| As a new kind of mechanical metamaterial,negative compressibility material has a very broad application prospect in aerospace,deep-sea exploration,highly sensitive sensors,intelligent materials and biomedicine due to its abnormal mechanical response characteristics.The so-called negative compressibility means that when materials or structures are subjected to hydrostatic pressure,they will have reverse expansion in one or more directions in the direction of force.At present,the relevant research in the field of negative compressibility materials at home and abroad is still at the initial stage.It has been found that the types and quantities of materials or structures with negative compressibility are relatively limited,and the research content mainly focuses on the design of negative compressible materials and two-dimensional negative compressible structures.The relevant research on 3D negative compressible structures is not sufficient at present.Although the increase of dimensions will lead to a significant increase in analysis complexity,relevant research has shown that 3D structures can produce greater negative compressibility and have more abundant multiple negative characteristics.Therefore,it is of great scientific significance to carry out innovative design and research on negative compression characteristics of three-dimensional negative compression structures for enriching the configuration performance of three-dimensional negative compression structures,improving the negative compression of structures,and further promoting the rapid development of negative compression design theory.In view of the problems existing in the research of the above three-dimensional negative compressibility structure,this paper proposes a way to simulate the natural crystal structure to construct a three-dimensional structure with negative compressibility characteristics,and obtains the corresponding hinge type crystal like structure by setting flexible hinges at both ends of the rod,so that it can meet the setting of the ideal hinge model and achieve the goal of complete crystal like design.The main research contents include:(1)Taking the typical two-dimensional wine-rack structure as the research object,two kinds of hinging wine-rack crystal-mimic structures were constructed by adding straight beam type and straight circle type flexible hinges at both ends of the rod.First,the expressions of the mechanical characteristics of the two hinging structures are derived,and then they are verified by finite element simulation and uniaxial compression experiments.Finally,the hinging wine-rack structure with straight beam type flexible hinges is selected as the basis of the follow-up crystal-mimic design,and its parametric discussion is carried out,and the effects of various geometric parameters of the model on its mechanical characteristics are obtained.The results show that the deformation mechanism of the two-dimensional hinging wine-rack structure conforms to the setting of the idealzed hinging model and has greater negative linear compression characteristics.At the same time,the thickness of hinge is the most sensitive parameter in hinge design,and the angle parameter is the most important parameter affecting the negative compressibility of structure.(2)Taking the three-dimensional tetragonal octahedral structure as the research object,the hinging crystal-mimic structure is extended to the three-dimensional negative compressibility structure field,and the hinging crystal-mimic tetragonal octahedral structure is constructed by adding flexible hinges at both ends of the rod.First,the expressions of the mechanical characteristics of the three-dimensional structure under the idealzed hinging model and the flexible hinge form are derived,and then verified by finite element simulation and uniaxial compression experiments.Finally,the mechanical characteristics and negative compressibility characteristics of the three-dimensional hinging structure are also discussed parametrically.The results show that the three-dimensional hinging tetragonal octahedral structure also conforms to the setting of the idealzed hinging model,and has many mechanical properties such as negative linear compressibility,negative area compressibility and negative Poisson’s ratio.(3)Based on the hinging tetragonal octahedral structure,four new three-dimensional crystal-mimic models with negative compressibility characteristics are constructed by adding rods in the horizontal and vertical directions.Taking the same analysis process as that of tetragonal octahedral structure,the mechanical property expressions of these four crystal-mimic structures are given and verified by finite element simulation and uniaxial compression experiment.Then,the influence of geometric parameters on the mechanical properties of each model is analyzed by using theory model and finite element model.Finally,the influence of rod changes on the negative compressibility characteristics of the model is discussed in combination with tetragonal octahedral structure.The results show that these four models also have negative linear compressibility,negative area compressibility and negative Poisson’s ratio.And increasing the rod in any direction will increase the anisotropy in this direction,thus increasing the negative compressibility characteristics in this direction and weakening the negative compression characteristics in other directions.(4)Based on the hinging tetragonal octahedral structure,three new three-dimensional crystal-mimic models with negative compressibility are constructed by changing the type of crystal system.The same analysis process as that of tetragonal octahedral structure is adopted.First,the mechanical characteristic expressions of these three structures are given and verified by finite element simulation and uniaxial compression experiment.Then,the theoretical model and finite element model are used to analyze the influence of geometric parameters on the mechanical characteristics of each model.Finally,the influence of crystal system changes on the negative compressibility characteristics of the models is discussed in combination with the tetragonal octahedral structure.The results show that these three models also have negative linear compressibility,negative area compressibility and negative Poisson’s ratio,and adopting a weaker symmetry crystal system and a looser arrangement can increase the negative compressibility characteristics of the model.(5)Based on the existing rutile crystal and Kelvin lattice,three-dimensional crystal-mimic models corresponding to the two crystal structures can be constructed by adding flexible hinges.Taking the same analysis process as that of tetragonal octahedral structure,the mechanical characteristics expressions of these two crystal-mimic structures are given and verified by finite element simulation and uniaxial compression experiments.Then,theoretical model and finite element models are used to analyze the influence of geometric parameters on the mechanical characteristics of these two model.Finally,the influence of geometric parameters on the negative compression characteristics of these two model are analyzed by theoretical model.The results show that both of the two crystal-mimic models have negative linear compressibility and negative area compressibility.In addition,the rutile crystal-mimic model has negative Poisson’s ratio,and the Kelvin crystal-mimic model has the largest negative linear compressibility characteristics.In the crystal-mimic design of existing crystal structure,both parameter generalization and modification design can greatly enrich the configuration performance of the model,increase the number of negative compressibility structures and improve the negative compressibility of the structure. |
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