形变氮化20钢冲击断口的分形研究

利用垂直截面法测量了２０钢经不同形变和氮化复合处理后冲击断裂表面的分形维数。结果表明，材料的冲击功ＡＫ和沿裂纹扩展方向剖面Ｋｏｃｈ曲线的分形维数ＤＦ均随形变量的增加而增大。分形维数ＤＦ与ｌｎＡＫ之间呈正变化的线性关系，且满足关系式：ｌｎＡＫ＝６．３１３ＤＦ－４．９５１。     

Fe—Sb合金显微组织的分形描述

阐述了Ｆｅ－Ｓｂ合金显微组织的分形几何描述。Ｆｅ－Ｓｂ合金中α－Ｆｅ（Ｓｂ）相的形态可以用两个参数来描述：分形维数Ｄ和形状因子ＳＤ。     

无机膜的分形性

介绍了无机膜的分形性和物体的三种重要分形．在溶胶－凝胶（Ｓｏｌ－Ｇｅｌ）制无机膜的工艺中，胶粒通过生长聚集方式成膜，它受质量分形规律控制，可以通过测定质量分形维数，利用ＤＬＡ、ＤＬＣＡ、ＲＬＣＡ等数学模型定量描述Ｓｏｌ－Ｇｅｌ膜生长的形态构造及对孔结构的影响．同样，在注浆及浸涂工艺制微孔基质膜工艺中，粉体以桥接堆积，存在孔结构分形，可通过测定孔分形维数定量描述这种在三维空间下高度复杂的孔结构．     

PBTCA稳定Al_2O_3悬浮液及沉积物分形特性的研究

测定了２－膦酸丁烷－１;２,４－三羧酸（ＰＢＴＣＡ）的电离特性,并通过Ｚｅｔａ电位、粒径分布、沉降、比表面积等手段研究其在Ａｌ２Ｏ３表面的吸附及其对电动特性和稳定性的影响．结果表明;ＰＢＴＣＡ在Ａｌ２Ｏ３表面发生化学吸附,并能显著提高颗粒表面的带电量,从而改善浆料的稳定性．ＦＴＩＲ研究表明;羧基及磷酸基均参与了ＰＢＴＣＡ在Ａｌ２Ｏ３表面的化学吸附,从而提高了吸附强度．通过对沉积物表面ＳＥＭ照片的灰度分析发现,其表面形貌具有分形特征,且悬浮液的稳定性越好,沉积物表面的分维值Ｄｆ越大．     

聚碳酸酯改性环氧树脂的结构与性能

采用ＤＳＣ，ＤＭＡ，ＦＴＩＲ和ＳＥＭ等方法研究了ＰＣ／Ｅ５１／ＴＥＰＡ和ＰＣ／Ｅ５１／ＤＤＳ两种共混体系的经、结构特征、力学和热性能。实验表明：体系的固化反应可按原位固化方式进行，ＰＣ对固化反应起促进作用。共混体系具有均相结构特征，两组份间存在有较强的氢键作用，从而提高了体系的Ｔｇ，模量、密度和热稳定性。ＰＣ／Ｅ５１／ＴＥＰＡ样品透明，两个体系对冲击韧均略有改善。     

人GM－CSF在链霉菌中的表达

报道了ＰＩＪ４５９／ＧＭ－ＣＳＦ基因表达质粒的构建，以及该重组质粒在变铅青链霉菌Ｓ．ｌｉｖｉｄａｎｓＴＫ５４中的表达，结果表明：ＰＩＪ４５９／ＧＭ－ＣＳＦ质粒具有表达ｈＧＭ－ＣＳＦ的功能。重组菌株细胞裂解液经ＴＦ－１细胞培养及集落形成实验均证实了其生物学活性。并分析了影响外源基因表达的某些因素，如ＳＤ序列与ＡＴＧ之间的距离，时间对表达的诱导等，探讨了外源基因高效表达的适宜条件。     

多相材料断裂的分形特征

测量了多相材料复合涂层的断裂挠度和断口表面的分形维数，分析了复合涂层的断裂特征。结果表明：随着硬质相增加，复合涂层的断裂挠度和断口表面的分形维数降低。     

分形维数与D6AC钢的韧性

本文研究了超高强度钢Ｄ６ＡＣ的断裂韧性、冲击韧性和拉伸面缩率与断口分形维数的关系。分别用二次电子线扫描和数字图像法断裂韧性试样的断口分形维数，得出试样的韧性与分形维数Ｄｓｅ，ＤＨ和ＤＬ成正比关系，即韧性随分形维数增大而增加。试样断口的粗糙度由夹杂物引起差异小于金相组织不同引起的差异时，使用数字图象法测得的分形维数与韧性的线性关系优于二次电子线扫描的结果。     

