Structural Design And Transformation Mechanism Of 3d-printed PLA With Positive/negative Poisson Ratio

The two-dimensional lattice structure with positive/negative poisson’s ratio transition effect is called positive/negative poisson’s ratio transition structure,that is,through axial compression,the local instability in the plane of the whole structure will be caused,and then the structure from positive poisson’s ratio to negative poisson’s ratio will be generated.In this paper,we design a positive/negative poisson ratio transition structure,which can calculate and control the critical load of positive/negative poisson ratio transition by using the design of the elastic modulus and the hollow ratio of the structural material matrix.When axial compression produces deformation,each element of the two-dimensional lattice structure produces compression deformation and in-plane local instability due to mechanical coupling effect and stress concentration.The ultimate load of instability of these elements is controlled by the elastic modulus of the material matrix and the hollow rate of the element,so the critical load of positive/negative poisson’s ratio transformation of the overall structure is constantly changing.And due to the thermodynamic properties of PLA material matrix,and the two-dimensional lattice structure after the print can be compressed under different temperature conditions,thereby facilitating further adjustment base material of the mechanical parameters and then the whole structure of positive/negative poisson’s ratio change critical load,including the overall structural plane bending,structural failure warning limit load.In addition,the axial compression process of these two-dimensional lattice structures is analyzed by Abaqus numerical simulation.Finally,based on the model of electrostatic field and gravitational field,an idealized mathematical model of the whole structure is established and the plane stress state of the whole structure is derived,and the calculation method of the plane stress of the whole structure before and after the positive/negative poisson ratio transition effect is analyzed by using the theory of elasticity and the theory of material mechanics.In the third chapter,the geometric model design and method of two-dimensional lattice structure are mainly introduced.The axial compression deformation of the whole structure and the element is verified by Abaqus software simulation.We design a two-dimensional lattice structure which is induced by axial compression to produce positive/negative poisson’s ratio transition.Viscoelastic model is adopted to simulate the thermal mechanical behavior of PLA,through the thermal-mechanical properties testing results confirmed that the thermodynamic properties of poly(lactic acid)(PLA),and adopted in the Abaqus simulation with experimental environment and load boundary conditions,the same temperature and gradient modulus gradient hollow ratio and the modulus of elasticity material matrix and positive/negative poisson’s ratio change critical load and the relationship between them.The Abaqus numericalsimulation results reveal the deformation characteristics of this two-dimensional lattice structure under axial compression,and prove that it has the characteristics of positive/negative poisson ratio transformation.In this paper,the fourth chapter,mainly through the axial compression experiment and numerical simulation of Abaqus simulation calculation is studied under different temperature conditions and different hollow ratio of axial compression deformation of two-dimensional lattice structure,from two aspects of the experiment and simulation confirm the 3 d printing polylactic acid positive/negative poisson’s ratio change of the structure of the transformation mechanism,the effect of positive/negative poisson’s ratio changes of two necessary conditions.Based on the experimental data and the simulation results,a method for measuring the critical load of positive/negative poisson ratio transition is obtained.Based on the above results,the positive/negative poisson ratio transition structure of the matrix of the anisotropic material was designed.The simulation results show that the positive/negative poisson ratio transition structure of the matrix of the anisotropic material can get rid of one of the necessary conditions and carry out structural design under the condition of unrestricted thickness.In the fifth chapter,we use the axial compression simulation and experimental data of the two-dimensional lattice structure,based on the theory of mechanics of materials and elasticity,and further establish the mathematical model of the plane stress state of the whole structure.The influences of the elastic modulus of the matrix and the hollow ratio on the transition critical load are compared,and it is proved that the ideal formula can be used to solve the transition critical load of the transition structure with a given positive/negative poisson’s ratio of the matrix and structure size.The results provide an effective way for the design of similar structures,prediction of mechanical behavior,strength checking and damage warning.