Metamaterials have been receiving an increasing amount of interest in recent years. As a type of metamaterial, pentamode materials (PMs) approximate the elastic properties of liquids. In this study, a finite-element a...Metamaterials have been receiving an increasing amount of interest in recent years. As a type of metamaterial, pentamode materials (PMs) approximate the elastic properties of liquids. In this study, a finite-element analysis was conducted to predict the mechanical properties of PM structures by altering the thin wall thicknesses and layer numbers to obtain an outstanding load-bearing capacity. It was found that as the thin wall thickness increased from 0.15 to 0.45 mm, the compressive modulus of the PM structures increased and the Poisson’s ratio decreased. As the layer number increased, the Poisson’s ratio of the PM structures increased rapidly and reaches a stable value ranging from 0.50 to 0.55. Simulation results of the stress distribution in the PM structures confirmed that stress concentrations exist at the junctions of the thin walls and weights. For validation, Ti–6Al–4V specimens were fabricated by selective laser melting (SLM), and the mechanical properties of these specimens (i.e., Poisson’s ratio and elastic modulus) were experimentally studied. Good consistency was achieved between the numerical and experimental results. This work is beneficial for the design and development of PM structures with simultaneous load-bearing capacity and pentamodal properties.展开更多
<div style="text-align:justify;"> Coding metasurface draws amounts of research interests due to its potential for achieving sophisticated functions in wave manipulation by using simple logical unit cel...<div style="text-align:justify;"> Coding metasurface draws amounts of research interests due to its potential for achieving sophisticated functions in wave manipulation by using simple logical unit cells with out-of-phase responses. In this paper, we present a novel acoustic coding metasurface structure for underwater sound scattering reduction based on pentamode metamaterials. The metasurface is composed of two types of hexagonal pentamode unit cells with phase responses of 0 and π respectively. The units are arranged in random 1-bit coding sequence to achieve low-scattering underwater acoustic stealth effect. Full-wave simulation results are in good accordance with the theoretical expectation. The optimized arrangement resulted in the distribution of scattered underwater acoustic waves and suppression of the far field scattering coefficient over a wide range of incident angles. We show that pentamode-based coding metasurface provides an efficient scheme to achieve underwater acoustic stealth by ultrathin structures. </div>展开更多
Biomimetic metallic biomaterials prepared for bone scaffolds have drawn more and more attention in recent years.However,the topological design of scaffolds is critical to cater to multi-physical requirements for effic...Biomimetic metallic biomaterials prepared for bone scaffolds have drawn more and more attention in recent years.However,the topological design of scaffolds is critical to cater to multi-physical requirements for efficient cell seeding and bone regeneration,yet remains a big scientific challenge owing to the coupling of mechanical and mass-transport properties in conventional scaffolds that lead to poor control towards favorable modulus and permeability combinations.Herein,inspired by the microstructure of natural sea urchin spines,biomimetic scaffolds constructed by pentamode metamaterials(PMs)with hierarchical structural tunability were additively manufactured via selective laser melting.The mechanical and mass-transport properties of scaffolds could be simultaneously tuned by the graded porosity(B/T ratio)and the tapering level(D/d ratio).Compared with traditional metallic biomaterials,our biomimetic PM scaffolds possess graded pore distribution,suitable strength,and significant improvements to cell seeding efficiency,permeability,and impact-tolerant capacity,and they also promote in vivo osteogenesis,indicating promising application for cell proliferation and bone regeneration using a structural innovation.展开更多
