Research On The Multi-field Coupling Performance And Application Of The Intelligent Shear Stiffening Composites

Shear stiffening gel(SSG)is a kind of novel smart material based on polyborosilazane.Its mechanical properties are heavily dependent on the external stimulus.As a plastic and flowable material,the storage modulus of SSG is low when there is no external stimulus,but its damping factor is high.When the deformation strain rate exceeds a critical value,the storage modulus can achieve a sharp increase by several orders of magnitude.At the same time,the damping factor falls very fast.It has been proved that there is a phase transformation process in the SSG material,which changes from the viscous state into rubbery state.Due to the instantaneity and reversibility of the phase transformation,the SSG materials have great potential as a promising material in the application for functional composites and engineering structures.By now,most researches on the SSG material are focused on the application as a function material.Few attention is paid to the mechanical and electrical behaviors of SSG.There are still many challenges for the application of SSG in engineering structure design.In this work,the influence of carbon nanotubes(CNTs)and carbonyl iron particles(CIPs)on the thermodynamics and magneto-rheology behaviors of SSG was studied.A novel sensor material with dual responses to strain and magnetic field was prepared based on the conductive SSG.The effect of strain rate on sensing capacities was analyzed by compressive tests.And a phenomenological model of the sensing capacities was proposed in consideration of the rate-dependent characteristic.Then,the application of SSG in bio-inspired staggered structure with suture geometry was carried out.The mechanical and electrical responses under different impact velocities were tested via a drop weight machine.The equivalent stiffness,ratio of energy absorption,and force transmissibility during the impact process were discussed.Based on the finite element methods,the deformation process and evolution of stress state during the impact were simulated.The forced vibration behaviors of sandwich beams with suture interface were conducted.Detailed information is as follows.1.The characterization and model of SSG composites under different temperature and magnetic field.CNTs and CIPs were uniformly mixed into SSG matrix to prepare different kinds of intelligent shear stiffening composites.The strain rate,temperature and magnetic field exerted great influence on the mechanical properties of intelligent shear stiffening composites.According to the experiment results of shear stiffening composites under different temperatures and external magnetic fields,a constitutive model based on fractional derivative method was proposed.By using the time temperature superposition theory,the magneto-rheological behaviors of shear stiffening composites were analyzed under different termperature and strain rates.The fitting between theoretical model and experimental results was very good.2.The preparation and magnetic-mechanical-electrical coupling performance of CNT-CIP-SSG.The electrical conductivity and magnetic sensing capacities of shear stiffening composites were studied.The mechanical and electrical coupling behavior of the materials under different magnetic field excitation was analyzed,and the material component of CNTs and CIPs was optimized.To confirm the sensing capacities under different strain rate,compressive testing with medium rate and low-velocity impact were conducted.It showed that the conductive SSG had remarkable nonlinear electrical response under deformation.With the presence of magnetic field,the stability of the electrical-mechanical response was enhanced.The rate dependence of pressure-sensitive coefficient of SSG with magnetic flux density of 0.3 T was discussed.A phenomenological constitutive model concerning about strain rate and sensitivity coefficient was established.3.The impact-resistance capacity of sutural interfaces with SSG core.Different types of suture composites with SSG core were prepared via 3D printing technology.Through the quasi-static compression experiment under different loading rate,the results showed that the structural stiffness was highly dependent on the geometric parameters of the sutural interface.Moreover,it was found that the sutural interface could effectively suppress vibration and reduce the force transmissibility during the low-speed impact test.By introducing the conductive SSG,the deformation of sutural composites could be monitored according to the electrical responses under different loading conditions.The deformation behavior of sutural composites was simulated by finite element methods.The propagation paths of stress and strain along the sutural interface were analyzed.The enhancement mechanism to improve contact stiffness and reduce force transmissibility by sutural interface was illustrated.4.The vibration behaviors of cantilever beam with sutural structure.Sutural cantilever beams with different geometric parameters were prepared.The stiffness and toughness of cantilever beam were tested via three-point bending experiments.When the sutural angle was 45°,the structure achieved the highest stiffness.Meanwhile,the dynamic stiffness and damping factors were dependent on the suture interface angles.Then,the forced vibration experiments of the sutural cantilever beams were conducted.It was found that the resonance points shifted to lower frequency region with the presence of sutural interface.The vibration transmissibility was significantly reduced compared to conventional sandwich cantilever beams.The vibration behaviors were also influenced by the amplitudes of vibration sources and external magnetic field.The increase of external magnetic field strength could lead to better vibration suppression by suture structures.