Nano finish grinding of brittle materials using electrolytic in-process dressing (ELID) technique

Recent developments in grinding have opened up new avenues for finishing of hard and brittle materials with nano-surface finish, high tolerance and accuracy. Grinding with superabrasive wheels is an excellent way to produce ultraprecision surface finish. However, superabrasive diamond grits need higher bonding strength while grinding, which metal-bonded grinding wheels can offer. Truing and dressing of the wheels are major problems and they tend to glaze because of wheel loading. When grinding with superabrasive wheels, wheel loading can be avoided by dressing periodically to obtain continuous grinding. Electrolytic inprocess dressing (ELID) is the most suitable process for dressing metal-bonded grinding wheels during the grinding process. Nano-surface finish can be achieved only when chip removal is done at the atomic level. Recent developments of ductile mode machining of hard and brittle materials show that plastically deformed chip removal minimizes the subsurface damage of the workpiece. When chip deformation takes place in the ductile regime, a defect-free nano-surface is possible and it completely eliminates the polishing process. ELID is one of the processes used for atomic level metal removal and nano-surface finish. However, no proper and detailed studies have been carried out to clarify the fundamental characteristics for making this process a robust one. Consequently, an attempt has been made in this study to understand the fundamental characteristics of ELID grinding and their influence on surface finish.     

纳米/超细Ti(CN)基金属陶瓷的研究进展

概述了纳米/超细Ti(CN)基金属陶瓷的研究进展,重点对纳米Ti(CN)粉末的制备方法、纳米/超细Ti(CN)基金属陶瓷烧结过程中相组织的变化以及烧结工艺进行了介绍.指出成功制备纳米/超细Ti(CN)基金属陶瓷的关键在于控制烧结过程中Ti(CN)晶粒及环形相的长大,探索新的快速烧结方法.     

纳米ZnO在NR/SBR材料中的应用研究

研究了不同类型的ZnO在NR/SBR材料中的应用,并对其拉伸性能、硬度、耐磨性、热性能进行表征.结果表明:与添加5份普通ZnO的NR/SBR材料相比,添加3份的纳米ZnO的NR/SBR材料的拉伸强度、硬度、耐磨性和耐热性均提高,且纳米ZnO用量减半时其硫化特性与普通ZnO相当.     

Grain growth in porous two-dimensional nanocrystalline materials

Grain growth in two-dimensional polycrystals with mobile pores at the grain boundary triple junctions is considered. The kinetics of grain and pore growth are determined under the assumption that pore sintering and pore mobility are controlled by grain boundary and surface diffusion, respectively. It is shown that a polycrystal can achieve full density in the course of grain growth only when the initial pore size is below a certain critical value which depends on kinetic parameters, interfacial energies, and initial grain size. Larger pores grow without limits with the growing grains, and the corresponding grain growth exponent depends on kinetic parameters and lies between 2 and 4. It is shown that for a polycrystal with subcritical pores the average grain size increases linearly with time during the initial stages of growth, in agreement with recent experimental data on grain growth in thin Cu films and in bulk nanocrystalline Fe.     

Nucleation of cracks in two-dimensional periodic cellular materials

This paper describes the nucleation and propagation of cracks in brittle cellular material. Four basic patterns with triangular, square, hexagonal and kagome-type cells are considered. The cracks propagate by sequential failure of critical elements. The analysis technique hinges on the combined use of the structural variation method and the representative cell method. While the latter allows for the analysis of periodic structures under arbitrary loads, by means of the discrete Fourier transform, the former analyzes modified structures (the cracked lattices) on the basis of analysis of the pristine structure (the periodic lattices). Within the assumptions of Bernoulli–Euler beam theory the suggested method for the analysis of infinite cracked lattices is exact. Although most cracks follow intuitive paths it was found that the microstructure of cellular materials has a significant influence on the crack pattern.     