五零能模式材料是一种新型人工超材料,特征为其弹性模量矩阵的6个特征值中5个为零,可用等效体积模量来描述,表现出类似流体的性质,可被应用于声学隐声斗篷的设计中.然而,根据Norris A N[1]提出的理论,设计五零能模式材料时,与应用变换...五零能模式材料是一种新型人工超材料,特征为其弹性模量矩阵的6个特征值中5个为零,可用等效体积模量来描述,表现出类似流体的性质,可被应用于声学隐声斗篷的设计中.然而,根据Norris A N[1]提出的理论,设计五零能模式材料时,与应用变换声学方法设计一般声学人工超材料不同,要求其满足一非线性偏微分方程约束.论文利用非线性有限元的完全拉格朗日方法,推导了这一偏微分方程的弱形式,并给出了相应的非线性有限元计算列式,以及迭代求解的具体算法.最后,给出了五零能摸式材料设计的二维和三维坐标变换数值算例.展开更多
文摘Metamaterials have been receiving an increasing amount of interest in recent years. As a type of metamaterial, pentamode materials (PMs) approximate the elastic properties of liquids. In this study, a finite-element analysis was conducted to predict the mechanical properties of PM structures by altering the thin wall thicknesses and layer numbers to obtain an outstanding load-bearing capacity. It was found that as the thin wall thickness increased from 0.15 to 0.45 mm, the compressive modulus of the PM structures increased and the Poisson’s ratio decreased. As the layer number increased, the Poisson’s ratio of the PM structures increased rapidly and reaches a stable value ranging from 0.50 to 0.55. Simulation results of the stress distribution in the PM structures confirmed that stress concentrations exist at the junctions of the thin walls and weights. For validation, Ti–6Al–4V specimens were fabricated by selective laser melting (SLM), and the mechanical properties of these specimens (i.e., Poisson’s ratio and elastic modulus) were experimentally studied. Good consistency was achieved between the numerical and experimental results. This work is beneficial for the design and development of PM structures with simultaneous load-bearing capacity and pentamodal properties.
文摘<div style="text-align:justify;"> Coding metasurface draws amounts of research interests due to its potential for achieving sophisticated functions in wave manipulation by using simple logical unit cells with out-of-phase responses. In this paper, we present a novel acoustic coding metasurface structure for underwater sound scattering reduction based on pentamode metamaterials. The metasurface is composed of two types of hexagonal pentamode unit cells with phase responses of 0 and π respectively. The units are arranged in random 1-bit coding sequence to achieve low-scattering underwater acoustic stealth effect. Full-wave simulation results are in good accordance with the theoretical expectation. The optimized arrangement resulted in the distribution of scattered underwater acoustic waves and suppression of the far field scattering coefficient over a wide range of incident angles. We show that pentamode-based coding metasurface provides an efficient scheme to achieve underwater acoustic stealth by ultrathin structures. </div>
基金This work was sponsored by the National Natural Science Foundation of China(Grant No.51922044)the Key Area Research and Development Program of Guangdong Province(No.2020B090923001)the Academic frontier youth team at Huazhong University of Science and Technology(HUST)(2018QYTD04).
文摘Biomimetic metallic biomaterials prepared for bone scaffolds have drawn more and more attention in recent years.However,the topological design of scaffolds is critical to cater to multi-physical requirements for efficient cell seeding and bone regeneration,yet remains a big scientific challenge owing to the coupling of mechanical and mass-transport properties in conventional scaffolds that lead to poor control towards favorable modulus and permeability combinations.Herein,inspired by the microstructure of natural sea urchin spines,biomimetic scaffolds constructed by pentamode metamaterials(PMs)with hierarchical structural tunability were additively manufactured via selective laser melting.The mechanical and mass-transport properties of scaffolds could be simultaneously tuned by the graded porosity(B/T ratio)and the tapering level(D/d ratio).Compared with traditional metallic biomaterials,our biomimetic PM scaffolds possess graded pore distribution,suitable strength,and significant improvements to cell seeding efficiency,permeability,and impact-tolerant capacity,and they also promote in vivo osteogenesis,indicating promising application for cell proliferation and bone regeneration using a structural innovation.
文摘五零能模式材料是一种新型人工超材料,特征为其弹性模量矩阵的6个特征值中5个为零,可用等效体积模量来描述,表现出类似流体的性质,可被应用于声学隐声斗篷的设计中.然而,根据Norris A N[1]提出的理论,设计五零能模式材料时,与应用变换声学方法设计一般声学人工超材料不同,要求其满足一非线性偏微分方程约束.论文利用非线性有限元的完全拉格朗日方法,推导了这一偏微分方程的弱形式,并给出了相应的非线性有限元计算列式,以及迭代求解的具体算法.最后,给出了五零能摸式材料设计的二维和三维坐标变换数值算例.
