| Any material with resistivity up to 10 MΩ?m is referred to as dielectric in general.The dielectric materials play important roles in electrical,electronic and artificial intelligent techniques,which are often used as an important part of capacitors or sensors.However,in practical applications,some typical natures of a material are polarization,energy loss and breakdown in an electric field,which seriously reduces the service life of dielectric materials.To study the mechanical behaviors of dielectrics under electric field is conducive to prolong service life and optimize design of dielectrics.This thesis studied the bending deformation behaviors of bone,a biological dielectric material,polymethyl methacrylate and polyethylene under an alternative electric field.At first,time responses of bending deflections and surface temperature rise of bone in an alternating electric field have been measured,and its mechanism were explained.The experimental results shown that with the continuous loading time,the free end deflection of the bone cantilever beam increases slowly and finally tends to be stable.The bending deformation of bone was accompanied by obvious temperature rise.The temperature rise is due to the obvious dielectric loss of collagen fiber,an organic component in bone,under the action of alternating electric field.The reason for the bending deformation is that the collagen and hydroxyapatite in bone are distributed asymmetrically along the thickness direction.It means hydroxyapatite retains most of the polarization charge and the same charge repels each other.Collagen fibers generate a lot of heat,and the thermal expansion coefficients of the two components are different.Therefore,an alternating electric field results in the bending deformation of bone.Then,we studied the bending deformation of classic dielectric materials polymethyl methacrylate and polyethylene under an alternating electric field,and its mechanism were explained.The experimental results shown that time responses of bending deflections of them were similar to bone,but there was no obvious temperature rise on the surface of the specimen.Different surface treatments of the same material shown different deformation characteristics,and the deflection of the free end of the sample changes abruptly at the moment of loading and unloading.Due to different charge injection velocities and uneven charge distribution along the thickness direction,the sample will be deformed,but the deflection mutation cannot be explained.This thesis proposed a force galvanic model,thus the bending deformation of classical dielectric materials is due to the interaction of charge rejection theory and force-electric couple model.The series experiments results reveal the deformation mechanisms of dielectric materials in various aspects.It is helpful to understand dielectric electrical properties in the research of reducing energy loss and prolonging service life. |
