介质谐振器材料及其应用

本文简要介绍自1970年以来得到重大发展的微波介质谐振器陶瓷,指出某些基本规律、特性及研究发展动向,也讨论了材料特征电参数间的相互依存关系。最后举例说明介质谐振器在蜂巢式便携电话中的双工器及稳频振荡器方面的应用。     

Physical aspects of cell culture substrates: topography, roughness, and elasticity

The cellular environment impacts a myriad of cellular functions by providing signals that can modulate cell phenotype and function. Physical cues such as topography, roughness, gradients, and elasticity are of particular importance. Thus, synthetic substrates can be potentially useful tools for exploring the influence of the aforementioned physical properties on cellular function. Many micro- and nanofabrication processes have been employed to control substrate characteristics in both 2D and 3D environments. This review highlights strategies for modulating the physical properties of surfaces, the influence of these changes on cell responses, and the promise and limitations of these surfaces in in-vitro settings. While both hard and soft materials are discussed, emphasis is placed on soft substrates. Moreover, methods for creating synthetic substrates for cell studies, substrate properties, and impact of substrate properties on cell behavior are the main focus of this review.     

The topological design of multifunctional cellular metals

The multifunctional performance of stochastic (foamed) cellular metals is now well documented. This article compares such materials with the projected capabilities of materials with periodic cells, configured as cores of panels, tubes and shells. The implementation opportunities are as ultra-light structures, for compact cooling, in energy absorption and vibration control. The periodic topologies comprise either micro-truss lattices or prismatic materials. Performance benefits that can be expected upon implementing these periodic materials are presented and compared with competing concepts. Methods for manufacturing these materials are discussed and some cost/performance trade-offs are addressed.     

Global gene expression analysis for evaluation and design of biomaterials

Abstract

Comprehensive gene expression analysis using DNA microarrays has become a widespread technique in molecular biological research. In the biomaterials field, it is used to evaluate the biocompatibility or cellular toxicity of metals, polymers and ceramics. Studies in this field have extracted differentially expressed genes in the context of differences in cellular responses among multiple materials. Based on these genes, the effects of materials on cells at the molecular level have been examined. Expression data ranging from several to tens of thousands of genes can be obtained from DNA microarrays. For this reason, several tens or hundreds of differentially expressed genes are often present in different materials. In this review, we outline the principles of DNA microarrays, and provide an introduction to methods of extracting information which is useful for evaluating and designing biomaterials from comprehensive gene expression data.     

Numerical and experimental design of graded cellular sandwich cores for multi-functional aerospace applications

The present contribution is concerned with a combined experimental and numerical design of graded cellular materials for multifunctional aerospace application performed in the context of an integrated research project funded by the European Commission. The primary objective is an exploration of the potential of functionally graded materials as sandwich cores for multifunctional application. With particulate advanced pore morphology (APM) foams and hollow spheres assemblies, two different types of particle-based cellular base materials are considered. Based on these constituent materials, functionally graded sandwich cores are designed in a combined numerical and experimental approach. Their properties and their performance in the desired application are investigated and optimized. The performance of the optimized material is compared to the performance of a non-graded sandwich core in the numerical simulation of a bird strike experiment.     

Improvement of the mechanical and thermal characteristics of open cell aluminum foams by the electrodeposition of Cu

Recently aluminum foaming has been of much interest due to its characteristics properties of light weight structure. Metallic foams are highly porous materials which present complex structure of three-dimensional open cells. This aspect causes strong limitations in mass transport due to electro-deposition technology. In this work, the electro-deposition of copper on aluminum open-cell foams substrates was developed, in order to enhance the thermal and mechanical properties of these cellular materials. The mechanical and thermal characterization of the produced samples was lead through compression and conductivity tests. On the basis of the experimental results, analytical models are proposed to predict the quantity and the quality characteristics of the coating.     

Experimental analysis of the flexural properties of sandwich panels with cellular core materials

This paper addresses the flexural properties of sandwich structures with cellular core materials. Experimental three point bending tests are conducted in order to determine the flexural stiffness and the load‐carrying capacity of these advanced composites. In addition, the significant failure modes after exceeding the load‐carrying capacity are identified. The results of these analyses are compared for sandwich structures containing various core materials. These core materials comprise two aluminium foams, namely M‐Pore® and Alporas®, honeycomb structures and novel metallic hollow sphere structures (MHSS).     

