泡沫金属中池沸腾传热的研究进展

介绍了泡沫金属的结构特性,总结了泡沫金属中池沸腾的气泡生长速度、气泡直径和气泡生长现象等传热特点,以及泡沫金属的孔隙率、孔密度等参数对池沸腾传热的影响,并指出了泡沫金属中沸腾传热的研究方向。     

Bestow metal foams with nanostructured surfaces via a convenient electrochemical method for improved device performance

Metal foams have been intensively studied as three-dimensional (3-D) bulk mass-support for various applications because of their high conductivities and attractive mechanical properties.However,the relatively low surface area of conventional metal foams largely limits their performance in applications such as charge storage.Here,we present a convenient electrochemical method for addressing this problem using Cu foams as an example.High surface area Cu foams are fabricated in a one-pot one-step manner by repetitive electrodeposition and dealloying treatments.The obtained Cu foams exhibit greatly improved performance for different applications like surface enhanced Raman spectroscopy (SERS) substrates and 3-D bulk supercapacitor electrodes.     

Cellular Metals Manufacturing

Open cell, stochastic nickel foams are widely used for the electrodes and current collectors of metal – metal hydride batteries. Closed cell, periodic aluminum honeycomb is extensively used for the cores of light, stiff sandwich panel structures. Interest is now growing in other cell topologies and potential applications are expanding. For example cellular metals are being evaluated for impact energy absorption, for noise and vibration damping and for novel approaches to thermal management. Numerous methods for manufacturing cellular metals are being developed. As a basic understanding of the relationships between cell topology and the performance of cellular metals in each application area begins to emerge, interest is growing in processes that enable an optimized topology to be reproducibly created. For some applications, such as acoustic attenuation, stochastic metal foams are likely to be preferred over their periodically structured counterparts. Nonetheless, the average cell s ize, the cell size standard deviation, the relative density and the microstructure of the ligaments are all important to control. The invention of more stable processes and improved methods for on‐line control of the cellular structure via in‐situ sensing and more sophisticated control algorithms are likely to lead to significant improvements in foam topology. For load supporting applications, sandwich panels containing honeycomb cores are much superior to those utilizing stochastic foams, but they are more costly than stochastic foam core materials. Recently, processes have begun to emerge for making open cell periodic cell materials with triangular or pyramidal truss topologies. These have been shown to match the stiffness and strength of honeycomb in sandwich panels. New cellular metals manufacturing processes that use metal textiles and deformed sheet metal are being explored as potentially low cost manufacturing processes for these applications. These topologically optimized systems are opening up new multifunctional applications for cellular metals.     

Nonlinear behavior of bumper foams under uniaxial compressive cyclic loading

Theoretical and experimental studies on the nonlinear behaviors of bumper foams under cyclic loading are carried out in this paper. To study the compressible materials, the incompressible viscoelastic model proposed by Rajagopal and Srinivasa in 2000 is modified and expressed as a function of the principal stretches. The modified model is used to describe bumper foams for the first time. Besides, in order to better predict the nonlinear process of bumper foams under cyclic loading, a new compressible viscoplastic model is proposed, which is expressed separately as the invariants of stretches and the principal stretches. Then the compressible viscoelastic model and the compressible viscoplastic model are used to describe the response of bumper foams under cyclic loading with constant and variable amplitudes, respectively. The experimental results demonstrate that the compressible viscoelastic model and the compressible viscoplastic model are both suitable to describe the response of bumper foams under cyclic loading, the new proposed compressible viscoplastic model is more suitable to describe the deformation at the end of each cycle.     

Comparison of tensile and compressive characteristics of vinyl ester/glass microballoon syntactic foams

The present study is focused on the synthesis and characterization of vinyl ester/glass microballoon syntactic foams. Tensile and compressive properties of vinyl ester matrix syntactic foams are characterized. Results show that the compressive strength and moduli of several syntactic foam compositions are comparable to those of the neat matrix resin. Due to the lower density of syntactic foams, the specific compressive properties of all compositions are higher than those of the neat resin. Similar trends are observed in the tensile properties. Mechanical properties of vinyl ester matrix syntactic foams are compared to well-documented mechanical properties of epoxy matrix systems. The comparison shows that low cost vinyl ester resins, which are extensively used in marine applications, can result in syntactic foams with comparable performance to epoxy matrix systems. In addition, tensile modulus is found to be 15–30% higher than the compressive modulus for all syntactic foam compositions. This difference is related to the possibility of particle fracture in the stress range where modulus is calculated in the compressive stress–strain curves.     

