The Fabrication And Characterization Of Porous Metamaterials With Adjustable Thermal Expansion

Structural parts in the working environment of precision instruments,electronics,aerospace and other fields may need to undergo large temperature changes,which requires the material/structure to have a specific thermal expansion,and will not be affected by the external environment and produce large thermal deformation,resulting in parts and structural performance breakdown.Therefore,the material with the adjustable thermal expansion through porous metamaterial design has become a research focus in recent years.However,the problems existing in the current research are that the design and preparation of the adjustable thermal expansion porous materials and the experimental research in the temperature changing environment are still in the initial stage.In this paper,the structure of porous metamaterial with adjustable thermal deformation is systematically studied,and the combination design of ordinary engineering materials is adopted.The thermal expansion performance was studied by finite element numerical simulation and experimental characterization.The main research content is as follows.It is necessary to characterize the properties of porous metamaterial structures with adjustable thermal expansion coefficient under temperature variation.In order to measure the thermal expansion coefficient of the triangular and plane porous structures designed and prepared in this paper,a thermal expansion testing platform based on non-contact digital image correlation method was developed.Al7075,TC4,stainless steel 316 l are measured on the platform to conduct reliability calibration and testing precision measurement,proved that the set up based on the noncontact digital image correlation method of thermal expansion test platform has good precision,can for the design and preparation of double material triangle porous structure and plane porous structure of the specimen to determine the coefficient of thermal expansion.Based on the improved design of the existing triangular double-material porous structure with adjustable thermal expansion,the finite element analysis and thermal expansion test were used to verify the design.Firstly,the thermal expansion coefficient of four kinds of plastics(PP,Nylon,CPE+,PVA)with temperature change was tested by using the thermal expansion test platform.At the same time,the thermal expansion coefficient value of the corresponding brand material in the material manual is taken as the reference value.Porous structural specimens were prepared by using PVA and Nylon as two component materials through geometric size design and 3D printing.Finite element simulation and thermal expansion testing experiments were carried out.The simulation,experimental and design values were compared for error analysis.It is proved that the combination design of two engineering materials with positive thermal expansion can realize the wide range of the vertical thermal expansion coefficient from positive to negative.Because the porous structure of triangle double material with adjustable thermal expansion can only achieve the vertical adjustable thermal expansion,but in some engineering applications,the structure needs to show the isotropic coefficient of internal thermal expansion.Therefore,the adjustable thermal expansion coefficient in plane is realized by improving the design of the porous structure with adjustable thermal expansion.The plane dual-material porous structure specimens with adjustable thermal expansion were designed by using PVA and Nylon as two kinds of component materials.Then finite element simulation and thermal expansion test were carried out on the prepared structural specimens.The experimental results,the finite element simulation values and the theoretical design values are compared.The results show that the experimental values and the finite element simulation values are in good agreement with the theoretical design values.