Composite Lattice Materials And Structure With High Stiffness And Specific Thermal Expansion

Thermal expansion coefficient(CTE)is the key physical parameter to quantify thethermal behavior of materials.It characterizes the change of material / structure volume due to the changes of the environment temperature.Zero/low expansion materials are urgently needed to avoid the loss of original design accuracy in high-precision structures serving under intense temperature changes.In order to avoid the failure of incompatible thermal expansion of multi-material components to destroy the integrity of structures and cause functional failure,it is necessary to develop materials with specific coefficient of expansion.In order to achieve greater driving force when actuators and other structures are changing in temperature,materials with large expansion coefficient need to be developed.Therefore,materials or structures are required to have a specific CTE,meanwhile as structural members,good mechanical properties are necessary.By adjusting the constituents/distribution and microstructure of the material,the structure can meet the specific performance.Advanced manufacturing process,especially the development of additive manufacturing technology,this technology provides a powerful support for precision manufacturing of structures.How to design the microstructural to make metamaterials have high stiffness and specific thermal expansion become a very hot issue in recent years.Based on these demands,two kinds of composite materials with unbounded thermal expansion coefficient and a sandwich plane structure with zero expansion inside the surface are presented in this paper.The specific contents and conclusions are as follows:(1)Design of composite material with unbounded thermal expansion coefficient.Triangular cell lattice metamaterials composed of bi-layer curved rib elements(called the Lehman-Lakes lattice)possess unbounded thermal expansion,high stiffness.However,the requirement of such lattice metamaterial must be pin-connected joints.The fabrication complexity makes them less than ideal for consideration especially on microstructural scales.In this study,the joint-bonded triangular cell lattice metamaterial(JTCLM)is presented,the thermomechanical properties of JTCLM are given by the closed-form analytical solution.The validity of the analytical models is illustrated and proved by the numerical simulations.Compared with the Lehman-Lakes lattice,the JTCLM with zero CTE has about 34.2%improvement in stiffness and simultaneously have 17% reduction in weight.The stiffness ofthe JTCLM has a moderate reduction when achieving the same large positive or negative CTE.(2)Stiffness enhancement design of dual-constituent triangular composite lattice with unbounded thermal expansion via chiral.In order to improve the stiffness properties of JTCLM,a new design of triangular chiral lattice structure based on antisymmetric deformation of ribs is presented in this paper.Compared with the Lehman-Lakes lattice,the new proposed lattice with zero CTE has about 2.9 times improvement in stiffness,when achieving the same large positive or negative CTE the whole stiffness has 1.2 times improvement.Compared with the JTCLM lattice,the new lattice with zero CTE has about 2.2times improvement in stiffness.Besides,the thermomechanical coupled model of new proposed lattice metamaterials are given by the closed-form analytical solution.The validity of the analytical models is illustrated and proved by the numerical simulations.The new proposed lattice have good manufacturability and multifunctional properties.(3)New design of bi-material non-porous plate with ultralow in-plane thermal expansion.In this paper,a sandwich plate structure design for zero expansion is presented.Composition of materials with different CTE,the ultralow in-plane unidirectional and bidirectional zero expansion is realized by the bending mechanism of the bi-material ribs.In this paper,a theoretical formula for the unidirectional zero expansion of bi-material plates is given,then make a verification analysis.On the premise of selecting structural materials,the influence of structural dimension parameters on thermal expansion coefficient is given.Extended the realization mechanism of unidirectional zero expansion structure to bidirectional zero expansion structure,and the parametric influence diagram of bidirectional zero expansion is provided.This structure can achieve zero expansion in the surface and easy to manufacture,keep the temperature inside the structure act as a seal in thermal protection system.