Study On Mechanical Properties Of Straight-Arc Coupled Metamaterials With Negative Poisson’s Ratio

Honeycomb structure with negative Poisson’s ratio have auxetic characteristics,showing better mechanical properties such as scalability,energy absorption and cushioning than the traditional multi-cellular lattice structure.It is expected to be applied to solar sails in aviation,body armor and combat uniform for the defense.The microstructure design of negative Poisson’s ratio structure can effectively control and adjust its mechanical properties.At present,the microstructure design mainly focuses on the negative Poisson’s ratio mechanism of single structure,which leads to limiting the improvement on the structure mechanical properties.According to the mechanism of negative Poisson’s ratio effect combined with structural innovation,mechanical meta-structures coupled with two or more microstructural unit can be designed and constructed to obtain composite auxetic metamaterial structures with multiple mechanical advantages.This thesis introduces arc into the classical re-entrance structure to design a straight-arc coupled structure with negative Poisson’s ratio.The in-plane mechanical properties,dynamic energy absorption characteristics and deformation modes of structure are systematically investigated.In-plane elastic parameters were studied considering geometric nonlinearity based on mechanical properties analysis of unitcell.Through derivative structural design,the dynamic energy absorption characteristics and deformation mode of straight-arc coupled honeycomb structure and cylindrical structure are analyzed.The results show that the arc support in the straightarc coupled structure can enhance the energy absorption,which provides a model and theoretical basis for the better engineering application of negative Poisson’s ratio structure.The main work and research results of this thesis are as follows:(1)Energy method was used to establish a linear theoretical model of SACS,and the analytical expressions of equivalent Poisson’s ratio and equivalent elastic modulus varying with geometric parameters were obtained.The verification of the theoretical model was confirmed by numerical calculation.Based on the model,the influence of geometrical parameters(re-entrant angle θ and arc radius R)on the plane equivalent elastic parameters was studied.(2)Considering the influence of geometric nonlinearity on the negative Poisson’s ratio of the structure,a geometric nonlinearity analytical model was established based on the theory of cantilever beam with large deflection,and the nonlinear equivalent Poisson’s ratio was obtained.Compared with the linear model,the equivalent Poisson’s ratio was improved by 306.62%.The SACS model was 3D printed with Acrylonitrile Butadiene Styrene(ABS)as the base material,and the quasi-static compression experiment were carried out.The result showed that considering geometric nonlinearity the model was closer to the experimental results and can predict the actual structural deformation more accurately.(3)Based on the geometric structure of SACS,the inverse and double straight-arc coupled structures were designed as honeycomb structures.The deformation modes of the structures under different materials were obtained by numerical simulation,indicating that the supporting capacity of the arc determines the suitable substrates for honeycomb structures,and the basic material also directly affect the deformation modes.From the aspect of deformation mode,the design of the straight-arc coupled was explained,which not only uses the negative Poisson’s ratio effect of the re-entrance straight beam,but also enhances the structural stiffness with the help of the arc beam,so as to make specific energy absorption of SACS honeycomb more than twice as high as that of classical structure and curved structures.The result indicated the composite structure design of SACS honeycomb metamaterial can effectively improve the energy absorption capacity.(4)Three-dimensional cylinder structures were established by curling the series of straight-arc coupled honeycomb and the dynamic characteristics of straight-arc coupled structures were investigated.It was found that the radial thickness of SACS cylinder increases from 1 mm to 4 mm,and the specific absorption energy increases by 249%,which indicates that the increase of radial thickness can improve the stability of the cylinder.Compared with the impact of 10 m/s,the specific absorption energy of SACS at 50 m/s increases by 218%,the result showed that the straight-arc coupled structural design can play a better role in the energy absorption.