways to improve the protection ability of bulletproof vests is to optimize flexible fabrics. Therefore, understanding the energy absorption law of fabrics and exploring better protection structures is important. Taking aramid (Kevlar®29) plain woven fabric (areal density 90 g/m ² ) and ultra-high-molecular-weight polyethylene (UHMWPE) unidirectional (UD) fabric (areal density 120 g/m ² ) as research objects, two types of single-material target plates and three types of two-material composite target plates are studied through ballistic tests. Five types of target plates are impacted by 8-mm steel balls at 200 m/s to analyze their energy absorption laws and failure modes. Research shows that due to the loose structure of UD cloth and less energy absorption. Under three areal density conditions of 360 g/m ² , 720 g/m ² , and 1080 g/m ² , the energy absorbed by a single plain weave fabric target plate is 46.77%, 35.49%, and 30.07% higher than that of a single UD fabric target plate, respectively. In composite target plates, the target plate with plain weave fabric in front and UD fabric at the back has stronger protection than the reversed one, but is weaker than a single plain weave fabric target plate at the same areal density. At 720 g/m ² areal density, the energy absorption of the three is 24.31 J, 22.83 J, and 30.68 J, respectively. The new hybrid composite fabric target (alternating layers of plain weave fabric and UD fabric) absorbs 33.46 J at 720 g/m ² surface density. Due to the maximum damage degree of Kevlar fabric and UD fabric, the target plate shows the best protection effect.

This paper studies the influence of the weave parameter on the ballistic performance of multi-ply systems. Three types of plain weaves were put into investigation, namely, A090, A200, and A400. Tensile and yarn pull-out tests were performed to investigate the responses of fabric upon quasi-static loading. Penetration tests were performed to characterize the energy absorption capability of different multi-ply systems at impacting velocities ranging from 250 m/s to 460 m/s. It was found that the strength of the fabric sample increased almost linearly with fabric areal density, and the coarser weaves exhibited a greater resistance against yarn pull-out. The ballistic limit ( V₅₀) of finer weave 13A9, is around than 42.5% higher than coarser weave 3A4. In terms of hybrid systems, placing finer fabrics in front and coarser fabrics in the rear exhibits higher ballistic limits than the reversed sequence (8–20 m/s differences), while placing coarser fabrics in front exhibited greater energy absorption capability when the impact velocity is sufficient to cause instant and localized failure. It was also found that the ballistic performance of the hybrid systems does not alter significantly with the mass percentage of the coarser weaves at high impact velocities (greater than 400 m/s). The results indicate that replacing the expensive ballistic weaves with cheap materials in a hybrid system is a reasonable alternative to achieve cost reduction without significant performance degradation.