企鹅最新系列产品介绍

企鹅最新系列产品介绍丁一企鹅公司自９４年在国内推出了普及型２０５、２０５Ｄ、Ｋ９１０、Ｋ９１０Ｄ、中档型ＦＡＳＢ、ＦＡＳＢＤ、ＫＭ８８０、ＫＭ８８０Ｄ、高档型ＦＡｇＮ、ＦＡｇＮＤ系列相机之后，在第六届中国照相机械产品博览会上又推出了３０５、３０５Ｄ、...     

包装与市场营销环境

包装与市场营销环境王润球ＰＡＣＫＡＧＩＮＧＡＮＤＥＮＶＩＲＯＮＭＥＮＴＯＦＭＡＲＫＥＴＳＡＬＥＳ￥ＷａｎｇＲｕｎｑｉｕＡｂｓｔｒａｃｔ：Ｉｎｍｏｄｅｒｎｃｏｍｍｏｄｉｔｙｅｃｏｎｏｍｙ，ｐａｃｋａｇｉｎｇｉｓａｎｏｒｇａｎｉｃｐａｒｔｏｆｃｏｍｍｏｄ...     

Three-Dimensional Analyses by Finite Element Method of a Spur Gear: Effect of Cracks in the Teeth Foot on the Mesh Stiffness

In this paper, a finite element method with a three-dimensional survey is presented. The effect of crack dimension and the direction of crack propagation, in the teeth foot, on the mesh stiffness is studied. For spur gears, the mesh stiffness is affected in a meaningful manner by the presence of a foot crack of one or more teeth. This study is an attempt to estimate the effect of crack size, position, and direction on the spectrum of the gear mesh stiffness.     

The effect of a pre‐existing crack on a running crack in brittle material under dynamic loads

Brittle material usually contains plenty of cracks or micro‐cracks, which raises a question that how a pre‐existing crack affects a running crack as they are approaching. In order to investigate such issue, impact experiments were conducted by using double crack semi‐circle (DCSC) specimens. Polymethyl methacrylate (PMMA) was selected to make the DCSC specimens, and a modified SHPB system was used to perform the impact tests. The finite difference code AUTODYN was employed to simulate the crack propagation behavior and propagation path, and the simulated crack paths agree well with the impact test results. Meanwhile the stresses around the crack tips were analyzed and the crack propagation direction was investigated. To calculate the crack dynamic stress intensity factors (DSIFs), finite element code ABAQUS was employed. The results show that the spacing D between the vertical crack tip and the inclined crack center affects the stress distribution and fracture behavior of the vertical crack largely. As the vertical crack approaches the inclined crack, the crack speed is slow down, and tensile stress appears at the inclined crack tip. As the spacing D is small than 50 mm, the vertical crack connects with the middle area of the inclined crack. As the spacing D is 50 mm, the vertical crack connects with either the middle area or the upper tip of the inclined crack. As the spacing D is larger than 50 mm, the vertical crack coalesces with the upper crack tip.     

基于分形理论不同装药量的爆破动焦散线实验研究

为研究装药量对爆生裂纹扩展行为的影响。采用透射式数字激光动态焦散线实验系统,分析了不同装药量的爆生裂纹扩展规律,并基于计盒维数的计算原理,编写MATLAB程序计算爆生裂纹的分形维数。结果表明:①起爆后裂纹扩展分2阶段,Ⅰ阶段(0～114.3μs)为爆炸应力波与爆生气体对裂纹尖端的作用,在裂纹的起裂时刻扩展速度达到峰值,随即迅速降低;Ⅱ阶段(114.3μs～裂纹止裂)在反射应力波对裂纹尖端的作用下,裂纹扩展速度继续提升;②裂纹扩展速度峰值、动态应力强度因子峰值、粉碎区面积、爆生裂纹分形维数与装药量正相关;③采用回归分析与线性拟合的方法,得到了裂纹扩展速度与裂纹扩展轨迹分形维数的线性关系,同一裂纹扩展速度的变化符合分形规律。     

Finite-element modelling of crack propagation in elastic–plastic media: Part II Horizontal subsurface cracks

Horizontal subsurface cracks in an elastic–plastic material are analysed using finite-element techniques. The sliding surface is modelled as a rigid cylinder. The effect of such parameters as the friction between the cylinder and the material being indented, the elastic and plastic modulus of the material and the depth of crack location on the J-integral values at the left and right tips of a horizontal subsurface crack is considered. The prospective crack propagation direction is taken as the direction along which the J integral assumes a maximum as the indenter slides along the material surface. The left and right tip cracks were found likely to propagate at about 10° to the horizontal. This propagation direction was found to depend strongly on the location of the crack. Both crack tips are expected to propagate closer to the vertical direction as the depth of crack location is reduced. Also, horizontal cracks closer to the surface are found to have higher J integral values. While friction between the slider and the specimen did not affect the crack propagation direction, the crack-tip plasticity reduced the propagation direction, with respect to the horizontal.     

