Research On The Electromechanical Response Performance And Applications Of Porous Structural/viscoelastic Piezoelectric And Piezoresistive Materials

With the rapid development of intelligentialize in the industrial areas,intelligent technology currently plays an important role in the fields of aerospace,civil engineering,medicare,automotive engineering and so on.As the basis for intelligent perception and realization of mechanical system intelligence,industrial intelligentization is the extensive applications of advanced functional devices and using flexible functional materials with incentive and response functions to help or even replace human body to achieve various functions.Therefore,in automotive engineering,the automobile intelligent techniques are not depent only on the basic technology such as electrification,automation,informationization and networking,but also have huge potential demands for advanced functional materials.Although the functional materials have been developed rapidly for the past decade,how to achieve the actual demands by designing the structural performance characteristics is remaining a problem need to be solved.In order to improve and optimize the performance of the widely-used electromechanical funcational materials and to explore their potential practical applications in the field of intelligent engineering,in this dissertation,a theoretical analytical model and multiphysics finite element framework of viscoelastic multiphysical electro-mechanical coupling field is established to qualitatively and quantitatively analyse the effects of viscoelastic mechanical parameters of functional materials on their electromechanical response characteristics.The findings show that softer matrices enhance the electromechanical coupling performance because they can result in larger deformation for a given load;Additionally,the electromechanical performance of the piezoelectric funcational material is not only affected by the elastic characteristics of materials,the effects of viscous characteristics on its electromachanical conversion efficiency also cannot be ignored.And,by reasonable controlling the viscoelastic mechanical parameters of functional materials,the purpose of improving their electromechanical response performance can be achieved.Then,by taking advantages of cutting and pore structures in adjusting the mechanical behavior of functional materials,this dissertation systematically studied the electromechanical response characteristics and their applications.In this work,to take the advantages of architected cutting structure in adjusting and optimizing the mechanical properties of structural materials,the author systematically investigated how architected cut patterns affect electromechanical response performance and applications of piezoelectric materials by numerical,experimental,and analytical studies in the aspect of structure optimization,which reveals the effect of different cutting parameters on mechanical properties and electromechanical coupling properties of piezoelectric functional materials.It is found that the introduced cut patterns can achieve ideal mechanical characteristics such as high compliance(~0.12 mm/N)and stretchability,high failure strength(failure strain ~26%)and controllable Poisson's ratio(-0.56~0.38),etc.Additionally,in the dynamic loading conditions,the introduced cut patterns can efficiently reduce the structure's first order resonant frequency from 120 Hz to ~45 Hz.Therefore,the resonant frequency of PVDF piezoelectric materials can be controlled to the range of mechanical vibration frequency in daily environment,which will further enhance the electromechanical conversion output(~120%)and it can be effectively used for the recycling of low wind speed(1.8m~3.0m /s)wind energy.In addition,from the perspective of structural feature optimization,through theoretical analysis,numerical simulation calculation and experimental verification,the electromechanical response performance and applications of porous structural piezoresistive materials are systematically studied,and the mesoporous structure is designed scientifically and reasonably.In this work,the author reported a facile “casting-etching” method to fabricate an ultra-sensitive and fast response piezoresistive piezoresistive sensor using mesoporous nanocomposites,realized ultra-high pressure sensitivity(strain gauge factor,GF~306)which is 50 times higher than conventional piezoresistive carbon-nanotube composite sensor.Additionaly,the reported piezoresistive functional material sensor has fast sensing(~70 ms)ability to mechanical load in different pressure range,including water droplets(1.5 Pa~2.5 Pa),cockroach footsteps(~50 Pa),cyclic finger taping(100 Pa~500 Pa)and small weight loading(50 Pa~25 kPa).