Negative Poisson's Ratio in Modern Functional Materials

Materials with negative Poisson's ratio attract considerable attention due to their underlying intriguing physical properties and numerous promising applications, particularly in stringent environments such as aerospace and defense areas, because of their unconventional mechanical enhancements. Recent progress in materials with a negative Poisson's ratio are reviewed here, with the current state of research regarding both theory and experiment. The inter‐relationship between the underlying structure and a negative Poisson's ratio is discussed in functional materials, including macroscopic bulk, low‐dimensional nanoscale particles, films, sheets, or tubes. The coexistence and correlations with other negative indexes (such as negative compressibility and negative thermal expansion) are also addressed. Finally, open questions and future research opportunities are proposed for functional materials with negative Poisson's ratios.     

Perforated Sheets Exhibiting Negative Poisson's Ratios

Sheets made from readily available conventional materials containing diamond or star shaped perforations are shown to exhibit various Poisson's ratio values which could also be negative (auxetic). This behavior may be exhibited in both tension and compression and can be explained through models based on “rotating rigid units.” This provides an easy manner for the manufacture of auxetic or conventional systems at any scale which can be tailor made to exhibit particular values of the Poisson's ratio.     

TC4负泊松比复合结构的人工骨力学性能调控研究

目的 基于不同变形机制的负泊松比结构优化设计新型复合多孔结构样件,增加力学性能的调控维度,以满足人体骨低弹性模量的匹配要求。方法 用内凹多边形替代手性结构的圆环,以获得新型的复合胞元结构。利用选区激光熔化成形技术制备负泊松比多孔人工骨样件,通过压缩实验揭示胞元结构类型、结构参数、孔隙率对屈服强度、弹性模量的影响规律,评测不同结构样件与人体骨间的力学性能匹配程度。结果 当孔隙率为65%～85%时,复合结构样件的成形质量、力学性能基本介于手性结构的和内凹结构的之间,且与孔隙率密切相关。手性结构、内凹结构和复合结构的弹性模量分别为2.39～4.64、1.12～3.77、1.01～3.47 GPa,屈服强度分别为65.19～223.06、45.25～195.81、26.54～143.58MPa。复合结构的弹性模量随环径和内凹角度的增大而减小。当孔隙率为75%时,环径由2.4 mm变至2.0 mm,弹性模量由2.651 GPa降低至2.082 GPa。当内凹角度由85°变至65°时,弹性模量则由3.566GPa降低至1.982GPa。结论 复合胞元结构可以融合材料特性,增加调控维度,进而匹配人工...     

Mechanical Properties of a Novel Zero Poisson's Ratio Honeycomb

In this paper, a novel honeycomb is proposed by embedding a rib into every cell of the existing zero Poisson's ratio (ZPR) configuration, semi re‐entrant honeycomb (SRH). Analytical model is developed to investigate the in‐plane mechanical properties of the new honeycomb, and the resulting theoretical expressions are compared with the experimental tests and numerical results obtained from two different finite element (FE) models (3D beam model and 3D solid model), leading to a good correlation. FE analysis, analytical modeling, and experimental tests of the new honeycomb show that it can achieve ZPR effect in two principal directions. For further studies, parameters analyses are carried out to explore the dependence of the in‐plane mechanical properties versus the geometric parameters. The results show that bending is the dominated deformation model when the new honeycomb is compressed along the x‐ direction, while stretch controlled in the y‐ directional compression. It is remarkable that the new proposed honeycomb features superior specific stiffness and more flexible in mechanical properties tailoring compared to the other ZPR honeycombs in the literature. Given these benefits, the new honeycomb may be promising in some practical applications.

     

A Decomposition Method for the Analysis of Viscoelastic Structural Dynamics with Time‐Dependent Poisson's Ratio

Abstract: This paper presents a decomposition method for the dynamic analysis of elastic–viscoelastic composite (EVC) structures with time‐dependent Poisson's ratio. The analysis splits the viscoelasticity matrix with time‐dependent Poisson's ratio into two matrices in a simple form in which the time‐dependent Poisson's ratio does not appear. The decomposition simplifies the process of dynamical analysis for EVC structures with time‐dependent Poisson's ratio. The approach also makes it possible to apply existing analysis methods for constant Poisson's ratio structures directly to structures with time‐dependent Poisson's ratio. Based on the numerical results of three case studies, it is found that the time‐dependent Poisson's ratio has little influence on the structure's natural frequencies and damping properties. Therefore, it could be concluded that the effect of time‐dependency in Poisson's ratio may be ignored in the EVC structural dynamic analysis without introducing notable errors.