| Kevlar 49 flexible fabric,which has the characteristics of high strength,high corrosion resistance,high energy absorption and light-weight,is widely used in the preparation of light flexible protective equipment.When plain woven fabric is subjected to impact,there will be a series of complex interactions among the yarns,including uncrimp and elongation,friction and slippage,yarn deformation,yarn fracture,etc.In the high-speed impact test of ballistic penetration,the interaction and mechanical response of the yarn in the fabric occur instantaneously at high speed.These typical mechanical phenomena are difficult to be completely measured and evaluated.Therefore,in view of the mechanical problems of the interface stress transfer and energy absorption in the impact process of plain woven aramid fabric,the high-speed ballistic penetration test is modeled as a quasi-static test method in this paper,so as to carry out theoretical analysis,measurement and evaluation more specifically for the mechanical problems of the fabric,and further develop the silicon-based shear thickener modified fabric to improve the fabric Energy absorption capacity.At first,the yarn pullout phenomenon of plain woven fabric under impact in ballistic penetration is modeled as a quasi-static pull-out test method to evaluate the energy consumption of interface friction between fabrics and yarns.Based on the experimental scheme of yarn drawing speed of 100,500,1000 mm/min and fabric transverse preload of 0,100,200 N,the yarn pullout test was carried out,and the in-plane shear deformation of the fabric was measured by digital image correlation marker point method.The linear-constant(L-C)and bilinear(L-L)stress transfer models are proposed to analyze the energy absorption mechanism during single yarn pullout.The results show that the strain energy of tensioned yarn can be ignored compared with friction energy consumption,and it is not significantly related to yarn pullout speed.It is found that the shear deformation stiffness of the fabric is directly proportional to the horizontal preload level of the fabric specimen.Secondly,according to the 3D off-plane displacement field of the clay impact basin,the impact deformation of the flexible fabric is evaluated,and a new index for evaluating the impact resistance with the impact basin volume and energy absorption rate is proposed.Through the non penetration and low-speed impact test of single-layer plain woven fabric,the limit deformation state of the fabric is recorded by the oily clay,and the three-dimensional shape of the impact pit is measured by the multi-frequency inverse-phase projection fringe method;a clay indentation test is developed to calibrate the relationship between the deformation energy and the deformation volume of the clay,and a new indicator is proposed to evaluate the impact resistance of the fabric with energy absorption efficiency.Finally,the Kevlar 49 plain weave fabric was impregnated with 62,65 and 70 wt.%silicon-based shear thickening fluid(STF)to form STF-Kevlar bi-phase composite material to enhance the energy absorption capacity of flexible fabrics.STF damping effect improvement was analyzed for friction performance between flexible fabric yarns and single-layer fabric low-speed impact performance.In order to evaluate the effect of Kevlar/STF composites on friction and energy consumption,yarn pullout test was carried out.The results show that the energy consumption of interfacial friction between yarns is significantly increased,which is related to the yarn pullout speed.The results of low speed impact test show that the STF improves the impact energy absorption capacity of the fabric,and enhances the stress transfer efficiency between the primary yarn and the secondary yarn. |
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