Study On Mechanical Properties Of Shear Thickening Fluid And Its Fabric Composites

Shear thickening fluid(STF)is a dense suspension consisting of micron or nanoscale particles dispersed in a polar medium.It has a sharp rise in viscosity at high shear rate,and at the same time possesses the energy dissipation characteristics of the liquid and elastic characteristics of the solid.It is a new type of smart material and has been applied to human protection,damping equipment,sports equipment and other fields,showing significant advantages and prospects.In particular,the protective clothing made of STF and high-strength fibers has a significantly higher impact resistance than neat fiber fabrics.In view of the important application background of shear thickening composites,it is urgent to carry out research on the preparation and mechanical properties of relevant practical materials.For this purpose,this article first developed the preparation method of STF.Then,the macroscopic rheological behavior measurement was combined with the evolution of microstructures to explore the intrinsic mechanism of shear thickening behavior.After that,the coating material was selected to improve the sealability of the STF in the fiber fabric and to enhance the impact resistance.Finally,the structure of the STF fabric composite was optimized.This study provided theoretical and experimental evidence for the development of new protective materials and their application in engineering practice.The specific content includes the following aspects:1.Development of STF.A variety of high-performance,stable and controllable STFs were developed and an STF based on silica particles with pore structure on the surface was studied in depth.Due to the porous structure of the particle surface,the BET specific surface area is as high as 794.50 m2/g,and the solid-liquid contact area of porous particles and solvent molecules is changed,which in turn affects the shear thickening behavior of the STF.2.Study on the rheological behavior of STF.The rheological behavior of STF based on mineral SiO2 particles was studied by characterization of rheological tests.The effects of parallel plate spacing,rotor surface roughness,and volume fraction of dispersed phase particles were investigated.The difference in rheological curves under two different control modes(shear rate and shear stress control)was compared.It was found that after controlling the shear stress to increase to the shear-thickening interval,the viscosity of the high concentration STF showed an S-shaped foldback phenomenon,and the corresponding microstructure was in a state of Newtonian flow and shear-thickening coexistence.The regularity of the change of normal force from negative value to positive value during the transition from continuous shear thickening(CST)to discontinuous shear thickening(DST)was studied.Combined with experimental results,the microscopic mechanism of shear thickening behavior was further analyzed.3.Development of STF fabric composites and its impact resistance test.Shear-stiffening gel(STG)was introduced into STF-impregnated Kevlar(?)fabric(Kevlar/STF)to develop a new type of shear thickening fabric composite(Kevlar/STF/STG).The encapsulation by STG not only improved the stability of Kevlar/STF material,but also helped STF to improve the impact resistance of neat fabric together.Yarn pull-out test,split Hopkinson pressure bar(SHPB)impact test,and rounded tip rod impact test were performed on the fabric composites.By analyzing the failure mechanism of fabric under impact,the excellent protective effect of Kevlar/STF/STG was attributed to the increase of the fiber friction caused by STF and STG,resulting in a change in the mechanism of fabric failure and driving more yarns to share the impact force.4.Structural optimization of STF fabric composites.The Kevlar/STF/STG was formed by combining STG with Kevlar/STF by "dip and dry method" and "hand layup method",and its protective ability under the impact of rounded tip rod,knife and spike was studied.The arrangement position of the components and the amount of additives on the stacking of multilayer fabrics were changed,and the impact resistance was observed to achieve structural optimization.In addition,the mechanism of impact resistance of fabrics was also discussed from the perspective of energy dissipation mode under impact.