裂纹

Based on the foregoing analysis, the critical condition of realizing ductile/brittle transform is confirmed, and then, the model of ductile grinding of engineering ceramic is built.

以陶瓷材料压痕断裂力学、线性断裂力学和微观断裂物理学为理论基础，系统的分析和讨论了磨削加工过程中微裂纹的产生机理及其影响因素，建立了裂纹分布模型，并根据位错产生微裂纹机制，对磨削过程微裂纹的形成采用位错塞积模型来描述，从能量平衡的角度，讨论位错裂纹的稳定性与磨削应力的关系，确定了材料脆性去除和塑性去除转换的临界条件，最终建立以此为基础的工程陶瓷材料延性域去除模型。

In order to study the fatigue of pressure vessel commonly encountered problem in engineering with large destructibility , based on the theory of fracture mechanics , the pressure vessel existing original crack was equivalent to the problem of infinite flat with center crack .

为了分析工程中常见的破坏性极大的压力容器疲劳问题，基于断裂力学理论将存在初始裂纹的压力容器等效为无穷远处作用均匀拉应力的含中心裂纹无限大板问题，解出表面半椭圆裂纹和穿透裂纹的应力强度因子；利用断裂判据得到裂纹的临界断裂尺寸；采用Paris表达式对裂纹扩展速率进行描述，推导出初始裂纹在不同裂纹尺寸和形式下的裂纹疲劳扩展寿命。

Based on the fundamental principles of the improved method mentioned above, multi-functional computation software package, which can be used to analyze effectively the interference effects of random flaws in plane problem, boundary problem and space problem, is compiled and a number of problems involved in the interference effects of different kinds of flaws such as random equal length through-cracks, random branched throughcracks, random unequal length through-cracks, random holes to through-cracks, unequal length edge cracks, equal length and distance multiple edge cracks, random notches with different aspect ratio, random notch to edge crack, non-coplanar surface cracks with different aspect ratio, staggered surface cracks, surface crack to embedded crack and embedded cracks near free boundary are analyzed and computed by the package.

依据上述改进法的基本原理，本文编制了能有效地分析平面问题，边界问题及空间问题的任意缺陷群相互干涉效应的多功能计算软件包。据此，本文分析计算了各类缺陷群。诸如，任意等长裂纹群。任意折裂纹群；任意不等长裂纹群，任意孔与裂纹群，不等长边裂纹群。等长等间距多裂纹群，任意形状比缺口群，任意缺口与边裂纹，非共面不同形状比表面裂纹群，交错型表面裂纹群，表面裂纹与埋藏裂纹群及自由边界附近埋藏裂纹群等的相互干涉效应问题。

It includes hardware equipments and foundational theory of the image digitization. This paper expatiates on some digital image processing technologies that the inspecting system may apply to the research and analysis of the collected glass-crack image. Using neighborhood average method and median filter retrains the image noises and make the image edge smooth. Then protract the histogram of the gray image, get the threshold of this image, utilize the threshold method and gray-level slice method to get a binary image, and detect the image edge. Finally calculate the area and perimeter of the glass-crack image, and use the circularity to judge whether this image is a glass-crack image.

本文重点阐述了研究和开发这套玻璃瓶裂纹检测系统所应用到的一些数字图像处理技术，并应用这些技术和方法对采集的裂纹图像进行了处理和分析：应用邻域平均法和中值滤波法来抑制图像的噪声，使图像的边缘平滑；然后绘制出处理过图像的灰度直方图，得到该幅裂纹图像的阈值，利用阈值法和灰度级切片法对裂纹图像进行二值化处理，得到其二值图像，并对图像进行了边缘检测；最后计算出裂纹图像的面积和周长，利用圆形度指标来判断该图像是否为裂纹图像。

Crack propagation problems under the influence of the edges of the crack subjected to homogenous loads, the origin of the coordinates subjected to concentrated increasing loads, the central zone of the edges of the crack subjected to homogenous loads, the certain point of the edges of the crack subjected to moving unit step loads, the origin of the coordinates subjected to moving increasing loads Px m, the edges of the crack subjected to instantaneous impulse loads, the edges of the crack subjected to moving concentrated variable loads, the origin of the coordinates subjected to point loads, the edges of the crack subjected to a constant moving concentrated loads and the origin of the coordinates subjected to instantaneously moving impulse loads are studied respectively, and the analytical solutions of dislocation distribution function have been obtained.

