Molecular-dynamics-based cohesive zone law for brittle interfacial fracture under mixed loading conditions: Effects of elastic constant mismatch

One approach for performing a finite-element simulation of interfacial fracture is to use a cohesive zone model. The cohesive zone model defines the interfacial traction–separation relation. Experimental determination of such a relation has been difficult. Most previous work has been confined to tensile loading, and much less has been devoted to mixed-mode loading conditions. Even so, specific laws are often assumed rather than predicted. Our recent work has used molecular dynamics (MD) simulation methods to derive a general cohesive zone law for the fracture between two brittle materials under any mixed-mode loading conditions. Here we extend our method and use it to explore the effect of elastic constant mismatch between adjacent materials. In particular, we construct two bilayer structures where the cohesive energies and lattice constants of the constituent materials are kept the same, but the elastic constant mismatch of the two materials in one structure differs from that in the other. We then use MD simulations to study the fracture and to derive the cohesive zone laws for both structures. The effect of elastic constant mismatch on fracture will then be discussed.     

The use of off-line part production to predict the tensile properties of parts produced by Selective Laser Sintering

Rapid Manufacturing, and specifically Selective Laser Sintering, has the potential to become one of the most useful manufacturing techniques of the future, largely as a result of the extremely high levels of geometric complexity which can be produced. As the use of these technologies becomes more widespread, so the amount, and variety, of materials available for use in these processes also increases. However, the Selective Laser Sintering process can be both expensive and time-consuming when testing new materials. A method of off-line casting has been proposed here, and the tensile properties of parts produced using this method are compared with the properties achieved in Selective Laser Sintered parts produced in the same materials. For the materials tested it has been shown that the casting method provided an acceptable correlation with the properties of the Selective Laser Sintered parts, rendering this a suitable method of assessing the properties of a Selective Laser Sintering material without the requirement to produce a full build.     

Water Thinnable Paint and the Plant Designer

More recent appraisal of water thinnable paints has necessitated consideration of new factors in assessing their value to industry. In Britain, the properties which have proved to be particularly attractive are the use of high-build (high solids, low viscosity) materials as well as increased corrosion resistance. To take full advantage of these new materials, the whole concept of plant design, materials and process schedules has been restudied. Results show that increased protection from corrosion, together with reductions in basic operating costs, such as fuel, labour and material, can be effected. The experience, largely gained in the automotive field, may be readily applied to other products.     

镀铬挂具绝缘材料的选用

镀铬挂具的非工作部位应用绝缘材料会明显降低铬酐和电流消耗,提高生产效率。在通用的镀铬工艺下,本文介绍了七种常见的绝缘材料的试验结果。试验发现：在镀槽镀铬液环境使用的绝缘材料,PP-R（聚丙烯）塑料或F4（白色）塑料的使用性能是比较优秀的;在其它非镀铬液环境使用的绝缘材料,可根据具体的使用条件选用。     

镁工业是能实现可持续发展的优势产业

镁合金是最轻的结构材料之一，发展镁合金对节能，环保具有重要意义，本文综述了我国发展镁工业的资源优势，镁合金的性能特点以及其在汽车，3C产品高档建筑装饰材料中的应用前景，镁合金作为战略性轻质材料和可收回绿色材料会倍受关注。     

Korrosionsbeständige metallische Werkstoffe für Rauchgas-Entschwefelungsanlagen

Corrosion resistant metallic materials for flue gas desulfurization plants Forced by environmental legislation installations for flue gas desulfurization (FGD) are presently being built to a large extent in the Federal Republic of Germany as in some other countries. Absorption by lime/limestone slurries is used in most cases for desulfurization. The components of the flue gas as well as the kind of process applied are of primary importance for the corrosive behaviour of the materials of construction. In view of pH values going down below 1 in some cases, chloride contents of occasionally more than 10% Cl^?, temperatures between 40 and 160°C and local deposits of solids it is the resistance to pitting and crevice corrosion which has to be considered in the first place while stress corrosion cracking and erosion corrosion are of minor importance. Therefore, only austenitic materials with molybdenum contents of more than 2 wt.-% have to be considered. According to the severity of the corrosive media these are predominantly alloys as e.g. Cronifer 1925 LCN (Alloy 904 LN), 1925 hMo (Alloy 904 LM) going up to the high alloyed nickel base materials Nicrofer 6020 hMo (Alloy 625) and 5716 hMo W (Alloy C-276), which exhibit molybdenum contents of 9 and 16 wt.-% and are to be used at places where corrosion is extremely severe as e.g. at the raw gas inlet. The use of such high alloyed materials plated on carbon steel has been tried successfully. Special attention has to be paid to all aspects of welding in order to avoid welds to become locations being vulnerable by corrosive attack. Therefore, welding of corrosion resistant materials in FGD units has been investigated extensively. The results of application oriented laboratory tests as well as practical experience with existing FGD units are to be considered. Correct use of corrosion resistant metallic materials will be an important contribution to minimizing repair and shut downs of FGD units and to extend their life.     

