Yarn Pull-out Test For Studying The Impact Deformation Of Fabric

Aramid fabric is used in the design of body armor for its light weight high specific strength,good impact resistance and so on.In the high-speed impact,the deformation of the fabric,yarn umcirmping and pull-out,friction between yarns,energy absorption and dissipation and other macroscopic response is extremely complex.The traditional impact experiment can only study the impact mechanics performance of the fabric in the view of macroscopic point,and it can’t investigate the deformation process of the fabric under the impact.In this paper,the process of fabric impact was modeled as the process of pulling yarns out of the fabric.The deformation process of the yarn and the energy absorption mechanism were analyzed combined with the digital marker recognition method.Firstly,the singe warp and weft yarn tensile tests were performed.The results show that the elastic modulus of the yarn is much lower than that of the single fiber,and the elastic modulus and tensile strength of the warp are slightly smaller than that of the weft.Secondly,the single yarn pull-out test was performed.The results show that the process of yarn pull-out can be divided into a static friction stage and a dynamic friction stage.In the static friction stage,the whole fabric had a large shear deformation,at the same time,the pulled yarn produced an uncrimping extension.The dynamic friction stage came when the tensile force reached the maximum value.The crimping exchange,adhesion-slip,energy absorption and dissipation were mainly produced during this stage.Thirdly,the deformation mechanism of the warp yarn pull-out was studied by the digital marker recognition method.The results show that the yarns of different rows have a similar displacement-time curve and a shear angle-time curve.In the static friction stage,the overall shear deformation of the fabric increased rapidly,and the shear deformation of the fabric came to its maximum at the maximum static friction moment.In the dynamic friction stage,the shear deformation decreased gradually,but the fabric still maintained a large overall shear deformation after the pulled yarn was completely pulled out.Fourthly,the influences of different wave number on the force and deformation behavior of fabric were studied.The force-displacement curve shows that the maximum tensile force and maximum shear angle increase with the increase of wave number,regardless the pulled yarn is the warp or the weft.When the warp yarn was pulled out,the maximum pulling force was more sensitive to the wave number.The maximum shear angle is more sensitive to warp yarn which is crimper.When the wave number is same,the warp specimens has greater shear angle compared with the weft specimens,which means the warp direction shear deformation is greater than weft during impact.At last,the finite element numerical simulation of single yarn pull-out was carried out.The results are in good agreement with the experimental results.The results show that the deformation of the pulled yarn was gradually extended from the drawing end to the end,and the umcrimping of the yarn was different at different part of the yarn.The closer to the pulled point,the greater the umcrimping was,and the stress distribution was the same to the yarn deformation.The simulations are helpful to study the uncrimping and stress translation mechanism,and it can provide a reference for further analysis of the impact mechanical properties of the fabric.