复合材料空心飞轮多环套装整体变形及应力简化精细分析

采用多环过盈装配是解决复合材料飞轮径向强度过低的有效途径之一。本文作者采用平面应力简化模型,提出了计及过盈配合后变形导致实际过盈量增大计算飞轮套装后的初终应力分布的方法;提出了基于叠加原理计算多环过盈装配旋转飞轮应力的方法;提出了保证飞轮旋转时配合界面不脱离的相关临界转速的概念和计算方法。算例分析表明:过盈配合后的变形对初终应力的影响不能忽略;过盈量和套装环数与飞轮的初终应力和相关临界转速有密切的关系。     

GH2027铁基高温合金的第二相研究

运用电子显微分析和波谱分析等方法对ＧＨ２０２７合金的第二相进行了研究，结果表明，合金晶界相主要是片状Ｍ６Ｃ和薄膜状Ｍ２３Ｃ６，经波纹图样测得其错配度约为３％，晶内Ｍ６Ｃ和Ｍ２３     

Models and observations of fcc/bcc interfaces

Whereas models of the structure and periodicity of CSL or near CSL high angle grain boundaries are relatively well developed and have been to some extent verified by experiment, the nature of more general (e.g. fcc/bcc) interfaces is very imperfectly understood. One of the major differences between homo- and heterophase boundaries is the occurrence, in the latter case, of reproducible orientation relationships due to the crystallographic requirements of phase transformation (e.g. a glissile interface for martensitic growth, low energy interfaces for classical nucleation). A review is given of the relationships commonly observed to obtain between fcc and bcc crystals (as well as ordered phases based upon these structures). Within a given relationship, it is possible to use models of the available interfaces to predict their dislocation content; the success of the various approaches is considered. It is shown that the dislocation arrays identified on fcc/bcc boundaries are consistent with the occurrence of a primary structural relaxation, but that the latter does not appear to be complete. Possible reasons for this are discussed, together with the extent to which secondary structural models may be applicable. Attempts to rationalize the observed orientation relationships and morphologies are discussed, and it is pointed out that these all rely on searches for situations of minimum primary misfit, but that the way in which the latter is quantified determines the results of the analyses. Nevertheless, the implication is that the primary misfit does appear to determine the actual behaviour, though no structural or mechanistic conclusions can safely be drawn from this observation.     

考虑热不协调性的镍基单晶合金细观力学分析SCIEI

基于镍基单晶合金的细观结构特征，本文建立两个微胞模型对热不协调性作了系统的模型计算和分析．微胞模型１是以一个γ和γ’为考察对象，微胞模型２是以多个γ和γ’为考察对象，详细的分析表明，这两个模型有一定的等效性，但模型２可分析边界条件更宽的情况．基于微胞模型，对两相合金的临界分切应力进行了分析，结果表明，宏观临界分切应力可用考虑热不协调性的有限元法来处理，所得结果还可推广到较大的γ’相体积分数ｆ的情况．考察了热不协调性对回火状态时γ’形状变化的影响，初步的定量分析表明，热内应力是γ’粗化的一个主要驱动力．     

Recent progress in the modeling of high-temperature creep and its application to alloy development

Recent progress in the understanding of high-temperature creep of alloys is discussed in the context of theoretical modeling and its application to alloy development. Emphasis is placed upon those engineering alloys specifically designed for high-temperature applications, such as precipitation and dispersion-strengthened (DS) alloys and metal-matrix composites (MMCs). Currently, these theoretical models use one of two different approaches, (a) a phenomenological approach, which is used in such models as those based on the internal stress concept, and those based on empirical creep equations; and (b) micromechanical models that are based on dislocation mechanisms and the interactions of dislocations with solute atoms, second-phase particles, and other reinforcements such as fibers. All these theoretical models have a common goal, namely, the understanding of high-temperature strengthening mechanisms and the relationship between high-temperature strength and the micromechanical mechanisms during high-temperature plastic deformation of the alloys. These theoretical studies can provide information that is useful in alloy design and processing, such as the selection of alloy chemistry, and the optimization of phase microstructural features (e.g., reinforcement amount, shape, size, and distribution; matrix grain size; and matrix and reinforcement interfaces) by optimization of processing methods. L. Shi, Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22901, USA     

A kinetics formulation for low-temperature plasticity

The mechanism of low-temperature plastic deformation is controlled by thermally activated dislocation movements. An evolutionary constitutive law based on the principles of deformation kinetics is described in this article. The constitutive law is expressed with a sinh function designed for computational efficiency. It is derived from rigorously defined kinetics principles. The approximation involved in the sinh function is defined so that in applications an exact evaluation can be made of the validity limits. The system of the constitutive law and the external constraints lead to the operational equations. Applications are developed for constant strain-rate loading, constant stress-rate loading, stress relaxation, creep, and ratchetting processes. The analysis provides a unified treatment for low-temperature plastic deformation.     

Cu/MgO界面位错的高分辨电子显微镜研究

用高分辨透射电子显微镜对内氧化产生的Cu/MgO界面进行了研究，观察到了取向关系相同的两种不同界面。并运用近重位点阵模型对其界面结构进行了研究，求出了失配位错的3个Burgers矢量和次级位错的3个Burgers矢量，它们分别为：b1^→=1/4[011]MgO,b2^→=1/2[100]Cu,b3^→=1/4[01^-1]MgO;b1^→′=1/12[101]Cu(或1／99[755]MgO),b2^→′=1/12[101^-]Cu（或1/99[75^-5^-]MgO),b3^→′=1/6[010]Cu(或1／10[01^-1]MgO)失配位错之间的距离与实验测量结果符合得很好。     

Elemental partitioning,lattice misfit and creep behaviour of Cr containing γ′ strengthened Co base superalloys

Novel Cr containing Co-Al-W base superalloys were studied by atom probe tomography and neutron diffraction. Cr is found to predominantly partition to the γ matrix and decrease partitioning of W to γ′. Furthermore, Cr significantly enhances the γ′ volume fraction, decreases the γ/γ′ lattice misfit and deteriorates the creep resistance. Addition of Ni to the Cr containing alloys affects partitioning of W and Al, further decreases the lattice misfit and results in the formation of irregularly shaped precipitates. Al, W and Cr tend to occupy the ‘B'sublattice in the γ′-A₃B phase (L1₂ type), while Co and Ni reside in the ‘A' sublattice.     

一种基于语料特性的聚类算法

为寻求模型不匹配问题的一种恰当的解决途径,提出了基于语料分布特性的CADIC(clustering algorithm based on the distributions of intrinsic clusters)聚类算法。CADIC以重标度的形式隐式地将语料特性融入算法框架,从而使算法模型具备更灵活的适应能力。在聚类过程中,CADIC选择一组具有良好区分度的方向构建CADIC坐标系,在该坐标系下统计固有簇的分布特性,以构造各个坐标轴的重标度函数,并以重标度的形式对语料分布进行隐式的归一化,从而提高聚     

A study of the influence of grain boundaries on short crack growth during varying load using a dislocation technique

The propagation of short cracks in the neighbourhood of grain boundaries have been investigated using a technique were the crack is modelled by distributed dislocation dipoles and the plastic deformation is represented by discrete dislocations. Discrete dislocations are emitted from the crack tip as the crack grows. Dislocations can also nucleate at the grain boundaries. The influence on crack growth characteristics of the distance between the initial crack tip and the grain boundary has been studied. It was found that crack growth rate is strongly correlated to the dislocation pile-ups at the grain boundaries.