A comparison of composite metal foam's properties and other comparable metal foams

New closed cell composite metal foams are processed using casting and powder metallurgy (PM) techniques. The foam is comprised of steel hollow spheres packed into a random loose arrangement, with the interstitial spaces between spheres occupied with a solid metallic matrix. The characterization of composite metal foams was carried out using monotonic compression, compression-compression fatigue, loading-unloading compression, micro-hardness and nano-hardness testing. The microstructure of the composite metal foams was studied using optical, scanning electron microscopy imaging and electron dispersive spectroscopy. The composite metal foams displayed superior (5-20 times higher) compressive strengths, reported as 105 MPa for cast foams and 127 MPa for PM foams, and much higher energy absorbing capability as compared to other metal foams being produced with similar materials through other technologies.     

金属泡沫材料研究进展

综述了金属泡沫材料的各种制备方法。液相法制备金属泡沫材料包括气体吹入法、固体发泡剂法和固体—气体共晶凝固法、熔模铸造法、渗流铸造法、喷射沉积法以及粉末加压熔化法等制备方法。采用金属粉末烧结法、浆料发泡法等制备工艺可以从固相制备金属泡沫材料。电沉积法以及气相沉积法可用于制备高孔隙率的金属泡沫材料。最后简要总结了金属泡沫材料的应用。     

High-frequency tortuosity relaxation in open-cell foams

Propagation of ultrasounds through open-cell polymeric foams is studied using air-coupled ultrasound and Fourier spectral analysis (both phase and magnitude) in the frequency range 0.1 to 6 MHz. A detailed micrographic study is first performed to determine struts dimensions and cell geometry, hence, a unit cell model to describe these foams is proposed. Ultrasound phase velocity and transmission loss were then measured. Variation of these magnitudes with the frequency follows the shape of a sigmoid growth. This behavior of the phase velocity can be explained by introducing an apparent tortuosity with a relaxation-like behavior, which can be explained by considering a probabilistic tortuous walk, as it has recently been performed for other kind of foams. However and unlike in previous studies, the present one shows the whole transition of this sigmoid growth for all studied foams. This is achieved by a precise selection of the foam samples and by the fabrication of new air-coupled transducers that enlarge the experimental working frequency range to lower frequencies. The study of the measured sigmoid growth is used to determine the probability function, required by the probabilistic tortuous walk model, which best describes the variation of the apparent tortuosity.     

软硬交错金属空心球泡沫动力学性能研究

通过控制点阵结构中不同阵点位置空心球的软硬程度建立了交错金属空心球泡沫模型。在此基础上,对比研究了不同冲击条件下,均匀和各种交错金属空心球泡沫的动力学响应特性。重点分析了软硬空心球排布方式对金属空心球泡沫动力学性能的影响。研究结果表明,通过对软硬空心球排布方式的控制,材料可以在一定范围内根据外载条件进行自主调节,以控制金属空心球泡沫内的应力分布,提高了金属空心球泡沫的能量吸收效率。软硬交错空心球模型的建立为实现金属空心球泡沫的自适应设计提供了新的思路。     

Strain-rate effects in Ni/Al composite metal foams from quasi-static to low-velocity impact behaviour

Metal foams are used as absorbers for kinetic energy but predominantly, they have only been investigated under quasi-static load-conditions. Coating of open-cell metal foams improves the mechanical properties by forming of Ni/Al hybrid foam composites. The properties are governed by the microstructure, the strut material and geometry. In this study, the strain-rate effects in open-cell aluminium foams and new Ni/Al composite foams are investigated by quasi-static compression tests and low-velocity impact. For the first time, drop weight tests are reported on open-cell metal foams, especially Ni/Al composite foams. Furthermore, size-effects were evaluated. The microstructural deformation mechanism was analysed using a high-speed camera and digital image correlation. Whereas pure aluminium foams are only strain-rate sensitive in the plastic collapse stress, Ni/Al foams show a general strain-rate sensitivity based on microinertia effects and the rate-sensitive nano-nickel coating. Ni/Al foams are superior to aluminium foams and to artificial aluminium foams with equal density.     

Si元素对碳纳米管增强铝基复合泡沫组织与性能的影响

针对金属基复合材料,添加合金元素是提升其综合性能的有效途径.本文通过高能球磨和填加造孔剂法,制备了添加Si元素的碳纳米管(CNTs)增强铝基(CNTs/Al-Si)复合泡沫,通过准静态压缩实验测试其压缩性能和吸能性能,进一步研究烧结温度和不同Si元素含量对CNTs/Al-Si复合泡沫微观组织、压缩性能和吸能性能的影响,...     