Influence of microscopically distributed inhomogeneity and anisotropy of grains on high-temperature crack propagation properties of directionally solidified superalloy

The fluctuation of J-integral, during high-temperature fatigue crack propagation, due to the microscopic inclination of crack and elastic anisotropy of each grain, is investigated by means of a series of finite-element-analyses on a cracked body. The simulated material is a nickel-based directionally solidified (DS) superalloy, where the DS axis, load direction, and crack propagation axis are set to be perpendicular to each other. The magnitude of J is estimated using two-dimensional models simulated after an experimental test: (i) with the actual crack shape and grain arrangement, (ii) with the actual crack shape in a homogeneous body, and (iii) with a straight crack in a homogeneous body (averaged deformation behavior of the material). The microscopic inclination of crack propagation direction causes the sporadic drop of J at the point where the crack direction is largely inclined from the direction normal to the load axis. The anisotropy of grains causes the stepwise change in the a (crack length) vs. J relationship. Such changes in J due to the microscopic inhomogeneity directly relates to the change of the crack propagation rate in the transgranular cracking. Then, J, which takes into accounts the anisotropy of grains, correlates well with the crack propagation rate in the transgranular cracking. The grain-boundary cracking possesses fluctuated J, and shows weaker resistance to the propagation than the transgranular one.     

FATIGUE CRACK GROWTH UNDER MODE II LOADING

Abstract— The behavior of fatigue crack growth for low and medium carbon steels, an austenitic stainless steel and an aluminum alloy under pure Mode II loading was investigated experimentally, using cruciform specimens. The results show that under pure Mode II loading, fatigue crack propagation has three possibilities, namely, bifurcation into two branches, propagation along the original Mode II direction, and the mixture of these two situations, depending on the material. The growth rate da/dN vs. ΔK_II relation for Mode II propagation is similar to a Pans type law for Mode I growth. Fractographic observations by optical microscopy and SEM were made also on all specimens tested. When a crack branched, striations parallel to the crack front which were often associated with Mode I fatigue crack growth were observed and long marks parallel to the crack propagation direction were also found for slanted fracture surfaces. When a crack propagated along the original Mode II direction, many frictional marks parallel to the crack propagation direction were observed.     

氢致裂纹慢扩展区断裂表面的分维研究

用垂直剖面法测量了一种含氢高强度钢在静弯矩作用下由裂纹慢扩展形成的断裂表面不同部位的分维 D,发现 D 随断裂表面塑性成分的增加而增加。在平面应变条件下,裂纹慢扩展形成断裂表面的过程是一个增维过程,当分维达到某一临界值时,裂纹失稳扩展。     

Simulation of the shear-tensile mode transition on dynamic crack propagations

We propose an approach to the simulation of the shear-tensile transition in dynamic crack growth based on two points: a new crack propagation criterion which is suitable for shear, and an algorithm which is capable of handling the transition from shear mode to tensile mode and back in the same simulation. The new crack propagation criterion for brittle crack growth is based on the maximum shear stress rather than the maximum hoop stress. The shear stress direction becomes the new crack??s direction in which propagation is initiated for shear-type failure. The stress state at the crack??s tip is obtained through a local approach which can be used even in the case of extensive plasticity. Additionally, we propose to control the transition from shear mode to tensile mode during the simulation of crack propagation using an equivalent strain estimated at the crack??s tip. Depending on a threshold strain, the propagation direction is predicted using the maximum shear stress (in the shear case) or the maximum hoop stress (in the tensile case).     

Ti6321合金的拉-扭疲劳行为研究

通过Ti6321合金的拉-扭疲劳试验,对0°和30°相位差的疲劳寿命进行对比分析,研究0°相位差时微裂纹和宏观裂纹扩展路径,并对疲劳断口进行分析.结果表明:相同Mises等效应力幅下,相位差为30°时疲劳寿命相对相位差为0°时的较低;受切应力主要作用,Ti6321合金表面萌生的微裂纹绝大部分分布在与试样轴向夹角20°～...