超轻多孔金属材料的多功能特性及应用

超轻多孔金属是近年来随着多样化需求的材料制备以及机械加工技术的迅速发展而出现的一 类新颖多功能材料, 是材料的选择及其性能研究的新课题. 本文介绍有关多孔金属材料与结 构基础研究的国内外研究现状和发展趋势, 涉及材料制备、性能表征等方面, 着重于探讨多 孔金属的多功能复合特性及其在国民经济和高技术中的应用.     

多孔金属及其夹芯结构力学性能的研究进展

高孔隙率多孔金属及其夹芯复合结构是一种物理功能与结构一体化的新型、轻质高强材料/结构,具有高比强度、高比刚度和优良的吸能和缓冲性能等多种功能,引起了学术界和工程界众多研究者的极大关注. 本文概述了轻质多孔金属及其夹芯结构的制备方法、多功能特性及其应用,介绍了多孔金属夹芯结构元件(梁、板、壳)遭受准静态和动态冲击载荷下的理论、实验和模拟方面的国内外研究现状,分析和讨论了多孔金属及其夹芯结构力学行为研究中的研究手段和基本问题,重点关注了多孔金属夹芯结构的变形/失效、动态响应和能量吸收.     

SOUND ABSORBING PROPERTY OF POROUS METAL MATERIAL AT HIGH TEMPERATURE AND HIGH SOUND PRESSURE LEVEL

在多孔金属材料的湍流统计理论的基础之上, 考虑温度高声压对多孔材料声学参数的影响, 得到适用于高温高声压条件下多孔金属材料的分析模型. 计算了不同温度和不同声压级条件下声压幅值与金属纤维直径、孔隙率等物理参数的关系. 研究发现其他参数不变, 在高温条件下, 随温度升高多孔金属材料的声压幅值增大; 在高声压条件下, 随着声压的升高多孔金属材料的声压幅值增大. 所得理论结果与已有的实验中的规律符合良好,为多孔金属材料在高温、高声压条件下的减振降噪设计提供了理论基础.     

轻质多孔夹芯结构的弹道侵彻行为研究进展

多孔夹芯结构是一类由薄而刚硬的面板和多孔材料芯材构成的复合结构,具有高比刚度、高比强度、缓冲吸能效果优异、可设计性强等特性,在航空航天、交通运输、结构防护等诸多领域引起了广泛关注,且已有诸多成功的工程应用案例,是一类极具潜力的先进轻质高强多功能一体化结构.为阐明轻质多孔夹芯结构的抗侵彻特性与耗能机理,进一步拓展轻质多孔夹芯结构的工程应用范围,对轻质多孔夹芯结构弹道侵彻行为的研究成果进行了系统的综述和展望,依据轻质多孔夹芯结构的结构特征及类型,分别评述了不同类型多孔夹芯结构的抗弹道侵彻破坏机制、能量耗散机理及轻量化设计等方面的研究,展望了未来多孔夹芯结构在抗弹道侵彻研究领域面临的问题和挑战.     

封面图片说明

正封面图为某款防雷车(右上图)以及用于轻质防雷底板的超轻多孔金属材料结构的主要特征.上侧左图是孔形貌呈无序分布的泡沫金属材料,可选作低当量地雷防护设计材料;中间图是孔形貌呈有序分布的点阵金属材料(包括三维和二维),是性能优良的结构承载材料,可选作中型当量地雷防护设计材料;下图是多孔金属复合材料,典型的有波纹-泡沫铝复合、金字塔-陶瓷复合等,可选作较高当量地雷防护设计材料.(图     

力学与实践第30卷（2008年）总目次

综述..…卢天健刘涛邓子辰‘1.1 ................……程昌钧(1.10 1.11 11 nU︸a刁己从1上9 11，l又注泣注注生生丘5.住注(9曰(q口n八(((((门匕了l了l几l了l多孔金属材料多功能化设计的若干进展..…，...........……理性力学在中国的传播与发展...........……，........……     

