In this paper, an experimental and numerical study on the energy absorption characteristics due to the low-velocity impact of the composites reinforced by the multiaxial warp knitted (MWK) structures with double loop pillar stitch and common tricot stitch are presented. The influences of the MWK structural parameters on the impact behavior and energy absorption properties are discussed. A good agreement between the experimental results and simulation is obtained.

An improved MWK structure with a double loop pillar stitch is presented in this work. Its structural features, knitting process, and mechanical properties are analyzed and compared with a common tricot MWK structure. The results show that the improved MWK structure with the double loop pillar stitch has better mechanical properties than the common MWK structure with the tricot stitch.One current trend in textile structural composites is to extend their applications from secondary nonload-bearing structures to primary load-bearing structures. This requires a significant improvement in their damage tolerance and reliability. For thin to medium thickness structures, an attractive family of textile preforms, multiaxial warp knitted (MWK) structures, has the potential to meet the demand for structural composites. All layers of the insertion yarns in an MWK structure are placed in a perfect order and reveal the uniformity of the noncrimped parallel yarns [2]. While the insertion yarns play a principal role in plane reinforcement, the stitch yarns provide through-thickness reinforcement, thus significantly increasing the damage tolerance, structural integrity, and out-of-plane strength of the reinforced structure. MWK structures can be produced in a single knitting process. In addition to good ease of handling and production economics, MWK structures also conform to complex shapes, are flexible in the principal yarn directions, and have improved through-thickness strength. The mechanical properties of MWK structural composites, especially out-of-plane strength and impact behavior, could be superior to conventional woven laminated composites due to elimination of fiber crimp in the insertion yarns and the presence of the through-thickness reinforcing stitch loops [1][2][3][4][5].As illustrated in Figure 1, the commonly used basic stitches for MWK structures are the chain stitch and tricot stitch [2]. In such structures, the underlaps of the basic loops form only diagonal lines or vertical lines on the fabric plane. Consequently, the binding effects are not ideal. For better binding effects, we develop an improved MWK structure with a double loop pillar stitch in this work, and we present its structural features, knitting process, and mechanical properties and compare it with common tricot MWK structure as well.