Abstract:

Objective In view of the problems of many layers and poor flexibility of stab equipment in the current market, a bionic scale-like knitted fabric (SLKF) similar to pangolin's overlapping scale structure was knitted from ultra high molecular weight polyethylene (UHMWPE) yarns by using flat knitting technology, overcoming the difficulty of knitting complex structure with high-performance yarn. This novel fabric with overlapping scale structure is expected to further improve the stab-resistance.

Method The forming principle of SLKF was explored through simulation of fabric structure. Through quasi-static stab experiments (Fig. 4), the influences of different puncture positions, directions, scale sizes and puncture tools on the stab-resistance of the SLKF were studied. Through the structure model of a single scale and the change of fabric parameters, the rules of scale area coverage, fabric weight and scale deflection angle changing with the scale size are further clarified. The damage morphology of the SLKF was observed by optical microscope and scanning electron microscope, and the damage mechanism of the SLKF was analyzed.

Results Inspired by the overlapping structure of pangolin (Fig. 1), nine SLKFs were knitted(Fig.2), and the fabric exhibits excellent forming capabilities during the knitting process. Through simulation of the fabric structure, shrinkage of the adjacent loops in the fabric was utilized to form the overlap scale effect (Fig. 3). When stabbing in the overlapping section, or in the 0° direction, the SLKF demonstrated better stab-resistance, mainly by virtue of the large number of coils at the stab edge (Fig. 5). The stab-resistance of nine distinct SLKFs was investigated (Fig. 6), and the findings reveal a positive correlation between scale size and stab-resistance, indicating that larger scales offer enhanced protection. In order to further study the influence of scale size on stab-resistance, structure model of single scale and changes of fabric parameters was explored (Fig. 7), the results showed that the coverage of the total scale area was increased with the increase of the number of rows, the weight of fabric increased linearly with the increase of the number of rows, and the deflection angle of scales decreased gradually with the increase of the number of longitudinal rows. Two different standard knives D1 and D3 were adopted to explore the stab-resistance of SLKF, and the stabbing speed is 10 mm/min. The results demonstrate that the stab-resistance of SLKF under knife D3 is better than that of D1 (Fig. 8), and the reasons for this phenomenon can be explained as follows: under D1, the fabric failure was mainly caused by yarn cutting and tensile, accompanied by yarn extraction; and under D3, the main reasons for fabric failure were mainly extrusion and stretching, accompanied by a small amount of yarn tensile fracture failure(Fig. 9).

Conclusion In this research, inspired by the overlapping scales structure of pangolin, a bionic SLKF is prepared by UHMWPE yarn, and its forming principle and stab-resistance are discussed. The research shows that the shrinkage of the loops at the scale joint and the separate knitting of the front and back needle beds are the main principles for the formation of SLKFs. Overlapping effect of scales can effectively improve the stab-resistance of the fabric. The stabbing process of the SLKF under the two knives is different, and its damage behavior mainly includes yarn cutting fracture failure and tensile fracture failure. This work can provide reference for the preparation of stab-resistant materials.

Key words: flat knitting technology, bionic structure, scale-like knitted fabric, quasi-static stabbing, stab-resistance, damage mechanism