Polarization Response Characteristics Of BST And Particle-doped PDMS Films Under Impact Loading

With the booming development of microelectromechanical systems(MEMS)technology,the force-electric conversion performance of sensors is becoming more and more important.Flexoelectric materials are a new type of force-electric coupling materials with broad prospects in weaponry,medical devices,and aerospace fields due to breaking the centrosymmetry of materials.The polymer thin film material has better flexibility and large deformation capability,which provides a solution for the selection of sensor materials under impact conditions.However,the flexoelectric coefficient of polymer thin film materials is generally low,and the existence of this barrier has become a bottleneck limiting the flexoelectric application of polymer thin film materials.Barium strontium titanate(BST)material with excellent force-electric response characteristics,prepared with polymer-like material polydimethylsiloxane(PDMS)into a composite material provides a possibility for a wide range of applications of impact polarization response.Taking BST and BST particles doped with PDMS as the research object,this paper adopts the method of combining experimental research,theoretical analysis and numerical simulation to study the impact polarization response law of unpolarized BST and BST particles doped with PDMS under impact load,and reveals the basic correlation law of material ratio,geometric parameters,dynamic mechanical properties and polarization voltage.The flexoelectric coefficients of unpolarized BST and BST particles doped PDMS in each direction were determined.The main work and achievements of this paper are as follows:(1)BST/PDMS composite specimens with different mass fractions and ratios were prepared by stirring,curing and demoulding steps.The quasi-static compression experiments of unpolarized BST blocks,BST pellets and BST/PDMS composite specimens were carried out by using a universal testing machine to obtain the quasi-static compression mechanical properties of unpolarized BST blocks,BST pellets,and BST/PDMS composite specimens.(2)The impact polarization experiments of unpolarized BST specimens with different thicknesses and ratios under different loading conditions were carried out using the separated Hopkinson pressure bar experimental system(SHPB)to combine the dynamic mechanical signals with the polarization voltage signals to clarify the forceelectric coupling response characteristics of unpolarized BST under impact loading.The results show that the dynamic mechanical characteristics of Ba0.75Sr0.25TiO3 specimens and Ba0.25Sr0.75TiO3 specimens under the same working conditions are basically the same,and the polarization voltage values of Ba0.75Sr0.25TiO3 specimens are higher than those of Ba0.25Sr0.75TiO3 specimens.(3)The impact polarization experiments of BST/PDMS composite specimens with different ratios and mass fractions at different loading rates were carried out by SHPB experimental system,and the force-electric coupling models of BST/PDMS composites from macroscopic to equivalent microscopic was established by combining the experimental data with COMSOL Multiphysics finite element analysis software.The polarization voltage distribution and flexoelectric coefficient of BST/PDMS composite specimens with different ratios and mass fractions were obtained,and the polarization response mechanism of BST/PDMS composites was clarified.The results show that the polarization voltage of BST/PDMS composite specimens is mainly related to the strain gradients in directions (?)εzz/(?)xz,(?)εxx/(?)xz and (?)εxz/(?)xx,and is provided by doped BST particles.The coefficients in the three strain gradients are generally in the order of 10-8～10-10C/m.(4)The finite element software COMSOL Multiphysics was used to numerically simulate the impact deformation process of BST,and the main strain gradient direction of BST deformation was defined.Based on the wave equation theory,the analytical solution of the one-dimensional stress wave propagation equation of BST under the impact load was calculated.The axial strain gradient and flexoelectric coefficient of BST under impact load are obtained.Finally,combining theoretical calculation and numerical simulation,the influencing factors of BST impact strain gradient and flexoelectric polarization characteristics are analyzed comprehensively.The results show that the strain gradient and impact polarization response are affected by the elastic modulus,density,and thickness of the specimen.