Weft Knitted Fabric Stab Mechanism

Research on the materials of body armors for personal protection is in the rapid development. The threat from knives and other sharp objects exists more largely than that of gun for the prohibition of the use of guns in many countries. Therefore, stab-resistant fabrics are receiving more and more attention than ballistic fabrics. Body armors based on knitted materials have been used widely for their excellent properties such as lightweight, high price efficiency, good forming abilities etc. in many kinds of fields for personal protection which also have extentive application prospect. There have been many studies on the exploitation of stab-resistant products so far, but little theory on stab-resistant mechanism. Some tests show that weft knitted fabric made from the Kevlar or HPPE fibers possesss stab resistant properties to some extent. The purpose of this paper is to make research on the stab resistant mechanism of the weft knitted fabrics that will fill the blank of the theory at this aspect and lay a foundation for the application of weft knitted fabrics in the field of stab resistant products.A new method for measuring the transverse shear mechanical properties in the plane perpendicular to the longitudinal direction of high performance yarns is developed and applied it to high performance yarns. The shear curve of high performance yarns by means of this method can be obtained according to which the shear force and modulus can be calculated, The yarn failure mechanism and affected factors of shear properties are analysised, the effects on yarn shear properties of the shearing velocity are discussed. The research of this part con tributes to the further study of the shear properties of the high performance yarns and can work as a basis for computational model of the weft knitted fabric response to the quasistatic penetration by dagger.A structural model that characterizes friction in fibrous materials and the factors affecting friction in fibers are discussed. An experimental investigation is designed devoted to the inter-yarn friction in weft-knitted structures made of high performance fibers. The method and results of the experimental investigation are analyzed which serve as a basis for study on yarn slippage of weft knitted fabrics when being stabbed by the sharp object.The yarn slippage of the loop of the weft knitted fabric during penetration by the sharp dagger is studied through a designed quasi-static penetration test and a series of experiments. The loop model a of tight fabrics and the yarn slippage length computional model of the loop of the weft knitted fabric are derived which agree with the experimental results very well and serve as a basis for a computational model of the weft knitted fabric response to impact of thesharp dagger.Thhe evolution and mechanism of the failure of the weft knitted fabric during penetration by the sharp dagger is studied through a designed quasi-static penetration test. The stroke and load on the penetrator are recorded during the test. The two modes of fabric failure are observed in these tests-yarn slippage and yarn shearing failure, which are the same modes observed in impact tests, although the extent to which each mode occurs is different in static and dynamic tests. A computational model of the weft knitted fabric response to impact of the sharp dagger is developed. The theoretical results and the experimental ones are in good agreement.The study belongs to the scope of the international hot study, which will benefit for the further research on personal stab resistant body armors.