Laser based welding of cellular aluminium

Abstract

Lightweight materials are becoming increasingly important in construction because of the potential for savings in resources and energy. The use of cellular materials is a promising approach to reduce the weight of components further. In the last decade, significant progress has been made in the production of aluminium foams. However, the lack of techniques for the further processing of these new materials has so far prevented widespread industrial use. The present paper reports the results from laser welding of aluminium foam, and shows that the process is a productive joining method for this innovative material. Because of the spatially limited energy input of the laser, a collapse of the foam structure can be effectively avoided. Based on the investigations carried out on the welding of aluminium foams, the process has been transferred to the joining of cellular aluminium with solid materials. The characteristics of the seams were evaluated using micro-computer tomography and reflective light microscopy as well as static and dynamic strength tests.     

The effects of hydrogen on titanium aluminides

Advanced aerospace systems such as the national aerospace plane are slated to use hydrogen as a fuel. Thus, caution must be exercised in the use of materials which can exhibit degradation in mechanical properties on exposure to hydrogen. Although recent work shows that hydrogen has adverse effects on titanium aluminides, it can also be used to advan tage to improve processing and refine microstructure using the thermochemical processing technique.     

Structure and sorption characteristics of nanoporous carbon materials

Results of a study of the structure of porous carbon materials (PCMs) prepared by the carbonization of plant raw materials and the modification of oxidized or thermally expanded graphite have been described. It has been experimentally found that the studied materials have a porous fractal structure with an average micropore radius of 17–37 ?. Based on this finding and results of previous studies, it is reasonable to state that the studied materials can be effectively used as supercapacitor electrodes. Adsorption/desorption of vapors and an aqueous solution of ethyl alcohol has revealed that the resulting materials are not inferior to pharmaceutical activated carbon with respect to the studied parameter. At a temperature of 37°C, carbonized sunflower seed shells retain the adsorbate three times longer than activated carbon does; this feature makes it suitable for use in medical applications.     

Environmentally benign manufacturing: Current practice and future trends

The consideration of environmental issues in manufacturing has taken on increased importance in terms of global competitiveness. Life-cycle assessment tools enable analysis of the environmental efficiency of industrial processes. Often these focus on the product, with standardized or customized data provided on current processing practice. Environmental management of the total materials cycle must provide tools to evaluate the effect of changes in processing or material substitutions on a global basis, where materials use, reuse, component remanufacture, and materials recycling can be considered and the overall costs and impacts assessed. In this article, two examples of net-shape processing are discussed from this total materials cycle perspective.     

ADVANCED NICKEL-BASED AND NICKEL-IRON-BASED SUPERALLOYS FOR CIVIL ENGINEERING APPLICATIONS

The use of high-temperature materials is especially important in power station construction, heating systems engineering, furnace industry, chemical and petrochemical industry, waste incineration plants, coal gasification plants and for flying gas turbines in civil and military aircrafts and helicopters. Particularly in recent years, the development of new processes and the drive to improve the economics of existing processes have increased the requirements significantly so that it is necessary to change from well-proven materials to new alloys. Hitherto, heat resistant ferritic steels sufficed in conventional power station constructions for temperatures up to 550℃ newly developed ferritic/martensitic steels provide sufficient strength up to about 600 - 620℃. In new processes, e.g. fluidized-bed combustion of coal, process temperatures up to 900℃ occur. However, this is not the upper limit, since in combustion engines, e.g. gas turbines. Material temperatures up to 1100℃ are reached locally. Similar development trends can also be identified in the petrochemical industry and in the heat treatment and furnace engineering. The advance to ever higher material temperatures now not only has the consequence of having to use materials with enhanced high-strength properties, considerable attention now also has to be given to their chemical stability in corrosive media. Therefore not only examples of the use of high-temperature alloys for practical applications will be given but also be contributed to some general rules for material selection with regard to their high-temperature strength and corrosion resistance.     

Spark plasma sintering for multi-scale surface engineering of materials

Recently, significant progress has been made in understanding the effect of multi-scale microstructural features, including nano-, micro-, and macro-features, on the properties of materials. Controlling the length scale of micro-structural features provides tremendous opportunities for enhancing the properties of materials, including extraordinary strength and hardness, unprecedented damage from tribological contacts, and improvements in a number of functional properties of the materials. Spark plasma sintering (SPS) process which combines the effects of uniaxial pressure and pulsed direct current is becoming increasingly important for the processing of bulk shapes of amorphous and nanostructured materials. These materials can also be good candidates for high-performance coatings. This article presents a review of our ongoing efforts to use SPS to produce engineered coatings of amorphous and nanostructured materials for various applications, including structural, tribological, and biomedical applications.     

