WADSWORTH Jeffrey and FLUSS Michael(Chemistry and Materials Science Directorate
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Lawrence Livermore National Laboratory
,
Livermore
,
CA 94551)
金属学报(英文版)
The role of the National Laboratories is summarized from the era of post World War II to the present time. The U.S. federal government policy for the National Laboratories and its influence on their materials science infrastructure is reviewed with respect to .determining overall research strategies, various initiatives to interact with industry (especially in recent years),building facilities that serve the nation, and developing leading edge research in the materials sciences. Despite reductions in support for research in the U.S. in recent years, and uncertainties regarding the specific policies for Research &Development (R&D) in the U.S., there are strong roles for materials research at the National Laboratories. These roles will be centered on the abilities of the National Laboratories to field multidisciplinary teams, the use of unique cutting edge facilities, a focus on areas of strength within each of the labs,increased teaming and partnerships, and the selection of motivated research areas. It is hoped that such teaming opportunities will include new alliances with China, in a manner similar, perhaps, to those recently achieved between the U.S. and other countries.
关键词:
: U.S. Materials Science. U.S. National Laboratories and Facilities
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null
TG.Nieh(Lawrence Livermore National Laboratory
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P.O.Box 808
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L-350
,
Livermore
,
CA 94551
,
USA )
材料科学技术（英文）
Intermetallic beryllides are potential light-weight, high-temperature structural materials. In this paper. the processing techniques, microstructure. deformation, and oxidation properties of intermetallic beryllides are described. In addition to nickel beryllides (NiBe). which is treated as a model system.other high beryllium-containing refractory beryllides, such as Nb2 Be17. VBe12. are also studied.The room temperature deformation and high-temperature creep properties of these beryllides are repor4ed. At room temperature. NiBe exhibits certain tensile ductility (~ 1 .3%). but all other beryllides are essentially brittle. Nonetheless, these beryllides become ductile at temperatures above approximately 1000℃. Their creep properties are presented. The creep properties are compared with those of intermetallic aluminides. Also. a comparison is made between the ductile-to-brittle transition behaviour of intermetallic beryllides and that of aluminides. Although beryllides are generally oxidation resistant at high temperatures, some beryllides, e.g., ZrBe13, suffer the pest reaction during oxidation at intermediate tem peratures. The pest mechanisms are proposed
关键词:
NIEH Tai-Gang
,
WADSWORTH Jeffrey (Lawrence Livermore National Laboratory
,
Livermore
,
CA 94550
,
USA)
金属学报(英文版)
Superplasticity in intermetallic alloys is reviewed. Intermetallics which have been demonstrated to be superplastic include nickel-based (Ni_3Al, Ni_3Si), titanium-base (Ti_3Al, TiAl), and iron-base (Fe_3Al, FeAl) alloys. These alloys are primarily finegrained, two phase materials. But, superplasticity was also observed in some iron-base alloys which were in coarsegrained conditions. These alloys behave like Class I solid solution. The superplastic deformation mechanisms as well as microstructural characteristics are discussed. The superplastic forming of intermetallics is also briefly addressed.
关键词:
: Superplasticity
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null
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null
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null
材料工程
开孔泡沫塑料因为其独特力学属性特别是轻质量、高吸能性而在工业界得到广泛应用,如座椅、头盔、空间飞行器等.但这种塑料的材料属性却是不同形式的微观结构和基体材料属性综合作用的结果.广泛的研究都已开展起来,包括分析法、试验法和计算模拟,这些研究增加了我们对开口泡沫材料物理行为的理解.计算模拟已逐渐被证实是一种非常有效、有价值的工具,它可以在微观水平调查研究材料行为并评估其在宏观水平的影响.计算模拟比试验测试能更深入理解变形机理,比分析法得到更真实的模型结果.但是,直到现在,开口泡沫塑料微观结构的复杂拓扑使划分网格的困难显而易见,这种困难为分析力学特性所采用的最流行的基于物理学的有限元方法之有效应用提供了障碍.在本文中,一种新的基于图像的网格划分方法被第一次使用来分析复杂结构塑料的力学特性,这种分析是基于高精度的计算机断层扫描数据(微观CT或X波段微波发射机).数据图像被导人到商用三维建模软件ScanIP/+ScanFE(Simpleware Ltd.)生成几何形状和拓扑结构都很精确的三维有限元模型.这种技术将CT扫描数据直接自动转化成任意复杂域的六面体或六面体、四面体混合网格模型.网格模型的精度仅依赖于CT成像系统的精度.复杂单相或多相材料可被直接划分网格,从而解决了诸如多孔材料中流体引起的变形等流固耦合问题.对于本文中选用的开孔泡沫塑料,建立了包含1392751个线性四面体单元和360703个节点的有限元模型,并用LSDYNA显式模块(Livermore Software Teclnnology Corp.)进行了准静态和动态应力一应变分析,考虑了不同加载速率和线弹性及弹塑性材料属性的影响.加载方式为两块刚性板从两侧压缩模型,并设定了刚性板和塑料模型之间的滑动接触关系.所有的求解都是在LS-DYNA中进行的.本项研究的目的是介绍材料研究中的一种建模新方法,这种方法可以解决几何拓扑复杂的问题,精度很好,比其他方法节约了大量时间.此种复杂微细观结构的快速强健建模方法为材料科学家提供了强大的新工具,使他们能探索不同参数对新材料性能的影响,成为材料研究中的分析法和试验法的有益补充.上述的建模方法一定会逐渐成为复合材料研究中逆向建模方法的关键技术.
关键词:
