| Magnetoelectric(ME)composites are widely used in the manufacture of multifunctional devices because of their excellent performance such as high energy conversion efficiency and fast response speed,and they have been widely concerned by researchers in the fields of mechanics,physics,materials science and so on.However,the practical application of ME composites will be affected by many factors,such as the size of the structure,the interface of the two-phase materials,the orientation magnetic field,the structural configuration and so on.The lack of accurate performance characterization will seriously affect the usability of the composites,the range of application,and the accuracy of its structure.Therefore,this paper will consider various influencing factors by systematically and deeply studying the bending behavior of layered ME nanostructures and ME effects of polymer ME composites.Firstly,based on Kirchhoff’s thin plate theory,the influence of surface and interface effects on the bending behavior of ME nanostructures is considered.Combining the nonlinear constitutive relationship of magnetostrictive materials and the linear constitutive relationship of piezoelectric materials,a bending model of layered ME circular nanostructures with surface and interface effects was established.The governing equations for the static bending of such layered nanostructures are derived,and analytical expressions of deflection under uniform magnetic field and external load are obtained.The influence of magnetic field,structure size,electric potential and magnetic potential on the deflection of layered ME circular structure are studied as well.Then,for magnetostrictive composites with chain-arranged distribution,based on the meso-mechanics theory of the composites,an analytical expression of the effective properties is obtained through a two-step homogenization process.On this basis,a theoretical model of nonlinear magneto-mechanical-electrical coupling characteristics of polymer-based hybrid ME composites is established by combing elastic mechanics method with the constitutive equations,kinematic equations and boundary conditions of piezoelectric materials.The ME voltage coefficients of the composites with considering the oriented magnetic field or without considering the oriented magnetic field are calculated,and the theoretical calculation results are compared with software calculation results and experimental data.Then,the influence of the properties of the interface,the aspect ratio and volume fraction of the ellipsoidal inclusions,the magnetic field and the frequency on the ME voltage coefficient are further studied.Finally,the piezoelectric effects and ME effects of PVDF-based ME composites is studied.Firstly,a crystal phase transition model of graphene/PVDF piezoelectric composites is established to reveal the effect of graphene addition on the piezoelectric properties of the composites.And studies the effects of the volume fraction of β phase,the volume fraction and aspect ratio of graphene,the number of molecules and temperature on the piezoelectric coefficient of the composites,and those calculated results are compared with a series of experimental data.Then,the above model is extended to the piezoelectric properties of PVDF-based ME composites,and a theoretical model of the nonlinear ME effect of PVDF-based ME composites is established by combining the two-step homogenization process and the elastic mechanics analysis method.The ME coefficients of the composites with random and chain distribution of inclusions are calculated respectively,and the electro-mechanical,magneto-mechanical and magneto-mechanical-electrical coupling properties of the composites are further studied.The above studies make up for the deficiency of theoretical research on 2-2,0-3-2 and 0-3 type ME composites.The results in this paper can provide a solid theoretical foundation for the existing experimental research,provide suggestions and references for the optimization design and application of ME composites. |
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