The Design And Characterization Of Zero/Negative Thermal Expansion Cellular Structures

In some high temperature, low temperature and fast-changing temperature situation, the influence of the thermal deformation on the stability of engineering structure and the precision of precision detection equipment is very serious. This paper has carried on the detailed research on the zero/negative thermal expansion cellular structure. The purpose of this paper is using common materials to design a zero/negative thermal expansion structure which is not only having good bearing performance but also having zero thermal expansion in some directions.This paper divide the zero/negative thermal expansion structure into three categories, including the bi-material beam zero/negative thermal expansion structure, the triangular unit zero/negative thermal expansion structure and the bi-material curved plate zero/negative thermal expansion cellular structure.For the bi-material beam zero/negative thermal expansion structure, this paper designs a kind of "I" bi-material beam. Compared with the bi-material beam in the literature, the "I" bi-material beam can solve the stress concentration problem in the two materials contact place, and the "I" bi-material beam is easy to be prepare.In view of the triangular element zero/negative thermal expansion structure, this paper analyzes the influence of the hinge and solid joint on the triangle unit thermal expansion coefficient. Study found that when the ratio of length and thickness is under 1/10, the thermal expansion coefficient of hinged triangle unit and fixed triangle unit is very close, which we can use the expression of hinged triangle unit to solve the thermal coefficient of the fixed triangle unit; And if the triangle unit was more "flat", the phenomenon of the negative thermal expansion will be more obvious on the vertical direction.For the bi-material curved plate zero/negative thermal expansion cellular structure, this paper analyzes the characteristics in thermal deformation. Then, using the energy method deduce the theory solution of the thermal expansion coefficient.In view of the three kinds of structure, this paper has carried on the detailed theoretical derivation, and studied the influence of the geometric parameters and the material parameters to the thermal expansion coefficient. Based on the above analysis, this paper design a lattice structure model which is easy to be implement, and can realize zero thermal expansion characteristic in some directions or isotropic zero thermal expansion. For the application of this design in engineering, this paper provides a theoretical basis for the design of zero/negative thermal expansion structure and provides a systematic ideas for design zero/negative thermal expansion cellular structure.