基于表面效应三维纳米多孔金属力学性能的有限元分析

纳米多孔金属是一类包含大量纳米尺度孔洞的金属材料,孔洞突出的表面效应,使得其具有比传统多孔金属更为优异的力学性能.相对于理论和分子动力学仿真,有限元方法更适用于复杂结构模型,但受限于理论难度,以往研究仍将纳米多孔金属模型简化为较为简单的二维结构,因此无法真实刻画纳米多孔金属的力学性能.为此,基于Gurtin-Murdoch表面理论,成功构建计入纳米表面效应的有限元表面单元,并考虑微观结构非均匀性,发展面向一般三维纳米多孔金属力学行为的有限元计算模型,将计算得到的纳米孔附近应力分布与参考文献进行对比分析,验证了所构建有限元模型的有效性.通过对包含单球孔和随机多球孔的纳米多孔金属进行单轴拉伸和单轴压缩模拟,揭示了孔隙率、孔洞数量和表面参数对纳米多孔金属杨氏模量、压缩屈服强度和吸能性的影响规律.结果表明:所构建的有限元模型可准确捕捉纳米孔附近应力分布,相对于表面拉梅常数,纳米多孔金属的杨氏模量显著依赖于孔洞表面残余应力和加载方向.所构建的有限元模型为纳米多孔金属力学性能预测提供科学依据.     

多功能含能结构材料冲击压缩特性的理论计算

基于混合物冷能叠加原理,由各组分Hugoniot数据计算了密实材料的冲击压缩特性。再从等压 路径出发,结合Wu-Jing模型由热力学关系得到了具有一定孔隙率多功能含能结构材料的冲击压缩特性计算 方法。以W/Cu、Al/Ni、Ni/Ti和Al/Fe2O3/epoxy等典型颗粒金属材料及含能金属材料为例,计算了其冲击 压缩过程中相关Hugoniot参数。计算结果与已有实验结果吻合较好,多功能含能结构材料冲击压缩特性受 材料孔隙率、材料配比等影响明显。     

轻质波纹夹层结构的制备及其多功能应用研究进展

波纹夹层结构较其他轻质多孔材料具有结构简单、加工制造方便、制造成本低等优点,已得到广泛应用.本文概述了不同轻质波纹结构的构型及其表征方式,阐述了波纹夹层结构的制备及其无损检测技术,重点评述了波纹夹层结构的轻质高强、抗爆炸冲击、高效散热、吸声降噪、促动等多功能应用特性,总结了波纹夹层结构在工程应用上的关键进展,展望了波纹夹层结构在基础和应用研究方面的发展趋势.     

高温条件下纤维型多孔金属材料声振耦合的研究

以高温条件下纤维型多孔金属材料声振耦合为研究目的,在研究温度与多孔材料声学参数之间关系的基础上,将Biot多孔材料声-固耦合理论拓展到高温条件下。从理论上分析了声波与多孔材料在高温条件下的耦合状况,并将理论分析结果与实验数据进行了比较,表明了该理论分析的合理性。     

Two-dimensional cellular metals as multifunctional structures: topology optimization

Highly porous two-dimensional (2D) cellular metals have multifunctional attributes, with tailorable structures to achieve multifunctional performance. The focus of this study is to explore the optimal cellular topology of 2D cellular metals for heat dissipation, and to investigate the eligibility of different heat enhancement techniques for more efficient heat dissipation. An analytical approach for the optimal design of metallic 2D cellular materials, cooled by single-phase laminar forced convection in various flow configurations, is proposed and validated by comparison with full numerical simulations. The optimal design is characterized by two subsidiary dimensionless parameters: one reflecting the trade-off between convection and fluid friction, and the other reflecting the optimal balance between conduction and convection. A heat transfer enhancement technique––boundary layer redevelopment––is subsequently introduced and its feasibility examined experimentally. Future research directions in specific areas are discussed.     

Multifunctional design of two-dimensional cellular materials with tailored mesostructure

Two-dimensional cellular materials (prismatic honeycombs) provide a range of properties that make them suitable for multifunctional applications involving heat dissipation and structural performance. In this paper we present two-scale homogenization-based finite element scheme for convective heat transfer and structural characterization of 2-D cellular metals with uniform and graded cell sizes of various topologies as well as with mixed cell-topologies. For convective heat transfer analysis, the cells are modeled implicitly as temperature-dependent sinks modeling the out-of-plane fluid convection through the cells; the sink strength is determined via a micromechanics problem of heat transfer in a cell. For structural analysis, the cellular material is represented as a micropolar continuum with linear elastic constitutive equations obtained via micromechanics solution of a representative unit cell. The analyses are then used in conjunction with an optimization algorithm to design cellular materials with functionally tailored mesostructures. The analysis and design framework enables tailoring cellular materials with graded cell structures of a given topology as well as with cell structures that combine multiple topologies.     

