Yarn Pull-out Test For Studying The Impact Of Sewing Method And Pre-tension On The Fabric

Kevlar fabric developed by the DuPont company in the United States has been widely used in the fields of bulletproof clothing manufacturing and composite toughening because of its light quality,high strength and strong corrosion resistance.The impact damage of fabric is closely related to yarn modulus,friction coefficient and shear deformation.After introduction the model experiment method and the finite element theory simulation,in this paper,the single yarn drawing test was carried out on different pre-tension and sewing methods.The deformation mechanism was discussed according to the pulling force,shear deformation,energy dissipation.The experimental results were verified by finite element simulation.The related contents are as follows:Firstly,the single yarn pullout tests of plain woven fabric under different preloads were carried out.The experiment shows that the different pretensions have no significant influence on the trend of force-displacement curve.The yarn drawing process has experienced two stages,namely,the static friction and the dynamic friction phases.The pullout force first rises linearly and then downwards in oscillating mode.The preload increases the maximum pulling force,strengthens the energy absorption capacity of the fabric and inhibits the deformation of weft yarn.Secondly,the single yarn pullout tests of sewing fabric under different preloads were conducted.The results show that the two stages of the static and the dynamic friction have been seen.The greater preload augments the maximum pulling force of the sewing fabric.The tensile test of different sewing methods under the same pretension shows that the strength of the fabric is improved by the unidirectional and bidirectional sewing methods,yet the resistance ability to the deformation in the dynamic friction phase is weakened.Thirdly,the yarn pullout tests of sewing fabric at different crossing points have been completed.Experiments show that the increase of crossing points improves the drawing resistance of the fabric,the total area between the drawing warp and the contacting wefts expands,and the drawing process becomes longer.The enhanced effect of unidirectional sewing is less than that of bidirectional sewing,and does not demonstrate a proportional relationship with the intersection points.Fourthly,the shear deformation of fabric in the yarn pullout process was studied using digital image correlation technology.The pretension and sewing do not change the basic deforming mechanism of the fabric.The less the distance to the drawing end,the greater the deformation of the wefts,the closer markers undergo the larger displacements.Partial deformation of weft after drawing is recovered,the residual deformation becomes larger while it is closer to the drawing end.Finally,the finite element numerical simulations of yarn pullouts on pretension and different dimensions were carried out.The results show that the numerical simulation agrees well with the experimental results.The pretension is mainly shared by the weft yarn adjusted by the configuration.The size effect does not affect the pullout process.The shear deformation firstly becomes larger and then falls to a fixed value.The drawing process is mainly dissipated by the friction effect,and the strain energy wave reduction is related to the geometric configuration of the fabric.The finite element simulation helps to understand the process of yarn stress and strain change,and provides a reference for further study of yarn failure mechanism and fabric deformation performance.