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Some topics on elastic metamaterials

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Acta Mechanica Sinica 2023年第7期39卷 1-2页

作者： gengkai hu Guoliang huang School of Aerospace Engineering Beijing Institute of TechnologyBeijing 100081China Department of Mechanical and Aerospace Engineering University of MissouriColumbia MO 65211USA

Acoustic metamaterials are composite materials that exhibit effective material properties beyond those of their constituent *** engineering negative properties,such as modulus,mass density,refractive index,and thermal expansion coefficient from positive constituents,these materials offer a range of mechanical and acoustic properties,as well as transport and stimuli-responsive *** mitigation and vibration suppression are popular applications of acoustic metamaterials,with band gap formation and artificial damping being the primary *** research has also leveraged the principles of topological insulators in electronics and photonics to realize phononic topological phases,leading to robust mechanical boundary modes that are resistant to defects and geometric ***,the emergence of acoustic nonreciprocity has led to new wave-related strategies such as acoustic diodes,unidirectional invisibility,and autonomous robots.

关键词： visibility unidirectional modulus

In-Plane Semi-Linear Cloaks with Arbitrary Shape

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Acta Mechanica Solida Sinica 2019年第3期32卷 277-286页

作者： Dengke Guo Zheng Chang gengkai hu Key Laboratory of Dynamics and Control of Flight Vehicle Ministry of Education School of Aerospace Engineering Beijing Institute of Technology Beijing 100081 China College of Science China Agricultural University Beijing 100083 China

Soft materials with semi-linear strain energy function can be used as smart transformation media to manipulate elastic waves via finite pre-deformation. However, the intrinsic cons train ts involved in such materials limit the shapes of t ransformation devices to very sim - pie cases. In this work, combining theoretical and numerical analyses, we report an approach of achieving the in-plane elastodynamic cloak with arbitrary shape. We demonstrate that with the appropriate out-of^plane st retch applied on the semi-linear material, cloaking effec t can be achieved for both P- and SV-waves in the symmetrie plane of a 3D domain, and the performance of the cloak with arbitrary cross section can be guaranteed for relatively small in-plane rot at ion. In addition, we propose an empirical formula to predic t the deformation limit of the cloaks with semi-linear materials. This work may stimulate the experimental research on softmatter- based transformation devices. Potential applications can be anticipated in nondestructive testing, structure impact protection, biomedical imaging and soft robotics.

关键词： Elastic waves Cloak Hyperelasticity Semi-linear Arbitrary shape

HEAT FLOW CONTROL BY TRANSFORMATION METHOD WITH GRID GENERATION METHOD

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Acta Mechanica Solida Sinica 2014年第5期27卷 454-460页

作者： Zheng Chang Xiaoning Liu gengkai hu Key Laboratory of Dynamics and Control of Flight Vehicle Ministry of Education School of Aerospace Engineering Beijing Institute of Technology CNMM & AML Department of Engineering Mechanics Tsinghua University

In the context of the transformation method, we propose a general approach to construct numerically the mapping generated by imposing specific boundary conditions with a targeted function, and the necessary material and heat source spatial distributions are then derived with the help of transformation method. The construction of mapping by grid generation method through solving partial differential equations circumvents the limitation of device geometry, which paves the way for designing more complex heat flow control devices. Two numerical examples are also given to show how to design material properties and heat source in order to control temperature patterns.

关键词： heat conduction inverse problem transformation method grid generation

Underwater Directional Acoustic Source Based on Pentamode Material

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Acta Mechanica Solida Sinica 2024年第1期37卷 1-9页

作者： Binghao Zhao Peng Wang Dongwei Wang gengkai hu School of Aerospace Engineering Beijing Institute of TechnologyBeijing 100081China Wuhan Second Ship Design and Research Institute Wuhan 430205China

An underwater directional acoustic emitter is conceived with a highly anisotropic lattice material,whose acoustic characteristics manifest strong dependence on the orientation of the lattice material’s principal *** these features,a cylindrical structure made of such anisotropic lattice material is engineered to possess distinct impedance values in different directions,thereby facilitating wave emission along the principal axis while inducing reflection in other ***,through numerical simulations,it is demonstrated that the emission direction can be effectively manipulated by adjusting the principal axis orientation,concurrently enhancing the emitted *** contrast to previous directional acoustic structures,the compact emitter presented in this study can get rid of the size-wavelength constraint,enabling effective control of low-frequency waves.

