Structural Design Of Deformable Negative Poisson’s Ratio Based On 4D Printing

Negative Poisson’s ratio structure is an anomalous mechanical structure.This type of structure not only has anomalous negative Poisson’s ratio property,but when it is longitudinally stretched(compressed)by the outside world,it will produce lateral expansion(shrinkage).It also absorbs energy,It has excellent mechanical properties in terms of indentation resistance,elastic modulus and shear modulus.Shape memory polymer is an intelligent composite material that can respond to external stimuli.The material not only has deformable properties but also has good biocompatibility.It is used in biomedicine,flexible electronic components,aerospace,Optical components and other fields have broad application prospects.In this paper,the research on negative Poisson’s ratio structure is based on the existing negative Poisson’s ratio chiral structure.By changing the geometric structure of the beam in the hand-shaped negative Poisson’s ratio grid structure,the fractal geometry principle is introduced into the design of the structure.The chiral negative Poisson’s ratio structure of the graded structure and shape memory polymer are used to make the structural model with deformability,in order to improve the tensile expansion performance and large deformation ability of the negative Poisson’s ratio structure.First,the relevant parameters of the materials used are obtained through experimental means,and then the finite element analysis is used to simulate the shape memory process of the materials using the viscoelastic model.The theoretical calculation model of the equivalent modulus of the negative Poisson’s ratio structure is deduced.Finally,the negative Poisson’s ratio properties of the structure are verified through experiments and finite element methods.The contents of this paper are as follows:(1)First,the glass transition temperature of SMP is tested.The test is carried out using dynamic mechanical analysis(DMA)experiments.The results obtained show that the glass transition temperature of the materials used in the experiment is 70℃.In addition,uniaxial tensile experiments and stress relaxation experiments at different temperatures were performed on the materials to characterize the thermodynamic properties of shape memory polymers.A cyclic loading-unloading experiment was conducted on the experimental material,and the stability of the material after undergoing cyclic mechanical load was tested by this experiment.Finally,a shape memory cycle experiment was carried out on the shape memory polymer.The main purpose of the experiment was to characterize the shape memory cycle process of the material.The experiment confirmed that the stress of thematerial was basically stable after 40 cycles.(2)The equivalent flexibility matrix and the Poisson’s ratio calculation formula of the negative Poisson’s ratio structure with fractal structure involved in this paper are derived.First,the first-order microwire model without fractal geometry is derived using Castigliano’s theorem Formula of flexibility matrix,and the recursion matrix is ??summarized through the geometric relationship of the structure,and then the flexibility matrix containing n-level fractal structure microwires is derived,and finally the Poisson’s ratio of the whole structure is obtained by the method of static balance analysis Since the square mesh structure has anisotropy,two typical directions were selected at a time,that is,when the axial tension is applied in the 0° direction and the 45° direction,the object is deduced,and the structure in these two directions is obtained.The equivalent Poisson’s ratio calculation formula.(3)The viscoelastic behavior of the shape memory polymer is described,and the shape memory and shape memory processes of the polymer are simulated using ABAQUS software.The finite element simulation results are in good agreement with the experimental results.In addition,the ABAQUS software was used to perform the tensile simulation of the soft network negative Poisson’s ratio structure,and the results were compared with the tensile experiment results.The results of the comparison showed that it was compared with the negative Poisson’s ratio structure without secondary structure.,The secondary structure of negative Poisson’s ratio structure enhances the negative Poisson’s ratio effect of the whole structure,where the maximum value of the absolute value of the negative Poisson’s ratio of the structure is the largest when m=8,indicating that the number of two-dimensional structures is negative to the structure.The enhancement effect of the Songbi effect is the strongest.In addition,as the number of two-dimensional structures of the structure increases,the ultimate deformation of the whole structure gradually increases,which means that the increase of the number of two-dimensional structures enhances the ability of negative Poisson’s ratio large deformation.