Facile fabrication of core-shell Ni_3Se_2/Ni nanofoams composites for lithium ion battery anodes

Due to the highly porous structure, large specific surface area, and 3 D interconnected metal conductive network, nanoporous metal foams have attracted a lot of attention in the field of energy conversion and storage, especially lithium-ion batteries, which are ideal for current collectors. In this work, we develop a facile approach to fabricate core-shell Ni_3Se_2/Ni nanofoams composites. The Ni_3Se_2/Ni composites make full use of both the advantages of metal conductive network and core-shell structure, resulting in a high capacity and superior rate performance. In addition, the composites can be directly converted into electrode by a simple mechanical compression, which is more convenient than traditional casting method. What's more, this material and its structure can be extended to other devices in the field of energy conversion and storage.     

泡沫铝连接件焊接工艺的应用现状与展望

泡沫铝兼具结构与功能特性,为充分发挥泡沫铝的各种性能,常将其与致密金属进行复合得到三明治结构,以提高其综合力学性能并降低成本。三明治结构的连接方法众多,而焊接手段是最可靠的连接方式。首先介绍了泡沫铝的性能特点及焊接难点,综述了其焊接方法,包括常规电弧焊、激光焊、钎焊、扩散焊、搅拌摩擦焊、等离子焊以及超声波焊,再对各工艺的局限性进行阐述,最后对泡沫铝连接件焊接工艺的发展方向进行浅析。     

A Powder Metallurgic Approach toward High‐Performance Lithium Metal Anodes

The development of lithium metal anodes capable of sustaining large volume changes, avoiding lithium dendrite formation, and remaining stable in ambient air is crucial for commercially viable lithium metal batteries. Toward this goal, the fabrication of porous and lithiophilic copper scaffolds via a powder metallurgy strategy is reported. Infiltrating the scaffolds with molten lithium followed by exposure to Freon R134a produces lithium metal anodes with dramatically improved rate performance and cycling stability. This work provides a simple yet effective route for the fabrication of safe, low‐cost lithium metal batteries with high energy density.     

Metal foaming by a powder metallurgy method: Production, properties and applications

 A method for fabricating metal foams based on the powder metallurgy process is presented. This foaming process allows for the production of complex-shaped foam parts, metal foam sandwich panels and foam filled hollow profiles. A range of alloys can be foamed using this method including aluminum, zinc, tin, lead and steel. The as-produced part has a closed-cell microstructure and a high fraction of porosity (typical range from 40–90% porosity). Selected mechanical properties of metal foams are evaluated, including the loading of foam samples with and without face skins and the axial crushing of tubular structures with foam reinforcement. Potential applications are discussed such as light-weight construction and energy absorption for both military and civilian uses. Received: 22 July 1998 / Accepted: 4 September 1998     

Aluminium foams for transport industry

Foamed materials are widespread in transportation industry applications. While polymeric foams have been applied for many years foamed metals are now beginning to move into the focus of interest. A powder metallurgical method which allows the production of aluminium foams with porosity levels up to 90% is described. The foams typically have closed pores and densities ranging from 0.4 to 1 g cm⁻³, so that this foamed metals float on water. The unique mechanical properties of metal foams are described. The density dependence of metal foam properties is shown with the Young's modulus, flexural strength and compression strength as examples. A non-linear dependency of these properties on the density is found and discussed. The discussion then focuses on the energy absorption properties of aluminium foams and tools to select appropriate foams for a given energy absorption task.     

Correlation between Elastic and Electric Properties for Metal Foams: Theory and Experiment

Correlation between Young's modulus and electric conductivity is given in the explicit form for metal foams. Theoretical predictions are compared with the experimental measurements for AlMg1Si0.6 aluminum foams with porosity in the range 70 to 90%. The agreement is better than 10% in all cases.     

泡沫金属的制备工艺及应用

根据泡沫金属制备过程中金属的状态,将泡沫金属的制备方法归类为:熔体凝固法、固态烧结法、金属沉积法,并按此分类对泡沫金属常用制备工艺进行了介绍.泡沫金属具有轻质、高孔隙率、电磁屏蔽等性能,按照功能用途和结构用途2方面对其应用领域进行了介绍.     

Comparison between RVE and full mesh approaches for the simulation of compression tests on cellular metals

Metal foams are materials of recent development and application that show interesting combinations of physical and mechanical properties. Many applications are envisaged for such materials, particularly in equipments of passive safety, because of their high capacity of energy absorption under impact conditions. The damage analysis in metallic foams is a complex problem and must be performed in a finite strain context. Considering that compression is the dominant loading in impact situations, a finite deformation simulation including damage effects of a compression test on a cellular metal sample is shown in this work. The main objective of the paper is to compare simulations considering periodic boundary conditions, by means of a representative volume element (RVE) approach, with results obtained using full meshes. It is shown that, when the imposed deformation is high, the use of RVE does not describe in a proper manner the deformation that occurs at the walls of cells. This characteristic of RVE approach results in a too stiff behavior when considering load‐displacement relations. A comparison with experimental results is also presented.