同时对裂纹面受均布载荷、坐标原点受集中增加载荷、裂纹面中心区受均布载荷、裂纹面上某点受运动阶跃载荷、坐标原点受运动增加载荷Px m、坐标原点受瞬时冲击载荷、裂纹面受运动集中变载荷、坐标原点受集中载荷、裂纹面受常数运动集中载荷、坐标原点受瞬时运动冲击载荷作用下的裂纹扩展问题分别进行了研究，获得了位错分布函数的解析解。

These work are mainly based on two assumptions: one is called as the Deeg-Pak assumption, i.e., the crack is assumed to be an impermeable slit and thus the electric field inside the crack is equal to be zero; the other is called as the Parton assumption, i.e., a crack is treated as a permeable cut across that both the normal components of electric displacement and the tangential component of electric field are continuous.

裂纹问题：对于压电介质内的裂纹问题，近十年来人们已做了大量的理论分析工作，这些工作主要是基于两种假设：一种称之为 Deeg-Pak 假设，即假设裂纹为电非渗透的，因此裂纹内的电场等于零；另一种称之为 Parton 假设，即假设裂纹为电渗透的，且跨越裂纹上下表面电位移的法向分量和电场的切向分量是连续的。

In the case of granite, observation results indicate that the extending routes of active cracks are mainly intercrystalline, transcrystalline, inter-transcrystalline, and intracrystalline. When the strain rate is low, the long intercrystalline cracks are prevailing, and with increasing of the strain rate, the short transcrystalline and intracrystalline cracks gradually increase. The statistic results show that the active crack density increases with increasing of the strain rate, and the mean length of active cracks diminishes with increasing of the strain rate, that is, the induced damage in comminuted product increases with increasing of the strain rate. For the first time this dissertation integrates macroscopic results of comminution with active crack growth under impact loading. It elucidates why the dynamic comminution strength of mineral beds increases with increasing of the strain rate through the active crack extending, and analyzes the influence of structure and constitution of minerals on their damage under impact stress. It is authenticated that both the size distribution and the damage population of comminuted product can be characterized by the fractal.

为分析料层颗粒在冲击下的细观损伤效果，采用德国生产的ASM68K半自动图象分析仪对粉碎生成物中的损伤情形进行了观测，以花岗岩为例，观测结果表明花岗岩颗粒在冲击应力下的活化裂纹扩展路径主要表现为沿晶、穿晶、沿穿晶和晶内等形式，在低应变速率下，活化裂纹以沿晶裂纹较多，随着应变速率的提高，其它裂纹形式大量繁衍，统计结果表明活化裂纹密度随着应变速率的增大而增大，活化裂纹的平均长度随着应变速率的增大而减小，综合表现为颗粒的细观损伤程度随着应变速率的增大而增大；首次将应力作用下的活化裂纹演化特征与粉碎的宏观效果相联系，并就料层动态粉碎强度随应变速率增大而提高的现象从裂纹演化特征的角度进行了解释；分析了矿岩构造结构特性对损伤产生和分布的影响。

The coarsened structure perpendicular to primary crack plane exhibits better propagation resistance than that parallel with primary crack plane, but it seems that crack propagation property at high temperature can not be improved by changing γ′precipitates morphology.