Nature‐Inspired Lightweight Cellular Co‐Continuous Composites with Architected Periodic Gyroidal Structures

Shell‐core cellular composites are a unique class of cellular materials, where the base constituent is made of a composite material such that the best distinctive physical and/or mechanical properties of each phase of the composite are employed. In this work, the authors demonstrate the additive manufacturing of a nature inspired cellular three‐dimensional (3D), periodic, co‐continuous, and complex composite materials made of a hard‐shell and soft‐core system. The architecture of these composites is based on the Schoen's single Gyroidal triply periodic minimal surface. Results of mechanical testing show the possibility of having a wide range of mechanical properties by tuning the composition, volume fraction of core, shell thickness, and internal architecture of the cellular composites. Moreover, a change in deformation and failure mechanism is observed when employing a shell‐core composite system, as compared to the pure stiff polymeric standalone cellular material. This shell‐core configuration and Gyroidal topology allowed for accessing toughness values that are not realized by the constituent materials independently, showing the suitability of this cellular composite for mechanical energy absorption applications.

     

The correct analysis of shocks in a cellular material

Cellular materials have applications for impact and blast protection. Under impact/impulsive loading the response of the cellular solid can be controlled by compaction (or shock, see Tan et al. (2005) 3 and 4) waves. Different analytical and computational solutions have been produced to model this behaviour but these solutions provide conflicting predictions for the response of the material in certain loading scenarios. The different analytical approaches are discussed using two simple examples for clarity. The differences between apparently similar “models” are clarified. In particular, it is argued that mass-spring models are not capable of modelling the discontinuities that exist in a compaction wave in a cellular material.     

Using Lessons from Cellular and Molecular Structures for Future Materials

Cells and molecules exhibit robust and efficient characteristics that occur as a result of highly organized and hierarchical structures within these small scale living systems. These structures have the ability to adapt themselves to a wide variety of stimuli, including mechanical and chemical environmental changes, which ultimately affect behavior including cell life and death. The characteristics of these structures can be utilized as they provide unique advantages for building a future generation of material science technologies. In this article, we provide an overview of the similarities between materials and living cells, and discuss specific types of biological materials including cytoskeletal elements, DNA, and molecular motors that have already been leveraged to build unique functional materials. The future challenge will be to continue to use the scientific discoveries of today with upcoming discoveries in cellular and molecular science, and apply these principles to develop as yet unknown technologies and materials.     

Conventional and novel processing methods for cellular ceramics

Cellular ceramics are a class of highly porous materials that covers a wide range of structures, such as foams, honeycombs, interconnected rods, interconnected fibres, interconnected hollow spheres. Recently, there has been a surge of activity in this field, because these innovative materials have started to be used as components in special and advanced engineering applications. These include filtering liquids and particles in gas streams, porous burners, biomedical devices, lightweight load-bearing structures, etc. Improvements in conventional processing methods and the development of innovative fabrication approaches are required because of the increasing specific demands on properties and morphology (cell size, size distribution and interconnection) for these materials, which strictly depend on the application considered. This paper will cover the main fabrication methods for cellular ceramics, focusing primarily on foams, offering some insight into novel fabrication processes and recent developments.     

元胞自动机模型方法及其在材料组织结构模拟中的应用

元胞自动机是复杂体系的一种理想化模型 ,它对处理那些难以用数学定量描述的复杂动态体系问题如材料的组织结构演变问题有独到之处 ,并且特别便于计算机模拟实施。本文介绍了元胞自动机的基本思想、分类与特征 ,并综述了元胞自动机模型方法在材料的凝固结晶、再结晶和晶粒长大以及相沉淀和相分解的模拟研究中的应用。     

Topological design of microstructures of cellular materials for maximum bulk or shear modulus

This paper presents a new approach to designing periodic microstructures of cellular materials. The method is based on the bidirectional evolutionary structural optimization (BESO) technique. The optimization problem is formulated as finding a micro-structural topology with the maximum bulk or shear modulus under a prescribed volume constraint. Using the homogenization theory and finite element analysis within a periodic base cell (PBC), elemental sensitivity numbers are established for gradually removing and adding elements in PBC. Numerical examples in 2D and 3D demonstrate the effectiveness of the proposed method for achieving convergent microstructures of cellular materials with maximum bulk or shear modulus. Some interesting topological patterns have been found for guiding the cellular material design.     

