Multifunctional And Smart Design Of Composite Materials With Adjustable Coefficient Of Thermal Expansion

Most natural materials satisfy the basic physical properties of thermal expansion and cold contraction.However,in the service process of high-end equipment such as satellites,hypersonic aircrafts and precision instruments,the structure is subject to the environmental temperature change and the demand of high precision,so the thermal deformation needs to be controlled in real time and accurately.Therefore,the development of composite materials with minimal thermal expansion(or even zero thermal expansion)and negative thermal expansion,as well as the development of multifunctional and intelligent composite materials with arbitrary adjustable expansion coefficient have become the research hotspot in the field of scientific research.Advanced manufacturing technologies(such as 3D/4D printing and micro-nano manufacturing)make it possible to prepare the advanced composite materials(also known as metamaterials and superstructures)with extraordinary properties designed by human beings.In order to improve the allowable temperature range of materials,a multifunctional design method of high allowable temperature range of the zero expansion composite material considering the stiffness characteristics is proposed.The nonlinear dynamic jump characteristic of the double-layer shallow shell structure under the condition of environmental temperature change is studied,the design of a smart honeycomb sandwich structure with adjustable between positive and negative thermal expansion is proposed.The specific contents and conclusions are as follows:(1)Design of higher allowable temperature range for zero thermal expansion composites considering stiffness characteristic.The macroscopic zero thermal expansion of material could be obtained through combining two kinds of materials with different positive thermal expansion coefficients within a unit cell.These composites usually possess higher thermally geometric stability in the large temperature fluctuation.However,it readily produces excessive thermal stress on the interface between the two constituent materials and therefore limits the allowable temperature range of the material.A new evaluation index of the maximum thermal stress of unit temperature rise was resorted to perform allowable temperature and stiffness analyses for the three types of typical bending-dominated zero expansion materials.Both the analytic and numerical simulation methods were adopted and the influences of cell design parameters on these aspects are also discussed.The results show that when the designed zero expansion attribute is achieved,the high stiffness and high allowable temperature range can be obtained at the same time if the reasonable constituent materials and structural parameters are selected.(2)Research on nonlinear dynamic jump characteristics of the double-layer shallow shell structure driven by environment temperature.Changing the microstructure of composite materials is an effective way to realize the variable macroscopic equivalent performance and an important way to realize the intellectualization of composite materials.The key problem is to find the structural form with structural variable characteristics under external excitation and to establish the corresponding performance characterization method.In this paper,the double-layer shallow shell structure with bistable characteristics driven by environmental temperature is proposed,and the influence of designable parameters(material parameters,geometric parameters,etc.)on nonlinear dynamic jump characteristics is discussed by developing numerical methods.With the controllable low jump temperature as the design goal,the shape of the double-layer shallow shell is optimized.The dynamic jump characteristics of quadrilateral and hexagon double-layer shallow shells which are easy to be spliced are analyzed,which provides a basis for further smart composite material design.(3)Design of smart honeycomb sandwich panel with adjustable in-plane coefficient of thermal expansion between positive and negative.Based on the dynamic jumping characteristic of the proposed double-layer shallow shell structure,an innovative design scheme of smart honeycomb sandwich panel was proposed.The design scheme not only has the high carrying capacity of sandwich honeycomb panel,but also has the smart characteristic of adjustable thermal expansion coefficient.The rule of the equivalent coefficient of in-plane thermal expansion driven by environmental temperature is studied by numerical methods.The results show that the newly proposed smart honeycomb sandwich panel can not only realize the adjustment of the equivalent coefficient of in-plane thermal expansion between positive and negative,but also realize the conversion between positive and zero,positive and zero.This research provides a basis for further realization of precise and intelligent control of smart honeycomb sandwich panel.