Preparation And Dynamic Mechanical Properties Of Negative Poisson’s Ratio Warp-knitted Spacer Fabric Reinforced Composite

Poisson’s ratio is defined as the negative value of the ratio of the strain perpendicular to the load direction and the strain along the load direction.The unique auxetic effect and hyperbolic effect of the negative Poisson’s ratio material make its fracture toughness,shear modulus,energy absorption,indentation resistance and other properties significantly enhanced compared with the traditional positive Poisson’s ratio material,which are widely used in protective equipment and intelligent textiles,textile composites and other fields.At the same time,the unique three-dimensional structure of the spacer fabric makes it have good air permeability,moisture permeability,sound insulation and filtration,as well as compression and shock absorption.Spacer fabrics are widely used in clothing,home textile,automobile,building covering materials,aerospace and other fields.Negative Poisson’s ratio warp knitted spacer fabric is a kind of warp knitted spacer fabric with negative Poisson’s ratio effect.The negative Poisson’s ratio warp knitted spacer fabric shows "auxetic effect" in unidirectional stretching,and has good impact resistance and energy absorption performance.Firstly,the paper uses ABAQUS/explicit module simulated the deformation and impact resistance of negative Poisson ratio warp knitted fabric.Because the loop models of negative Poisson ratio warp knitted fabric is complex,so the fabric model is simplified and use rib as smallest element to build model.The tensile and impact simulation of the fabric was carried out.The simulation results are basically consistent with the experiment results.It is found that the negative Poisson’s ratio effect and impact resistance of the fabric model are closely related to the angle θ and the ratio of the long /short rib.The auxetic effect of fabric model increase with the increase of angle θ when angle θ≥45°,it would have more obvious auxetic effect when increase the ratio of long/short rib.But it would conduct fluctuations when the ratio of long/short rib is too large.The impact resistance of the fabric model is positively related to the angle θ,but it is nothing to the ratio of the long/short rib.Secondly,the quasi-static penetration performance of negative Poisson’s ratio warp knitted spacer fabric/silicone rubber flexible composite is studied in this paper.The stab resistance experiment of flexible composite was carried out by universal material testing machine.It is found that the stab resistance property of the soft composites have a positive correlation with the negative Poisson’s ratio value of the fabric and the filling rate of the matrix.The main performance of the composite is higher peak load,higher energy absorption value,longer displacement and smaller damage.The main reason is that the fabric with the better negative Poisson’s ratio has a more compact surface structure,which can stand for higher stab force and absorb more energy.Moreover,silicone rubber can enhance the overall mechanical properties of the composite and resist more external damage.Then,shear thickening fluid with different mass fractions and different carriers were prepared by mechanical stirring.The steady-state and dynamic rheological properties of STF with different parameters were tested by rheological tester.It is found that the shear thickening fluid has obvious strain rate effect at critical shear rate.At the same time,STF with different mass fraction shows different shear thickening effect.The initial viscosity and maximum viscosity of the STF increase with the increase of the silica mass fraction,while the critical shear rate decreases with the increase of the silica content in the dispersion system.The molecular weight of PEG has no significant effect on the viscosity of the dispersion system.Dynamic rheological experiments show that the loss modulus of the STF is larger than the storage modulus when the shear rate reaches the critical shear rate,and the STF show obvious energy absorption behavior.At the same time,different parameters’ STF and different negative Poisson’s ratio effect’s warp knitted spacer fabrics are used to prepare flexible composite.The low-velocity impact test of the flexible composite is carried out by using the drop weight impact tester.The deformation process of the composite under the impact load is analyzed.The influence of different negative Poisson’s ratio effect’s warp knitted spacer fabric,different mass fractions and different carriers’ STF on composite impact resistance and energy absorption are also analyzed.It is found that the negative Poisson’s ratio effect of the reinforced fabric has a significant impact on the impact resistance of the composite.The impact peak load and energy absorption of the composite is enhanced with the increase of the negative Poisson’s ratio of the warp knitted spacer fabric.The main reason is that fabric with better negative Poisson’s ratio would have more deformable hexagonal structure unit,the longer time is required for fully expanded in the impact process,so composite can absorb higher energy.At the same time,composite would have denser impacted face when fabric with better auxetic effect,so composite would have higher impact peak load.STF is also one of the important factors that affect the impact resistance of composites.It is easier to generate coupling effect under the action of higher mass fraction STF,which makes the impact resistance of composites stronger.At the same time,it is more likely to generate shear thickening effect under the same shear rate when STF with higher silica content,so it is more beneficial to improve the impact resistance and energy absorption of composite.The molecular weight of PEG has no obvious effect on the impact resistance of the composite.At last,the impact resistance and energy absorption properties of composite reinforced with different negative Poisson ratio warp knitted spacer fabric were studied.The influences of different negative Poisson’s ratio and initial impact energy on the impact resistance of the composite were studied by displacement-load curve,time-load curve,displacement-energy absorption curve and the morphology characteristics of the composite after failure.The experimental results show that the maximum impact load and energy absorption value of the composite increase with the increase of the negative Poisson ratio of the warp knitted spacer fabric,and the damage degree of the composite is lower after the impact load.This is mainly because fabric with better auxetic effect would have more auxetic structural units,so the load peak value and energy absorption value would be higher and the damage degree would be lower.The initial impact energy would influence the increase rate of impact load,and faster the damage of the composite.In this paper,the influence of fabric’s negative Poisson’s ratio effect on the impact resistance of flexible/ rigid composites is mainly discussed.At the same time,the deformation mechanism of fabric model with negative Poisson’s ratio is simulated by finite element method,which provides theoretical guidance for the application of composite materials with negative Poisson’s ratio.