Research On The Structural Design And Application Of Mechanical Metamaterials

With its rapid development in the electromagnetic field,metamaterial is not only a type of devices,it has become a concept of design.By carefully designing the microstructure of the element,researchers could control the overall performance of artificial structural materials.Moreover,its application is not only limited in the controlling of the transmission of electromagnetic wave,it has propagated into every field of physics.Based on the basic design concept of metamaterial,this paper studies its great potential applications in the mechanical engineering field.First,the thesis has proposed a negative thermal expansion mechanical metamaterial by combining the anti-chiral structure with a bi-material ligament.By adjusting the node radius,the difference between the thermal expansion coefficient of the component materials,the thickness and the length of ligaments,tunable effective linear thermal expansion of the metamaterial could be achieved.Its thermal property has been proved by both simulation and experiment,which demonstrate that the artificial structure presents an isotropic negative thermal expansion property,and the thermal shrinkage performance can be controlled by changing the designing parameters of the structure.This is the first three-dimensional isotropic artificial negative thermal expansion metamaterial that has been demonstrated by experiment at home and abroad.It lays the foundation for accurately controlling the thermal expansion of materials and ultimately achieving zero expansion of devices in industry.Second,a metamaterial that can magnify the thermal expansion of materials was realized by adopting the principle of differential lever.The thermal expansion coefficient of the conventional materials could be enlarged by controlling the geometric dimensions of the differential lever units and the design parameters of the flexural hinge.The magnification is determined by the size parameters of the element structure.Combined with the design of negative thermal expansion metamaterial,a full range of control of the thermal expansion could be achieved.In this way,researchers can design structural materials according to their specific application in industry.Third,a multi-stable structure has been designed by introducing the metamaterial concept into the design of “phase transition” materials.By combining a snap-fit structure with oblique beam unit,a structure with two stable configurations has been constructed.Through simulation,the thesis studied the relationship between the mechanical energy trapped by the element structure and the parameters of the snap-fit.On this basis,an array structure was fabricated,which was constructed with gradient parameters.Experimental results demonstrate the multi-stable performance of the array sample.More importantly,the multi-stability performance of the structure can be adjusted not only by changing the size parameters of the unit structure,but also by changing the friction coefficient between the plug and the groove by surface lubrication treatment.The proposed model has broad application prospects in industry such as the protection of people or precision instrument in engineering accidents.It has the advantages of low cost,simple manufacturing process,convenient manipulation and reusability.Finally,this thesis introduces thermal expansion materials into dielectric electromagnetic metamaterial.The thermal effect of the interlayer could compensate the effect of temperature on the shifting of resonant frequency of the dielectric meta-atom.Therefore,a precise control of the coefficient of frequency temperature of electromagnetic metamaterials could be achieved.In addition,by using the dielectric electromagnetic metamaterials,small stress and strain inside soft materials could be measured,solving the problem of wireless strain detection in mechanical field.Since all of the materials we used in the design of the meta-atom are biocompatible,this structure can be used to measure small stress and strain inside the biological tissues.