关键词： Underwater Directional emission Pentamode material Broadband frequency

Design of elliptical underwater acoustic cloak with truss-latticed pentamode materials

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Theoretical & Applied Mechanics Letters 2022年第4期12卷 221-226页

作者： Yuanyuan Ge Xiaoning Liu gengkai hu School of Aerospace Engineering Beijing Institute of TechnologyBeijing 100081China

Pentamode acoustic cloak is promising for underwater sound control due to its solid nature and broadband efficiency,however its realization is only limited to simple cylindrical *** this work,we established a set of techniques for the microstructure design of elliptical pentamode acoustic cloak based on truss lattice model,including the inverse design of unit cell and algorithms for latticed cloak *** designed cloak was numerically validated by the well wave concealing *** work proves that more general pentamode acoustic wave devices beyond simple cylindrical geometry are theoretically feasible,and sheds light on more practical design for waterborne sound manipulation.

关键词： Elliptical acoustic cloak Pentamode material Microstructure design Truss lattice

Mechanism of dust removal by a standing wave electric curtain

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Science China(Physics,Mechanics & Astronomy) 2012年第6期55卷 1018-1025页

作者： SUN QiXia YANG NingNing CAI XiaoBing hu gengkai School of Aerospace Engineering Beijing Institute of TechnologyBeijing 100081China

In this paper,the mechanisms of particle movement on an electric curtain are *** bursts in which particles leaping from a surface of an electric curtain are demonstrated both by numerical simulation and experimental *** hopping and surfing modes during particle removal are shown to depend on the particle electric charge and its initial *** particles initially located on the top of electrode have a large electric charge tend to assume a hopping *** movement of the particle initially located between the electrodes is analyzed,and the particle traps along the electric curtain surface are also observed.

关键词： electrical curtain dust removal dielectrophoresis force particle dynamic simulation

Elastic metamaterials with local resonances:an overview

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Theoretical & Applied Mechanics Letters 2012年第4期2卷 1-12页

作者： Xiaoming Zhou Xiaoning Liu gengkai hu Key Laboratory of Dynamics and Control of Flight Vehicle Ministry of Education and School of AerospaceEngineering Beijing Institute of Technology Beijing 100081 China

Metamaterials are artificial composite materials engineered to have properties that may not be found in nature. By exploring locally resonant effect of the building units, elastic metamaterials are able to possess negative values of effective mass, effective bulk or shear modulus. Mass-spring and continuum material versions of these elastic metamaterials are reported and the physical mechanisms of negative effective parameters are demonstrated. Applications of metamaterials to acoustic cloaking and superlensing are also discussed.

关键词： metamaterials negative mass negative modulus resonance cloaking superlensing

Acoustic cloak constructed with thin-plate metamaterials

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International Journal of Smart and Nano Materials 2015年第1期6卷 73-83页

作者： Pei Li Xuebing Chen Xiaoming Zhou gengkai hu Ping Xiang Key Laboratory of Dynamics and Control of Flight Vehicle Ministry of Educationand School of Aerospace EngineeringBeijing Institute of Technology100081BeijingChina Systems Engineering Research Institute 100036BeijingChina

We propose a strategy for designing the cylindrical acoustic cloak with thin-plate *** inhomogeneous cloaking shell as derived by transformation acoustics is first discretized into a three-layer anisotropic metafluid,and their material parameters are optimized by minimizing the external *** these metafluids are practically realized by thin-plate structures according to the metamaterial *** an example,an acoustic cloak is designed with nine layers of thin plate and totally 900 plate *** simulations are performed to assess the cloaking performance of the designed structure.

关键词： acoustic cloak thin-plate metamaterial optimization

γ-TiAl基PST晶体的屈服应力及孪晶影响的细观力学研究

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金属学报 2005年第12期41卷 1243-1248页

作者：苏继龙胡更开福建农林大学机电工程系福州350002 北京理工大学应用力学系北京100081

基于γ-TiAl基PST晶体的微结构及滑移系和形变孪晶的空间晶体学位向分布的变形机制,提出了分析PST晶体屈服应力对外载轴和片层界面夹角θ间的依赖关系的细观力学解析模型,重点考察了PST晶体的微结构和普通位错与形变孪晶的临界分切应... 详细信息

基于γ-TiAl基PST晶体的微结构及滑移系和形变孪晶的空间晶体学位向分布的变形机制,提出了分析PST晶体屈服应力对外载轴和片层界面夹角θ间的依赖关系的细观力学解析模型,重点考察了PST晶体的微结构和普通位错与形变孪晶的临界分切应力(CRSS)之闻的差别对晶体屈服的影响．结果表明: PST晶体屈服应力σy和外载轴与片层界面之间的夹角θ 存在着强烈依赖关系．在软取向,变形由普通位错和超位错控制,变形平行于片层界面;而在硬取向,变形由形变孪晶控制,PST 晶体的变形为穿过片层界面形式．在加载角θ分别为45°,0°和90°时,屈服应力间的关系为: σy(45°)<σy(0°)<σy(90°)．同时,分析了滑移系和形变孪晶的具体开动情况．

关键词： γ-TiAl基合金 PST晶体滑移系屈服应力细观力学