Dynamic Analysis And Energy Harvesting Design Of Sandwich Structure Based On Piecewise Shear Deformation Theory

Sandwich structure has properties such as high specific strength,high specific stiffness,excellent sound and heat insulation,etc.Thus,it has been widely used in ships,high-speed trains,aerospace and other engineering structures.In extreme high temperature and noise environment,the combination of thermal stress,aerodynamic noise and mechanical loading has a major impact on the aircraft structure.Therefore,studing dynamic characteristics of the sandwich structure is of significance for structural design.With the rapid development of MEMS,integrated circuit technology,and intelligent systems and structures,it is possible for energy harvesting technology to provide energy for low-power microelectronic devices and wireless sensor networks.In this dissertation,a piecewise shear deformation theory is proposed to analyze dynamic characteristics of sandwich structures,including free vibration,sound radiation,sound transmission loss,post-buckling,etc.Based on the proposed theory of piecewise shear deformation,several kinds of efficient energy harvesters are designed to harvesting energy from broadband,low-frequency and low-amplitude vibration sources.The main research contents of this dissertation are as follows:(1)Some of the existing theoretical models have low accuracy and are difficult to accurately predict the dynamic characteristics of sandwich structures.Some theoretical models are too complicated and can hardly analyze the vibro-acoustic and post-buckling characteristics of sandwich structures.In this dissertation,a simple,accurate and efficient piecewise shear deformation theory is proposed to conveniently analyze dynamic characteristics of sandwich structure such as free vibration,sound radiation,sound transmission loss and post-buckling in thermal environment.The governing equations in thermal environment are obtained based on Hamilton’s principle.For simply supported boundary condition,the analytical solution of sandwich plate is derived and the influence of temperature on the natural frequency,sound radiation and sound transmission loss is studied.(2)In general,it is difficult to obtain analytical solution of plate for clamped boundary conditions.To study dynamic characteristics such vibration and sound insulation of clamped sandwich plate,this dissertation starts from a simple composite laminated plate.The approximate analytic solution of the laminated plate is firstly obtained by assumed-mode method and Galerkin weighted residual method based on the classical laminated theory and first-order shear deformation theory.Then this modeling is extended to the sandwich plate and the approximate analytical solution of the clamped sandwich plate is obtained based on the proposed piecewise shear deformation theory.The free vibration and vibro-acoustic characteristics of clamped sandwich plate are finally studied theoretically.(3)The piecewise shear deformation theory of sandwich beam is proposed.Thermal post-buckling and free-vibration characteristics of the sandwich beam are studied theoretically,including simple supported boundary and clamped boundary conditions.The nonlinear governing equations of the sandwich beam are obtained based on the principle of virtual work.The natural frequency and buckling temperature of the sandwich beam are derived.The new equilibrium position of the sandwich beam after buckling is obtained using the nonlinear equations.The free vibration of the sandwich beam after buckling is obtained when the temperature exceeds the critical one.The influence of temperature on buckling and vibration characteristics is analyzed in detail.(4)The sandwich piezoelectric vibration energy harvester is designed,the piecewise shear deformation theroy of sandwdich vibtation energy harvester is proposed and electromechanical coupling equations are obtained using the Lagrangian equation.The proposed sandwich vibration energy harvester has lower resonant frequency and generates higher voltage output than the conventional vibration energy harvester with the same geometrical dimension.If designed for a certain resonant frequency,the proposed sandwich vibration energy harvester will be much smaller and lighter than the conventional vibration energy harvester.The influence of material properties and geometric parameters on the performance of the proposed sandwich vibration energy harvester is investigated in detail.A comparative study of different core materials for the sandwich vibration energy harvester is presented experimentally.(5)Several multi-mode sandwich piezoelectric vibration energy harvesters are designed and fabricated to validate the high design flexibility of sandwich piezoelectric vibration energy harvester.To derive the theoretical model of multi-mode sandwich piezoelectric vibration energy harvester,a conventional multi-mode vibration energy harvester is firstly designed and studied,and analytical modeling of the conventional multi-mode vibration energy harvester is proposed.Then this modeling is extended to the multi-mode sandwich vibration energy harvester.A multi-mode sandwich vibration energy harvester with two inner beams is designed,fabricated and tested.The good agreement with experimental and simulation results validates the accuracy of the theory.The parametric optimization and comparison with single-mode harvester presents that the sandwich multi-mode vibration energy harvester is more suitable to harvster energy from broadband,low-frequency and low-amplitude vibration sources.A multi-mode sandwich vibration energy harvester with three inner cantilevered beams is designed comprised of two patches of piezoelectric layer.The resonant frequencies of the energy harvester could be easily tuned to be sufficiently close and well distributed by varying the geometric parameters and the tip masses of the inner beams.This harvester further illustrates the excellent design flexibility of sandwich piezoelectric vibration energy harvester to work in various vibration environments.