多功能室温液态金属在不同摩擦副条件下的润滑性能研究

室温液态金属是一类物理化学行为非常独特的新型功能物质,其诸多性能和用途尚未可知.本论文中初步探索了Ga_(75.5)In_(24.5)和Ga_(65)In_(22)Sn_(13)两种液态金属润滑特性与摩擦配副选材间的关系.结果表明:镓基液态金属在钢及陶瓷表面的润湿性能不佳,接触角大于120°.采用AISI 52100钢和陶瓷配副时,镓基液态金属表现出良好的润滑特性和极佳的承压能力;采用AISI 52100钢自配副时,镓基液态金属的减摩效应不明显,但能较大幅度降低材料的磨损率;采用陶瓷-陶瓷配副时,镓基液态金属几乎没有润滑作用.镓基液态金属润滑特性差异与其在材料表面的摩擦化学反应有关.     

On an elastic-plastic transition zone in cellular metals

Summary A theory of plasticity is proposed for cellular metals to describe their elastic-plastic transition zone at small strain. Under certain conditions, only a plane strain test is necessary to determine the yield surface. The method to derive the elastic–plastic behaviour [14, 15] was originally proposed for classical metals. A simple cubic model of a cellular metal is used to demonstrate the method by the finite element method. Recommendations for the numerical simulation are given. The influence of the relative density and the hardening behaviour of the cell wall material is investigated.     

The microstructural origin of strain hardening in two-dimensional open-cell metal foams

This paper aims at elucidating the microstructural origin of strain hardening in open-cell metal foams. We have developed a multiscale model that allows to study the development of plasticity at two length scales: (i) the development of plastic zones inside individual struts (microscopic scale) and (ii) the formation of plastic localization bands at the scale of the cellular architecture (mesoscopic scale). We address how plasticity at both scales contribute to the macroscopic yielding and strain hardening of cellular metals. One of the important results is that, in contrast to strain hardening in dense metals, strain hardening in cellular metals consist of a synergistic contribution of two sources: (i) strain hardening of the solid material (microscopic scale) and (ii) geometric hardening due to strut reorientation (mesoscopic scale). We show that the synergy of the two leads to an enhanced macroscopic hardening capacity. Our results are in qualitative agreement with experimental studies and elucidate the microstructural origin of plastic hardening in this class of materials.     

Crashworthiness design of density-graded cellular metals

Crashworthiness of cellular metals with a linear density gradient was analyzed by using cell-based finite element models and shock models. Mechanisms of energy absorption and deformation of graded cellular metals were explored by shock wave propagation analysis. Results show that a positive density gradient is a good choice for protecting the impacting object because it can meet the crashworthiness requirements of high energy absorption, stable impact resistance and low peak stress.     

A numerical study on the rate sensitivity of cellular metals

Metallic foams have non-linear deformation behavior, which make them attractive in many applications. Many experimental researches on the dynamic behavior and rate sensitivity of cellular metals have been reported in the literature, but they contain conflicting, and sometimes confusing, conclusions on the strain-rate and inertia effect of cellular metals. In this paper, the dynamic crushing behavior of 2D Voronoi honeycomb is studied by finite element method. The influences of inertia, strain hardening and strain-rate hardening of metal matrix on the deformation mode and plateau stress of the honeycomb are investigated. Three deformation modes are found in different velocity ranges. According to the numerical results, it is found that the plateau stress increases significantly with the increase of impact velocity due to non-uniform deformation induced by inertia. The strain-hardening effect is slight in our numerical tests and the rate effect of the honeycomb is obviously weaker than that of the cell wall material.     

On the uniaxial compression behavior of regular shaped cellular metals

The numerical simulation of random cellular metals is still connected to many unsolved problems due to their stochastic structure. Therefore, a periodic model of a cellular metal is developed for fundamental studies of the mechanical behavior and is numerically investigated under uniaxial compression. The influence of differing hardening behaviors and differing boundary conditions on the characteristics of the material is investigated. Recommendations for the numerical simulation are derived. In contrast to common models, experimental samples of the same geometry are easy to manufacture and the results of the experiments show good agreement with the finite element calculations. Based on the proposed concept of a unit cell with periodic boundary conditions, it is possible to derive constitutive equations of cellular materials under complex loading conditions.