Stress‐Dependent Elastic Properties of Porous Microcracked Ceramics

Although ceramics are considered linear elastic materials, we have observed a non‐linear pseudo‐elastic behavior in porous cellular microcracked ceramics such as β‐eucryptite. This is attributed to the evolution of microstructure in these materials. This behavior is particularly different from that of non‐microcracked ceramics such as silicon carbide. It is shown that in microcracked materials two processes, namely stiffening and softening, always compete when a compressive external load is applied. The first regime is attributed to microcrack closure, and the second to microcracks opening, i.e. to a damage introduced by the applied stress. On the other hand rather a continuous damage is observed in the non‐microcracked case. A comparison has been done between the microscopic (as measured by neutron diffraction) and the macroscopic stress‐strain response. Also, it has been found that at constant load a significant strain relaxation occurs, which has two timescales, possibly driven by the two phenomena quoted above. Indeed, no such relaxation is observed for non‐microcracked SiC. Implications of these findings are discussed.     

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.     

Characterization of edge effects in cellular materials

Cellular solids constitute a unique class of materials possessing a high stiffness to weight ratio. Due to the high level of porosity in these materials (70 to 99.7%) one must utilize special testing considerations in order to obtain accurate results. One of these items has been referred to as edge effects and stems from the large scale macrostructure of cellular materials. This results in a dramatic decrease in the mechanical properties when testing small specimens having a large cell size. A reticulated vitreous carbon was used to characterize these effects for both elastic modulus and flexural strength measurements. It was observed that a critical specimen to cell size ratio is required to overcome these effects and achieve accurate results. A simple model is presented to help in predicting these edge effects.     

Arg-Gly-Asp (RGD) Modified Biomimetic Polymeric Materials

The new generation of biomaterials focuses on the design of biomimetic polymeric materials that are capable of eliciting specific cellular responses and directing new tissue formation. Since Arg-Gly-Asp (RGD) sequences have been found to promote cell adhesion in 1984, numerous polymers have been functionalized with RGD peptides for tissue engineering applications. This review gave the advance in RGD modified biomimetic polymeric materials, focusing on the mechanism of RGD, the surface and bulk modification of polymer with RGD peptides and the evaluation in vitro and in vivo of the modified biomimetic materials.     

柱胞夹芯复合材料设计加工及吸能性能研究现状

柱胞夹芯复合材料因其在吸能减振方面的优异性能以及比强度、比刚度高,被认为是新型吸能材料。为全面了解其在抗冲击吸能方面的优势,本文介绍了柱胞夹芯复合材料的基本概念;阐述了柱胞夹芯复合材料的吸能机理、吸能评估方法以及国内外设计的不同几何构型柱胞单元;分析了填充多孔材料对柱胞单元吸能性能的增强机理;概述了柱胞夹芯复合材料的不同加工工艺,比较各种加工工艺的优缺点及改进方法。文章最后对柱胞夹芯复合材料的发展前景进行了展望。     

Topological optimization for the design of microstructures of isotropic cellular materials

The aim of this study was to design isotropic periodic microstructures of cellular materials using the bidirectional evolutionary structural optimization (BESO) technique. The goal was to determine the optimal distribution of material phase within the periodic base cell. Maximizing bulk modulus or shear modulus was selected as the objective of the material design subject to an isotropy constraint and a volume constraint. The effective properties of the material were found using the homogenization method based on finite element analyses of the base cell. The proposed BESO procedure utilizes the gradient-based sensitivity method to impose the isotropy constraint and gradually evolve the microstructures of cellular materials to an optimum. Numerical examples show the computational efficiency of the approach. A series of new and interesting microstructures of isotropic cellular materials that maximize the bulk or shear modulus have been found and presented. The methodology can be extended to incorporate other material properties of interest such as designing isotropic cellular materials with negative Poisson's ratio.