Impact Research And Finite Element Analysis Of Flexible Composite Materials With Non-Newtonian Fluid Lattice Structur

In the field of flexible protection,non-Newtonian fluids exhibit great potential for application,and they are commonly combined with high-performance fabrics at home and abroad to exploit their properties of high energy storage modulus and strain rate sensitivity.Compared with shear thickening fluid（STF）,shear thickening gel（SSG）overcomes the defects such as particle settling,fluid volatility and difficult storage,and is easier to combine with textile materials.Therefore,this project firstly explores the synthesis process of SSG and laminates it with Kevlar fabric of Kirigami skeleton to form a special dot matrix arrangement,and finally encapsulates it by foaming to form a class of flexible cushioning composites with both negative Poisson’s ratio effect and excellent impact resistance.The boric acid,silicon dioxide,and hydroxy silicone oil were used as main raw materials to manufacture SSG.The prepared SSG was analyzed by infrared,thermal weight loss,and rheological properties,and the effect of raw material ratio and synthesis temperature on rheological properties of SSG was investigated.Studies have shown that the overall loss factor of all samples is in the range of 10^-1 to 10¹.The ratio of reaction temperature and raw materials has a greater influence on the rheology of SSG.The higher the reaction temperature and the content of silica and boric acid in the reactants,the higher the overall dynamic storage modulus of SSG,with the highest storage modulus reaching 2.53 Mpa.The SSG/Kevlar composite were manufactured by coating process.The low velocity impact experiment exhibits that all SSG samples have an enhanced effect on neat fabric.The peak load of T280 is the highest,reaching 318.2 N,which is 249.4%higher than pure fabric,and its energy absorption ratio is 70.20%.The damage morphology shows that the wettability and stiffening properties of SSG both have a positive effect on the impact resistance.As the impact velocity and coating weight increase,energy absorption increases simultaneously,and the specific energy absorption（SEA）of the single-layer T220 composite reaches 0.50 J/g.The NPRSC（Negative Poisson’s Ratio Skeleton Composite）composite was finally prepared by preparing the coated composite into a negative Poisson’s ratio structured prepreg skeleton by the Kirigami process and foamed after the internal filling with SSG.It was shown that NPRSC has superior flexibility and lower compressive modulus than the ortho-Poisson sample with the same ratio of SSG filling,about 33.3%.In addition,the energy absorption ratio of R3/4 was greater than 70%at various impact velocities.At the penetration degree of 0.25,the Area Specific Energy Absorption（ASEA）of R3/4 was 7.75 times that of the PU&SK samples,and the Mass Specific Energy Absorption（MSEA）was 4.42 times,showing excellent impact resistance and energy absorption efficiency.In addition,this thesis analyzes the viscous-fluid/modulus ratios and Poisson’s ratio effects of the components in the impact resistance mechanism of NPRSC composites by establishing a fluid-structure interaction model of non-Newtonian fluids and large deformation materials,and shows that the fluid viscosity in the composites affects the load bearing and stress diffusion during impact.The thickening gradient of the non-Newtonian fluid can laterally disperse the impact stress,and the lower modulus PU-1 produces larger lateral deformation and further promotes the energy exchange between the fluid and solid material during impact,which improves the impact resistance.It is able to spread the force laterally,showing its unique impact resistant mechanism.