Dynamic Response And Light Induced Deformation Of Liquid Crystal Elastomer Structures

With the continuous development of science and technology,smart soft materials become an important research interest in the field of structural design due to their unique mechanical performance.As a typical smart soft material,liquid crystal elastomer(LCE)simultaneously combines the elastic properties with anisotropic mechanical-order coupling and multi-fields sensitivity of liquid crystal.It has promising application in the fields like intelligent structural design and control,novel acousto-optical device,soft robot and so on.With the development and application of LCE device,it is more and more urgent to study the basic mechanical performance like accurate control of deformation,dynamic failure and impact dynamic response,etc.Therefore,in this dissertation,considering the mechanical-order coupling properties of LCE,the dynamic performance of LCE structures is studied,then the light induced bending and vibration of LCE structures are analyzed,and the light-electric energy harvester as well as the programmable LCE matrix are proposed.The main contents of this dissertation are as follows:1.The LCE viscoelastic foundation Timoshenko beam model and Mindlin plate model are established,and the transverse vibration performance of LCE beam and plate are studied.The influences of intrinsic parameters on the natural vibration frequency and the decrement coefficient are discussed.The effect of director rotation dissipation,rubber relaxation and viscoelastic foundation dissipation on the vibration perfomacne of LCE structures are clarified.Results show that due to the director rotation dissipation,the lower order natural frequency of LCE structure may be smaller than that of isotropic viscoelastic structure,whereas the higher order natural frequency is larger than that of isotropic viscoelastic structure.The decrement coefficient of LCE structure is always larger than that of isotropic viscoelastic structure.The increasing of foundation stiffness decreases the variation amplitude of lower order natural frequency and decrement with respect to director orientation,whilst the increasing of viscoelastic foundation dissipation changes the variation trend of lower order natural frequency with respect to director rotation time.2.The viscoelastic wave propagation in LCE Timoshenko beam is studied,and the effect of material parameters on the flexural wave and shear wave propagation characteristics is discussed.It is found that due to the director rotation dissipation,geometric dispersion is restrained with the vanishing of cut-off frequency for shear wave.The phase velocity of shear wave increases from zero to a maximum value near the cutoff frequency of isotropic viscoelastic beam,then drops sharply to a small stable value which equals to that of isotropic viscoelastic beam.The attenuation factor of shear wave increases to maximum value near the transition frequency that transits from liquid crystal to rubber plateau,then drops to a stable value which is larger than that of isotropic viscoelastic beam.3.Considering the light induced inhomegeneous strain distribution,the governing equation of motion for the LCE cantilever is derived based on the physical neutral surface,and the light driven vibration response of LCE cantilever is investigated.Moreover,by combining with the Faraday's law of electromagnetic induction,a prototype of a lightelectric energy harvester is proposed to realize the light-mechanical-electrical energy conversion.It is found that there exists critical value for the light intensity,light decay distance and light source position to trigger the periodic vibration of LCE cantilever.The ignorance of physical neutral surface deviation less estimates the critical trigger value of light decay distance and the light source positon,whereas over estimates that of light intensity.The physical neutral surface deviation is non-negligible.4.Based on the arbitrariness of the director orientation in three-dimensional coordinate,the governing equation of light induced spontaneous deformation for the simply supported LCE plate is derived.The effect of director orientation,plate geometrical size and boundary condition on the spontaneous deformation is discussed in detail.The relation between spontaneous deformation mode and the director orientation under different plate aspect ratio is established.It is found that the spontaneous deformation modes are director orientation dependent including the unimodal mode,bimodal mode and multimodal mode.Due to the boundary condition,with the decreasing of plate aspect ratio,it is easier to obtain the bimodal and multimodal mode.Based on the light induced spontaneous deformation mode of the LCE plate,the programmable LCE matrix is proposed which can be used in the field of haptic and visual display,providing new possibility for intelligent information visualization.