Study On The Static And Dynamic Mechanical Properties Of 3D Re-entrant Honeycomb Polyamide Structure

Auxetic materials and structures have excellent mechanical properties and great potential application value due to their negative Poisson’s ratio characteristics.The Made in China 2025 Initiative explicitly calls for greater innovation in new materials such as metamaterials and additive manufacturing.The research of auxetic materials and structures in mechanical metamaterials is in full swing,however,there is still a long way to go.The main reason is that the fundamental properties of materials and structures with negative Poisson’s ratio have not been studied well yet.As a classic auxetic structure,the study on static and dynamic properties of re-entrant honeycomb structure will be helpful to further understand the properties of other auxetic materials.The three-dimensional re-entrant honeycomb structure is more complex than the two-dimensional structure.Although a lot of related researches have been carried out,they are mainly based on the two-dimensional structure,and there are few researches on the threedimensional structure,especially on the dynamic performance.Therefore,it is necessary to study the static and dynamic mechanical properties of 3D re-entrant honeycomb structure.With the spring breeze of additive manufacturing,it is possible to manufacture 3d complex structures.In this paper,different geometric re-entrant honeycomb specimens made of polyamide were fabricated by using additive manufacturing technology.Uniaxial quasi-static compressive tests were conducted on the specimens,3D finite element(FE)simulations were carried out by using a commercial finite element software(ANSYS)and an analytical model of 3D re-entrant honeycomb unit cell under uniaxial compression was proposed.In addition,in view of the lack of dynamic performance research,this paper focuses on the research of SHPB experimental test technology for the polyamide re-entrant honeycomb structure,and then studies the dynamic mechanical properties and impact energy absorption.The main achievements are as follows:1.Uniaxial quasi-static compression test was conducted on the three-dimensional reentrant honeycomb specimens,and the deformation morphology,stress-strain curves and Poisson’s ratios were analyzed and compared.The results show that 3D re-entrant honeycomb unit experienced the deformation modes such as compression and bending deformation of the vertical struts,bending and shearing deformation of the oblique struts.After comparing the specimens with different geometric parameters,it was found the smaller re-entrant angle led to higher Young’s modulus and the structure was more likely to experience global instability failure,and Young’s modulus increased with the rising horizontal length of vertical strut.In addition,the specimens exhibited negative Poisson’s ratios between-0.105 and-0.193.2.The finite element models were established by using ANSYS software and calibrated with the experimental results by comparing the stress-strain curves and deformation patterns.The stress distributions were extracted to reveal the mechanical behavior and the calibrated numerical models can be used to conduct parametric study.In addition,a new analytical model of 3D RH unit cell based on Timoshenko beam theory and large deflection beam theory was proposed to investigate the deformation mechanism of the unit cell with different geometric parameters under uniaxial compression,and the analytical model can be used to qualitatively predict and assist in structural design.3.PMMA bars with matched wave impedance with the test specimen were chosen to do SHPB experiments.Due to the wave attenuation caused by PMMA material,the waveform at the interface positions of PMMA bar cannot be directly replaced by the waveform at the strain gauge positions,so it is necessary to conduct SHPB dynamic test on the PMMA bar.An improved Lagrangian method was used to process the strain time-history data collected from SHPB test of PMMA bar to obtain the stress time-history and velocity time-history data.Meanwhile,ZWT viscoelastic constitutive model is used to calibrate constitutive parameters of PMMA bar material,and the constitutive equation of PMMA bar material is obtained.Then the stress,strain and particle velocity data at each position on the PMMA bar are calculated by using the characteristic line method,which is compared with the data obtained by Lagrange method to realize the closed-loop test.4.An improved generalized Lagrangian method achieved mutual derivation among stress,strain,and particle velocity.Aiming at how to control the numerical errors,five types of numerical error that appeared in the numerical calculation were analyzed,and feasible solutions were proposed to control them,including optimized construction and multi-step iterative calculation.A case study of concrete material under impact loading was performed,and a onedimensional linear elastic bar model and a nonlinear viscoelastic bar model were established,which verified the validity of the improved Lagrangian method.5.The SHPB impact tests were carried out on the three-dimensional re-entrant honeycomb specimens made of polyamide.The improved Lagrangian method was used for data processing,and the incident strain wave and transmitted strain wave at the interface between the bar and the specimen were calculated.Then the dynamic stress-strain curve of the tested specimens can be obtained through the traditional SHPB theory.According to the waveform curves,the dynamic characteristics of the specimens were analyzed,and the stress-strain curves and the energy absorption capacity of the specimens with different impact velocities and different geometric parameters was analyzed.Through the analysis of the incident,reflection and transmission waveform,the propagation characteristics of the wave in the PMMA bars and the energy absorption characteristics of the specimens are reflected.And the impact loading process can also be clearly understood and analyzed.