Micro-scale Modeling Of Kevlar 49 2-D Woven Fabric And Analysis Of Yarn Pull-out Behavior

Kevlar 49 fabric has the characteristics of high specific strength,heat insulation and flame retardant,and is a high-quality material that resists ballistic impact.However,due to the complex diversity of yarn spatial configuration and the high transient and high nonlinearity caused by impact loading,it has brought great challenges to this research.As the main failure mode of projectile impact fabric,yarn pull-out can observe the force process of fabric in real time under the action of pull-out load,which is an important way to study the impact performance of fabric.Existing yarn pull-out experiments failed to reveal the mechanism of stress propagation and energy conversion mechanism during the extraction process.In addition,the fabric model used in the existing simulation analysis ignores the relative movement between fibers,ideally assumes that the cross-sectional shape of the yarn stays constant,and fails to effectively solve the effect of mechanical properties such as fiber strength,stiffness and Young's modulus on the yarn pull-out performance.In view of the above problems,this thesis takes Kevlar 49 2-D woven fabric as the research object,establishes its micro-geometric structure model at the sub-yarn scale,and uses ABAQUS to analyze its mechanical properties of yarn pull-out on this basis.The main research content and results of this thesis are as follows:(1)The unit cell topology of the 3-D orthogonal weave fabric is established by the Digital Element Approach(DEA).Then,periodic boundary and constant tension are applied at yarn ends.Each yarn is discretized into a predetermined number of digital fibers.As a result,the yarn cross-section shape and its spatial configuration are changed through the dynamic weaving process simulation.The results show that when the applied tension of warp,weft,and weaver yarns is 0.3N,0.3N,and 0.02 N respectively,the thickness of the numerical model is only 6.32% less than that of the experimental one.The micro-geometry of the numerical model matches perfectly with the microscopic images.The simulation results validated the DEA in determining the micro-geometry of woven fabric at sub-yarn scale.(2)The micro-geometry of 2-D woven fabric is generated through weaving process simulation implementing the Digital Element Approach.The yarn surface is then calculated.On this basis,the pull-out behavior of single yarn is simulated by ABAQUS.One solid element is used through the thickness of the yarn and the yarn material properties are defined.Compare the simulation with the experiment,the results show that the discrepancy between the simulated peak pull-out force and the peak transverse force versus the experimental ones are 5.96% and-7.84%,respectively.The proposed model is capable of predicting the yarn pull-out performance accurately.(3)The effect of transverse pre-load and yarn-to-yarn friction on pull-out behavior and energy transfer mechanism are obtained.The results show that energy brought by the the external force is mainly dissipated through frictional energy.When the transverse pre-load increases,the growth rate of the yarn peak pull-out force gradually decreases.When the yarn-to-yarn friction coefficient increases,the growth rate of the yarn peak pull-out force gradually increases.