Nitrogen-atomized,nickel-based,corrosion-resistant alloys

Nitrogen gas atomization has been used for many years to produce iron-based powder-metal materials such as stainless and tool steels. However, it is more typical to use argon atomization with nickel-based alloys because it avoids the formation of nitrides that, in some cases, can be detrimental to the mechanical properties of these materials. In this article, two nickel-based materials— alloy 625 and alloy 690—normally used for applications where corrosion resistance is of primary importance were evaluated in their nitrogen-atomized powder metal form. Nitrogen atomization uncovered attributes of these nickel alloys that are not present in their conventionally produced counterparts or in argon-atomized versions of the same compositions.     

Some observations on the compatibility ofstructural materials with molten lead

Exploratory experiments have been carried out relating to the use of molten lead as a coolant in advanced nuclear reactors. It has been found that the attack of molten lead on structural materials is qualitively related to the solubility of the solid in the lead. The attack can be greatly reduced by the presence of a protective oxide film on the solid and the ease of formation of such a film depends on the nature of the solid and the oxidizing potential of the lead. The effectiveness as an ‘inhibitor’ of titanium dissolved in the lead has been confirmed. Mass transfer has been shown to be very inefficient, at least under the experimental conditions used, and reasons for this are discussed. A number of ceramic materials have been shown to be very resistant. A cast iron exhibited ‘growth’. With two exceptions a range of coated materials showed unsatisfactory behaviour. An exploratory experiment on the susceptibility of molybdenum to liquid metal embrittlement did not result in failure of the specimen.     

Integrated computational materials engineering: A new paradigm for the global materials profession

Conclusion Integrated computational materials engineering is a field of study whose time has come. It promises to link manufacturing and design via advanced materials models in a seamless, integrated computational environment. The feasibility of ICME and its benefits have been demonstrated by several projects that have developed methods which are in use in the aerospace and automotive industries. To fully realize the potential of ICME, anumber of technical, cultural, and organizational challenges have been identified and must be overcome.     

几种表面分析技术在材料研究中的应用

从材料及所处的体系综合考虑,材料的物理化学性能不仅取决于材料的本征特性和环境条件,很重要的一个方面就是材料与环境的交接面的特性。因此,材料的表面(界面)研究一直是材料研究的重点。本文简要地讨论了几种表面(界面)分析技术的特点及其在材料研究中的应用情况。作者认为,只有充分了解各种表面分析技术的特点．综合运用多种表面分析技术,才能实现对材料表面更深入、更全面的认识。     

金属系牙科材料的应用现状及部分元素的毒副作用

本文对金属纱牙科材料的组成、性能，适用场合，存在问题及发展趋势进行了综合评述。认为汞、镍，铜，铝，铍，铬，钴，钒，钯元素均具有细胞毒性作用，在牙科材料及其它生物医学材料中应尽量避免使用；而元素钛、铌，锆，锡，钼，钽和铁是无毒性元素，可以作为改善生物医学材料力学性能，耐蚀性能及生物相容性的候选元素，为新型牙科合金材料及其它生物医学材料的开发研究提供选材依据。钛合金作为牙科材料是未来牙科材料的发展趋势     

Frequency response of different couplant materials for mounting transducers

Sensors often are piezoelectric crystal transducers that convert movement (a variation of pressure) into an electrical voltage. Several non-destructive techniques involve the use of transducers, such as sonic testing, tomography, acoustic emission and pulse-impact echo. There are different types of transducers according to their different aims and applications, but in all cases the mounting of a sensor is an essential requirement in order to record good quality data—a good acoustic coupling between the transducer and the surface of the structure has to be ensured. It is common practice to use Cyanoacrylate adhesive glue (e.g. superglue) for most applications, but the authors found its use problematic during temporary installations due to the difficulties encountered to remove the sensor at the end of the experiment. For this reason, a study has been carried out to investigate possible alternative couplant materials. Eight different materials have been selected, and their amplitude of response in terms of time-domain and the frequency-domain has been compared. A final evaluation based on several pre-defined criteria has then been obtained, showing the feasibility of ‘plasticine’ as a valid alternative to superglue.     

Characterization of deformation induced surface hardening during cryogenic turning of AISI 347

The use of cryogenic cooling in material removal processes has been reported by several researchers. The objectives were enhanced tool life and an expanded range of machinable materials. In this paper, a novel application of cryogenic cooling is presented: its use achieve direct surface hardening of metastable austenitic steels during cutting. Metastable austenite can transform into martensite due to plastic deformation if a sufficiently low temperature is maintained. In order to use this effect during cutting, cryogenic conditions must be maintained at all times. With this approach, cutting and hardening can be combined in one process.     

Degradation of Lignocellulosic Materials and Its Prevention

Lignocellulose-based materials, such as wood, have long been used for structural applications, but their inherent susceptibility to biological and physical degradation sometimes limits their use and leads to early replacement. Concerns about the contributions about the environmental impacts of all materials have sparked renewed interest in using renewable materials in structural applications. An important aspect of any increased use of these materials will be enhancing their durability. This review examines the inherent susceptibility of lignocellulose-based materials to degradation, using wood as the primary example, and then it outlines the research underway to improve these properties.