颗粒形态不会改变裂纹扩展路径及微观机制，粗化结构的疲劳裂纹扩展阻力随温度升高而降低的趋势比原始结构剧烈，同时与主裂纹面垂直的粗化结构具有比与主裂纹面平行的粗化结构更好的疲劳裂纹扩展抗力，但通过改变γ′形态似乎不能改善高温下裂纹扩展性能。

It is clarified for the first time that the thermal fatigue failure of solder joint is actually a creep strain low cycle fatigue failure, and a physical model for creep fatigue crack propagation has been proposed. It was pointed out that creep strain increases in the high stress area ahead of the tip of thermal fatigue crack, results on one hand that the slide of crack tip increase, inactivation more serious and crack close length increases, the other hand, that intergranular crack exists, whose direction will affect the fatigue crack propagating.

本文首次阐明了焊点的热循环失效本质上是以焊点内循环蠕变为主要应变的低周疲劳失效，并在此基础上提出了蠕变疲劳裂纹扩展的物理模型，指出热循环裂纹前端的高应力区内，蠕变加剧，使裂纹前端滑移增加，裂纹钝化加剧，导致随后的裂纹闭合扩展长度增加；同时蠕变也使裂纹前端的高应力区出现晶间裂纹，蠕变沿晶裂纹对主裂纹扩展的影响取决于沿晶裂纹的连接方向。

The main research tasks and results are as follows:(1) Through comparing the stress intensity factor of compact tension specimen calculated by finite element software with the theoretical value, the feasibility of calculating fracture parameters of crack tip in ABAQUS software was verified.(2) The relationship between the elastic modulus of the material and research scale was studied based on deriving the cohesive stress theory and other relevant theories. And the elastic modulus of the material on meso-scale was determined.(3) Global model and sub-model of the finite element were built in th...e macro-scale, and stress-strain field nearby the crack tip was analyzed, and the results show that the detailed stress-strain in the crack tip could be obtained by using the sub-model technique.(4) In meso-scale, the crack growth model was also established by assuming the crack propagating along the grain boundary, and the detailed stress-strain field in the crack tip was obtained.(5) The effect of crack length on Von Mises stress, and maximum principal stress and strain was analyzed in meso-scale when equivalent KI equals 30MPa.m1/2. And the results show that except for crack tip area, the stress-strain distribution in whole specimen is not affected.

主要完成研究内容和取得成果如下：(1)利用有限元软件计算出紧凑拉伸试样的裂纹尖端应力强度因子KI值，其结果与理论值一致，从而验证了利用ABAQUS计算裂纹尖端相关断裂参量的可行性；(2)在研究内聚应力等相关理论的基础上，推导出了研究尺度与材料弹性模量的近似关系，并确定了介观尺度上的弹性模量；(3)在宏观尺度上建立了全局有限元计算模型和子模型，得到了裂纹尖端应力应变场分布，结果表明利用子模型技术获得比较准确的裂纹尖端应力应变场分布是可行的；(4)在介观尺度上利用平均晶粒尺度的方式建立了裂纹沿晶扩展模型，得到了裂纹尖端断裂过程区的微观应力应变场；(5)当应力强度因子为30MPa.m1/2时，分析了介观尺度上在裂纹沿晶扩展过程中裂纹长度对Mises应力、最大主应力和应变的影响，结果表明，裂纹扩展长度对试样整体应力应变分布影响不大，而对裂纹尖端区域有较大影响；(6)介。。。

According to the clear water experiment, aeration performance of the new equipment is good with high total oxygen transfer coefficient and oxygen utilization ratio.

曝气设备的动力效率在叶轮转速为120rpm～150rpm时取得最大值，此时氧利用率和充氧能力也具有较高值。

The environmental stability of that world - including its crushing pressures and icy darkness - means that some of its most famous inhabitants have survived for eons as evolutionary throwbacks, their bodies undergoing little change.

稳定的海底环境─包括能把人压扁的压力和冰冷的黑暗─意谓海底某些最知名的栖居生物已以演化返祖的样态活了万世，形体几无变化。