Study On The Performance Control And Toughening Design Of Shear Stiffening Materials

Shear stiffening gel(SSG)is a kind of polyborosiloxane smart material.Based on the unique"Boron-Oxygen" dynamic crosslinking,the mechanical behavior of shear stiffening gel displays an obvious strain rate-dependent effect.In the natural state,the shear stiffening gel shows a viscous colloidal state with a low storage modulus.With the increment of external strain rates,the storage modulus of the shear stiffening gel dramatically increases,and the shear stiffening gel transforms into a rubbery state or even a glassy state.Based on the adaptive strain-rate stiffening effect as well as the rapid and reversible mechanical response of shear stiffening gel,the shear stiffening gel has attracted strong attention in the fields of vibration isolation,flexible protection,and intelligent sensing in recent years.However,the research on shear stiffening gel is still somewhat in its infancy.For example,the studies closely related to engineering applications,such as the functional modification of shear stiffening gel and the toughening design of shear stiffening composites,still need to be further investigated.Herein,aiming at the engineering application of shear stiffening materials,a series of researches on basic scientific problems have been carried out.Based on the functional modification of shear stiffening gel,a high-performance fabric composite with an interesting mechano-electric coupling effect is fabricated by combining the conductive shear stiffening gel with Kevlar fabric.The fabric composite not only shows a remarkable antiimpact property under the ballistic impact loadings but also achieves self-perception ability to external impact strength according to the variation of the resistance values.Utilizing the interpenetrating polymer network method,a new type of shear stiffening elastomer(SSE)with a stable geometry in the natural state is fabricated by intersecting shear stiffening gel with methyl vinyl silicone rubber(VMQ).On this basis,the strain rate-dependent mechanical behavior of shear stiffening elastomer is systematically characterized,and its application as an active impact material in the field of low lethality flexible bullets is explored.To solve the problem of limited toughness in traditional shear stiffening systems,the toughening method based on macroscopic "soft-hard"phase elastomer and the "solid-liquid coupling"mechanism of liquid metal inclusions are utilized to design novel shear stiffening composites with the improved anti-crack property.On this basis,the toughening mechanisms of the two methods are deeply explored.The specific work includes the following aspects:1.Study on the anti-impact performance and mechano-electrical coupling behavior for the conductive shear stiffening fabrics composites.The conductive shear stiffening gel is fabricated by introducing functional carbon black particles into the shear stiffening gel matrix.Using a "solution blending and drying molding" method,the conductive shear stiffening gel is evenly dispersed in the Kevlar fabric.Based on the rheological characterization and yarns pull-out testing,the effect of conductive shear stiffening gel on improving the mechanical behavior of Kevlar fabric is explored.The low-velocity drop-tower impact experimental system and highvelocity ballistic impact experimental platform are built to discuss the influence of carbon black and shear st iffening gel content on the anti-impact performance of the fabric composite.Using the composite with the optimal ratio,the mechano-electric coupling effect under different forms of impact loadings is studied.On this basis,a protective helmet with in-situ dynamic sensing ability is designed using the high-performance conductive shear stiffening fabric composite.2.Study on the preparation and application of shear stiffening elastomer based on the interpenetrating polymer network method.Based on the interpenetrating polymer network method,the mixture of shear stiffening gel and methyl vinyl silicone rubber is vulcanized under high temperature and pressure to prepare a novel shear stiffening elastomer(SSE).The shear stiffening elastomer possesses a stable geometry in the natural state,which effectively overcomes the cold flow drawback of the traditional shear stiffening gel.The shear stiffening elastomer is prepared as a sphere impactor and its dynamic response as an active impact material is investigated through free fall impact testing against a rigid plane and a high-velocity impact against a polycarbonate(PC)plate.Besides,the phase transition behavior of shear stiffening elastomer under different strain rates is further explained using the finite element analysis method.Based on the characterization of the dynamic process of shear stiffening elastomer impacting against ballistic gelatin at different initial velocities,the feasibility of shear stiffening elastomer as a lowlethality flexible bullet is verified.3.Study on toughening design and mechanical behavior of shear stiffening elastomer based on macroscopic soft-hard phase structure.Inspired by the design strategy of macroscopic soft-hard phase elastomer,a toughened shear stiffening elastomer is fabricated by uniformly distributing viscoelastic shear stiffening elastomer ribs in the hyperelastic Ecoflex matrix.The difference in mechanical behavior between the soft-phase Ecoflex and hard-phase shear stiffening elastomer is characterized by uniaxial tensile testing.Meanwhile,the interfacial bonding property on the interface of Ecoflex and shear stiffening elastomer is verified through the T-peeling testing.The mechanical response and morphology evolution of notched composite and homogeneous Ecoflex during the crack propagation testing are compared under different strain rates.It is demonstrated that the existence of shear stiffening elastomer ribs can effectively improve the anticrack ability of the soft-hard phase composite.Besides,using the finite element analysis method,the toughening mechanism of the composite is further explained.4.Study on toughening design and basic applications of shear stiffening composite based on "solid-liquid coupling" mechanism of liquid metal inclusion.Using a blending process,a multifunctional liquid metal-reinforced shear stiffening composite is prepared by dispersing micron liquid metal droplets into the shear stiffening elastomer matrix.Based on the uniaxial tensile test,crack propagation test,and in-situ microscopic observation technology,the toughening mechanism for the composite is clarified.The influence of liquid metal volume fraction and the type of shear stiffening matrix on the fracture strain,fracture toughness,and thermal conductivity of the composite is detailedly investigated.Besides,the drop tower impact testing,adhesive testing,and self-healing characterization are carried out to evaluate the adaptability of the composite to complex loading environments.Benefiting from the remarkable mechanical and thermal behavior,the application prospects of the liquid metal-reinforced shear stiffening composite in rapid thermal camouflage,stretchable heat-dissipation matrix,and thermo-mechanical coupling mobile phone protective shell are verified.