Yarn Along The Cross-section Of The Anti-cutting Performance

With the frequent occurrence of terroristic affairs in recent years, the sense of security and personal protection is increasing continuously, thus leading to the rapid development of body armoring materials, among which the development and investigation of stab-resistant and cut-resistant products are receiving more and more attention. According to the literature, there still have been no certain theories at present about the study of cut-resistant properties and cut-resistant mechanism of yarns. Although the axial tensile properties of a yarn can be taken as criterion to evaluate its cut-resistant properties, it is still not the unique one. For example, the carbon fiber bears excellent axial tensile properties, but shows evidently weak cut-resistant properties. Based on this analysis, this thesis studied the cut-resistant properties along the yarn's cross-section in detail for the first time, analyzed the influence of axial tensile properties on the cut-resistant properties of a yarn, and the research results can provide theoretical basis for design of cut-resistant yarns and prediction of the cut-resistant properties.In order to study the cut-resistant properties, a wide range of yarn samples were prepared, including 2D braided yarns with different raw materials and different structures, filament yarns with different raw materials, staple yarns with different twists and folded yarns. A special set of cut device was particularly designed for measuring the yarn's cut-resistant properties, which can be connected to any kind of drawing machines and thus can output the curve of cut force versus cut displacement, the broken cut-resistant strength, the initial cut-resistant modulus, cutting work, and so on. Based on these parameters, the yarn's cut-resistant properties can be characterized.Using this device, the thesis studied in detail the cut-resistant properties along the cross-section of yarns with different fiber materials and the influence of different yarn structures (including 2D braided covered yarn, folded yarn, filaments, staple yarn and yarns with different twists) on the cut-resistant properties, and put forward the points of view of 'area-based theory' and 'dynamic-response-based theory'. The 'area-based theory' states that the cut-resistant properties of a yarn improves with the increase of the total area of fibers' cross-sections, and the 'dynamic-response-based theory' states that when designing a cut-resistant yarn, for example, 2D braided covered yarn, the yarn with higher initial cut-resistant modulus should be used for the outer wrappedlayer and the yarn with higher broken cut-resistant strength should be used for the core. The experimental results meet these two points of view very well. And it was also found that the polyamide filament fiber yarns, high-performance polyethylene fiber yarns and polyamide staple yarns bear outstanding both cut-resistant properties and tensile properties, which can be used as preferred cut-resistant yarns;generally speaking, the yarns being twisted or folded can improve the broken cut-resistant strength, but make the initial cut-resistant modulus decrease;the 2D braided covered yarn bears excellent cut-resistant properties along the cross-section, especially when the outer layer material and the core are selected properly.In addition, this thesis studied the yarn's axial tensile properties influencing the cut-resistant properties, and investigated the yarn's tensile properties under crimped state for the first time, which is closely related to the actual state of yarns in a stab-resistant fabric during the stabbing process. A two-roller drawing devise was designed for tensile testing of a yarn under crimped state. The research results show that the tensile strength under crimped state is lower than that of straight state because during the drawing process of a yarn under crimped state, an extra force along the yarn's cross-section is exerted and thus the breaking mechanism changes. The experimental results, investigating methods and the deduced conclusions are very important references for study and characterization of the yarn's cut-resistant properties, and can provide theoretical basis for design of cut-resistant yarns and prediction of the cut-resistant properties. '...