关键词： 表面涂层   摩擦学   多层纳米   金属薄膜   微结构  

关键词： 计算微观力学   疲劳裂纹   材料微结构   并行算法   多域边界元   数值方法   微结构损伤  

摘要： 该文以显微动态疲劳拉伸实验为依据,根据计算微观力学理论的思想体系,研究铝锂二元合金模型材料的强韧化及损伤断裂机制,进一步充实、完善计算微观力学的数值分析方法,使其解题能力大大提高.该文主要完成以下工作:①进行显微动态疲劳拉伸实验,仔细观察了微裂纹的萌生、演化及其径迹,记录了微裂纹长度及相应的循环次数,得到了da/dN在微裂纹扩展阶段的新规律,用计算机存储了大量微裂纹演化照片,并在实验过程中对不同程度的损伤试样作了透射电镜分析和彩色金相照片,为进一步计算微观力学的研究打下了基础;②建立了\'随机投放,逐点扫描\'的自动划分计算微观力学计算网格模型的方法;③改进和完善了计算微观力学模型和理论;④首次把并行算法引入计算微观力学理论;⑤模拟计算了扩展性微裂纹萌生的寿命.在这里通过微观计算,在具体微观实验的基础上,对二元铝锂合金模型材料的微裂纹萌生寿命进行了计算.有了更多的微观实验,这种计算方法适合于全寿命计算.

关键词： 颗粒弥散   纳米晶   铝合金   微观结构   力学性能  

摘要： 本文对新型颗粒弥散铝基纳米晶薄带的微观结构、相转变和力学性能作了详细研究.结果表明，随着混合稀土（Mm）含量的增加，快凝al-Fe－V－Si合金α-al晶粒和弥散颗粒不断细化，形成颗粒弥散铝基纳米晶材料.稀土元素在快凝过程中促使亚稳相al8Fe4Mm的形成，抑制α－al13（Fe，V）3Si相的析出.含0.5％和1.0％Mm（原子分数）纳米合金在673K附近al8Fe4Mm转变为α－al13（Fe,V）3Si相.含1％Mm快凝合金形成很细的颗粒弥散纳米晶材料,其断裂强度和疲劳强度比微晶al-Fe－V－Si合金高出1倍，且具有更好的热稳定性.

关键词： 半导体   碳化硅   硅基纳米   微结构  

摘要： 在室温下将C+注入硅衬底，注入能量和剂量分别为50keV，2×1016cm－2．经高温退火形成，β-SiC颗粒沉淀．用傅里叶变换红外吸收谱，光电子能谱以及高分辨率透射电镜对注入样品中的纳米β-SiC及其微结构作了分析．

关键词： energy absorption   polymer composite materials   crushing   crashworthiness  

摘要： Traditionally, metals are used for crashworthy structural applications, mainly due to their plastic deformation characteristics that enable them to absorb impact energy in a controlled manner. Unlike the metals, polymer composite materials display little plastic deformation characteristics. The use of polymer composites for crashworthy structural applications is a major challenge for the composite community. Current research work dearly suggests that when properly designed, polymer composite materials absorb more energy per unit mass of material than the conventional metals. This article describes the effect of microstructure variables, such as type of reinforcements and matrices, reinforcement architecture and reinforcement/matrix interface bond strength, on the energy absorption characteristics of polymer composite materials. (C) 1998 Elsevier Science Ltd. All rights reserved.

关键词： textile composites   microstructure   mechanical properties   design  

摘要： Textile composites are emerging as viable alternatives to other forms of composites in various structural applications. Understanding the dependence of overall mechanical properties of textile composites on its microstructure is important to derive an effective design. The present study is on the effect of geometrical and material properties of woven fabric (WF) composite microstructure on its overall mechanical properties. It is seen that the microstructural properties of WF composites give large flexibility to a designer to derive the required structural properties by judicially varying both the geometry and material parameters. (C) 1998 Elsevier Science Ltd. Ail rights reserved.

摘要： In the field of materials science there is an enormous range of landscapes (microstructures) from the atomic level to the macro level. The structures sometimes are periodic -dislocations in boundaries, spinodals, dendrites, fluxons, polysynthetic twins, etc., but more often they are aperiodic or quasiperiodic and therefore difficult to describe quantitatively. The structures in real materials are also usually metastable. What is certainty true is that the properties of materials are controlled by the microstructure at all levels. A summary of this relationship is given.

摘要： In materials that exhibit strain softening due to dislocation multiplication and/or glide-induced destruction of dislocation obstacles, pronounced slip localization may be observed. Plastic deformation after yield is characterized by a coarse and inhomogeneous slip pattern. In the present work a statistical model of the microstructural evolution during strain softening is formulated. Both multiplication softening and structural softening due to obstacle destruction are taken into account. The interplay between strain softening, slip localization and the formation of an inhomogeneous microstructure is studied. It is demonstrated that multiplication softening leads to transient slip heterogeneities only, while structural softening gives rise to a more permanent localization of slip which manifests itself through the formation of obstacle-free slip channels within a microstructure of initially high obstacle density.

关键词： mushy zone   coarsening   Ostwald ripening  

摘要： This paper employs a recent macroscopic theory of the authors [Int. J. Non-Lineal Mech. 25, 319 (1990)] to discuss the phase coarsening, or Ostwald ripening, of a homogeneous mushy zone of a pure material (a) under adiabatic conditions and (b) when the system is isothermally held. The influence of the solid phase volume fraction on the coarsening kinetics is investigated. For the adiabatic evolution, comparison is made with the high precision thermal decay experiments of Glicksman et al. [Metall. Trans. A 23, 659 (1992)]. (C) 1997 Elsevier Science Ltd.

关键词： 离子束溅射   微观结构   光学性质   半导体薄膜技术  

摘要： 采用透射电子显微镜（ＴＥＭ）对ＧｅＳｉＯ２纳米颗粒镶嵌薄膜样品的形貌和结构进行了观察研究。测量了不同直径纳米锗颗粒镶嵌薄膜的吸收光谱，并在不同激发光能量下对样品进行了室温荧光光谱研究，发现在中心波长为４２０ｎｍ处有一个较强的光致荧光峰。研究结果表明纳米锗粒子的相结构和电子能级结构同常规的大块锗晶体相比均发生显著的改变。