Contents of volume 45 (1990)

Contents of volume 45 (1990)     

二维MXene材料在气体传感器领域的应用进展

MXene材料是由前过渡金属碳、氮化物组成的无机化合物,二维MXene及其复合材料具有类石墨烯层状结构、高比表面积、优异的导电性和丰富的表面活性位点,近年来在材料领域成为研究热点.本文聚焦二维MXene材料在气体传感器领域的应用前景,从MXene和气敏性能等角度进行了综述,重点对MXene及其(无机/有机)复合材料用作...     

Leadership in Innovators and Defenders: The Role of Cognitive Personality Styles

This research is based on a mixed strategic typology, combining innovators of Miller and Roth (1994, “A Taxonomy of Manufacturing Strategies,” Management Science, 40 (3), 285–304) and defenders of Miles et al. (1978, “Organizational Strategy, Structure and Process,” Academy of Management Review, 3, 546–562) and supported by the perception–evaluation personality model of Jung (1923, Psychological Types, London, Routledge & Kegan). Leadership model having five underlying constructs—group cohesion, intellectual flexibility, leader cognitive styles, leadership styles and leadership roles—is identified and studied. At first, respondent firms from various sectors are classified as innovators and defenders. Second, the constructs are empirically tested on them. Important findings suggest that innovators have intuitive-feeling leaders and defenders have sensing-thinking leaders, two of the four personality types proposed by Jung (1923). It has also been found that innovators are higher in the degree of intellectual adjustment; in the idea generation and nurturant phase leaders exhibit intuitive-feeling personality style; concept creators also exhibit the same. These findings may be used in organizations for leadership building, finding out best candidate job-fit and organization-fit during recruitment, and also for training and development of the leaders.     

Recent advances in anisotropic two-dimensional materials and device applications

Two-dimensional(2D)materials,such as transition metal dichalcogenides(TMDs),black phosphorus(BP),MXene and borophene,have aroused extensive attention since the discovery of graphene in 2004.They have wide range of applications in many research fields,such as optoelectronic devices,energy storage,catalysis,owing to their striking physical and chemical properties.Among them,anisotropic 2D material is one kind of 2D materials that possess different properties along different directions caused by the intrinsic anisotropic atoms5 arrangement of the 2D materials,mainly including BP,borophene,low-symmetry TMDs(ReSe2 and ReSa)and group IV monochalcogenides(SnS,SnSe,GeS,and GeSe).Recently,a series of new devices has been fabricated based on these anisotropic 2D materials.In this review,we start from a brief introduction of the classifications,crystal structures,preparation techniques,stability,as well as the strategy to discriminate the anisotropic characteristics of 2D materials.Then,the recent advanced applications including electronic devices,optoelectronic devices,thermoelectric devices and nanomechanical devices based on the anisotropic 2D materials both in experiment and theory have been summarized.Finally,the current challenges and prospects in device designs,integration,mechanical analysis,and micro-/nano-fabrication techniques related to anisotropic 2D materials have been discussed.This review is aimed to give a generalized knowledge of anisotropic 2D materials and their current devices applications,and thus inspiring the exploration and development of other kinds of new anisotropic 2D materials and various novel device applications.     

Piezoelectric properties in two-dimensional materials: Simulations and experiments

The piezoelectric effect, discovered in 1880 by Jacques and Pierre Curie, effectively allows to transduce signals from the mechanical domain to the electrical domain and vice versa. For this reason, piezoelectric devices are already ubiquitous, including, for instance, quartz oscillators, mechanical actuators with sub-atomic resolution and microbalances. However, the ability to synthesize two-dimensional (2D) materials may enable the fabrication of innovative devices with unprecedented performance. For instance, many materials which are not piezoelectric in their bulk form become piezoelectric when reduced to a single atomic layer; moreover, since all the atoms belong to the surface, piezoelectricity can be effectively engineered by proper surface modifications. As additional advantages, 2D materials are strong, flexible, easy to be co-integrated with conventional integrated circuits or micro-electromechanical systems and, in comparison with bulk or quasi-1D materials, easier to be simulated at the atomistic level. Here, we review the state of the art on 2D piezoelectricity, with reference to both computational predictions and experimental characterization. Because of their unique advantages, we believe 2D piezoelectric materials will substantially expand the applications of piezoelectricity.     

Nano/micro lithium transitionmetal (Fe, Mn, Co and Ni) silicate cathode materials for lithium ion batteries

Lithium transitionmetal (Fe, Mn, Co, Ni) silicate cathode materials are new promising substituting cathode materials for lithium ion batteries. They had caught the researchers' eyes in the past several years. Nowadays, there are growing interests for silicate cathode materials in the field of lithium ion batteries. Among the silicate cathode materials, Li2FeSiO4 is the most promising cathode materials because of its high structure stability, high reversible capacity, high electronic conductivity and the abundant resource of iron and silicon. Although Li2MnSiO4 and Li2CoSiO4 have much higher theoretic specific capacity than Li2FeSiO4, they all have inferior electrochemical behaviours due to different reasons. There are only calculation results about Li2NiSiO4 till now. This brief critical review firstly discussed some papers about the first-principle calculation of Li2MSiO4 (M=Fe, Mn, Co Ni), and then collects and discusses relevant papers and recent patents about the fabrication, structure, particle size and electrochemical performance of nano/micro Li2MSiO4 (M=Fe, Mn, Co Ni) and their composites. Finally, the future challenges of Li2FeSiO4 are also discussed.     

纳米二氧化钛光催化剂研究进展

半导体光催化技术对多种有机物有明显的降解效果,具有广阔的应用前景,近年来,半导体光催化已成为光化学领域及环境保护领域中的研究热点之一.介绍了近年来国内外二氧化钛(TiO2)半导体光催化技术的研究进展,主要涉及TiO2光催化机理、高活性TiO2光催化荆的制备与改性、TiO2在环境保护中的应用等方面的研究,并指出以后的研究方向.     

The boundary contour method for two-dimensional Stokes flow and incompressible elastic materials

 A variant of the boundary element method, called the boundary contour method (BCM), offers a further reduction in dimensionality. Consequently, boundary contour analysis of two-dimensional (2-D) problems does not require any numerical integration at all. While the method has enjoyed many successful applications in linear elasticity, the above advantage has not been exploited for Stokes flow problems and incompressible media. In order to extend the BCM to these materials, this paper presents a development of the method based on the equations of Stokes flow and its 2-D kernel tensors. Potential functions are derived for quadratic boundary elements. Numerical solutions for some well-known examples are compared with the analytical ones to validate the development. Received 28 August 2001 / Accepted 15 January 2002     

In situ microscopy techniques for characterizing the mechanical properties and deformation behavior of two-dimensional (2D) materials

Due to the atomic thickness and planar characteristics, two-dimensional (2D) materials such as graphene and transition metal dichalcogenides (TMDs) are considered to be excellent electronic materials, which endow them with great potential for future device applications. The robust and reliable application of their functional devices requires an in-depth understanding of their mechanical properties and deformation behavior, which is also of fundamental importance in nanomechanics. Considering their exceedingly small sizes and thicknesses, this is a very challenge task. In situ microscopy techniques show great superiority in this respect. This review focuses on the progress in in situ microscopy techniques (including atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM)) in characterizing the mechanical properties and deformation behavior of 2D materials. The technical characteristics, advantages, disadvantages, and main research fields of various in situ AFM, SEM, and TEM techniques are analyzed in detail, and the corresponding mechanical scenarios from point to plane are realized, including local indentation, planar stretching, friction sliding between atomic layers and atomic movement mechanisms. By virtue of their complementary advantages, in situ integrated microscopy techniques enable the simultaneous study of various mechanical properties, nanomechanical behavior, and inherent atomic mechanisms of 2D materials. Based on the present research, we look forward to further optimized in situ integrated microscopy techniques with high spatiotemporal atomic resolution that can reveal the dynamic structure-performance correlations and corresponding atomic mechanisms between the physical properties, such as mechanical, electrical, optical, thermal, and magnetic properties of 2D materials and their crystal structures, electronic structures, atomic layers, defect densities and other influencing factors under multifield coupling conditions. This will provide beneficial predictions and guidance for the design, construction and application of 2D material-based mechanoelectronic, piezoelectric, photoelectric, thermoelectric, etc. nanoelectronic devices.