基于X射线CT的岩石内部裂纹宽度测量

岩石内部裂纹变形、扩展和扩张是试样在裂纹演化阶段的主要过程。研究基于X射线CT的岩石内部裂纹宽度测量问题,根据岩石变形破坏的细观机制,分析了岩石密度损伤与体应变的关系。对脆性岩石来说,岩石的体积变形与其密度损伤有一一对应关系。基于X射线密度损伤增量公式,推导出岩石体应变公式,得到岩石内部裂纹宽度的普适性计算公式。据此测得岩石中两条CT尺度裂纹在不同应力阶段的宽度,并与有关公式进行了比较,相互得到验证。说明在动态条件下岩石内部裂纹宽度测量问题在理论上可以得到解决。

X65煤层气焊管变形开裂原因分析

在检修现场发现X65煤层气焊管存在非正常变形量及裂纹。本文通过化学分析、力学性能检测、金相分析、仪器化压痕法检验等方法进行了分析,经过排除法论证和现场确认,由于直缝焊管的抗拉强度比螺旋焊管的抗拉强度高,山体滑坡造成施工现场公路填方土蠕动变形,蠕动变形对公路附近管道造成巨大轴向推力,当此轴向外力超过管道本身的屈曲载荷时,进而造成管道失稳变形。

DSCM测量铸铁裂纹尖端演化过程

基于梯度的搜索算法计算亚像素位移、基于位移场局部最小二乘拟合计算应变场.测量了铸铁预制裂纹三点弯曲梁裂纹尖端的演化过程,给出了试件加载过程中的全程荷载-位移曲线以及试件裂纹扩展的过程.由DSCM分析结果,给出了试件在不同加载阶段下裂纹尖端的位移场及应变场.

Macro-meso fracture evolution mechanism of hollow cylindrical granite with different hole diameters under conventional triaxial compression

In order to study and analyze the stability of engineering rock mass under non-uniform triaxial stress and obtain the evolution mechanism of the whole process of fracture,a series of conventional triaxial compression tests and three-dimensional numerical simulation tests were carried out on hollow granite specimens with different diameters.The bearing capacity of hollow cylindrical specimen is analyzed based on elasticity.The results show that:1)Under low confining pressure,the tensile strain near the hole of the hollow cylindrical specimen is obvious,and the specimen deformation near the hole is significant.At the initial stage of loading,the compressive stress and compressive strain of the specimen are widely distributed.With the progress of loading,the number of microelements subjected to tensile strain gradually increases,and even spreads throughout the specimen;2)Under conventional triaxial compression,the cracking position of hollow cylinder specimens is concentrated in the upper and lower parts,and the final fracture mode is generally compressive shear failure.The final fracture mode of complete specimen is generally tensile fracture.Under high confining pressure,the tensile cracks of the sample are concentrated in the upper and lower parts and are not connected,while the cracks of the upper and lower parts of the intact sample will expand and connect to form a fracture surface;3)In addition,the tensile crack widths of intact and hollow cylindrical specimens under low confining pressure are larger than those under high confining pressure.

铸带上下表面裂纹分布不均的原因分析

双辊薄带连铸方法生产的铸带上下表面裂纹分布不均匀,呈现上表面多而下表面少的现象。本文从热力学角度对该现象进行分析,说明上表面较大的温度梯度使其更易于产生裂纹;从铸带变形的角度进行分析,发现上表面有较大的变形量,该变形量大小与弧形板的形状及铸带所受外力有关,这也使其上表面易于产生裂纹。有别于以往对裂纹这一现象的研究,本文不关心裂纹形成的先天因素,而是通过对铸带后天环境的分析,提出在熔池之外减少裂纹的新思路。

熔模铸件热裂纹缺陷的分析与实践

热裂纹是熔模铸件常见的裂纹变形类缺陷之一。生产中铸件产生热裂纹的废品率高（有时高达15％～20％），不仅增加了产品成本，甚至影响了正常的生产周期和交货期，严重地影响了企业的经济效益。因此，如何预防、减少，甚至消除热裂纹缺陷，是熔模铸造工作者的重要课题之一。

有限变形下线弹性裂尖场的渐近分析

对有限变形下线弹性Ⅰ型裂纹场建立了无需分区的统一控制方程并进行了浙近分析,利用“打靶法”得到位移场在物质描述与空间描述下的渐近阶次分别为3/4和1,Green应变、第二类P-K应力及Cauchy应力在物质描述与空间描述下的渐近阶次分别为-1/2和-2/3;对不同泊松比,裂尖有限变形线弹性场的位移均以U_Ⅱ或u_2为主导,裂纹张开角为π,现时构形中的大变形区为一垂直初始构形中裂纹表面的狭长带状区,应力则处于由σ_(22)主导的单向拉伸状态,角分布函数U_Ⅱ及σ_(22)(0)具有奇异性,但U_L/U_Ⅱ(0)及σ_(ij)(θ)/σ_(22)(0)均趋于有限值。

球磨机入口端盖裂纹原因分析及处理

介绍了某电厂球磨机入口端盖出现大面积裂纹损坏问题,通过对磨机造成裂纹原因分析,提出针对性对策,并重点阐述了处理过程中的技术要求以及问题解决方法,希望能够为同类型设备问题处理提供帮助。

燃气电站锅炉炉墙裂纹产生原因和解决对策

某铁合金厂为保护环境和节约能源，利用高炉煤气发电，锅炉型号为QC22-20-2.45/400（配3000kW汽轮机机组），设计给水温度105℃，预热空气温度262℃，排烟温度172℃，累计连续运行68000h。2004年初发现炉墙前、左、右3面轻微裂纹变形,2005年发现炉墙有多处较严重裂纹变形,测量炉墙温度在60～85℃，高于锅炉炉墙设计温度（要求低于40℃）。

浅谈砖砌体结构房屋的变形裂缝

本文在简要总结分析砖砌体变形特征和规律的基础上 ,提出几点治理措施。

Failure mechanism of as-cast Mg-6Zn-2Er alloy during tensile test at room temperature

Tensile test of the as-cast Mg-6Zn-2Er alloy was conducted at room temperature. The results indicate that the alloy is inclined to failure when the strain reaches 5.6%. The coarse secondary phases are responsible for the failure, especially for the Mg3Zn3Er2 phase （W-phase）. It is indicated that the existence of the W-phase activates the stress concentrations due to the incapacity of W-phase for the load transfer, which results in the void at the inner of the W-phase. In comparison, the interface between the matrix and the secondary phase is stable. In conclusion, the characters of the secondary phases with respect to size, distribution, morphology and type, play an important role in the plastic deformation behavior of the alloy.

小型飞机铝合金结构修理简析

随着我国通航产业的迅速发展,小型飞机在我国保有数量突飞猛涨。在飞机使用过程中,随着飞机使用时间的增加,飞机结构受力部附件由于意外碰撞损伤(如重着陆、鸟击)、或金属结构件疲劳等影响,结构故障问题已经突显,其主要表现有蒙皮变形、破孔、裂纹等损伤,以及受力结构件(如翼肋、桁条、梁、隔框等)变形、裂纹、缺损等损伤。小型飞机铝合金结构主要功能为维持气动外形、承载、及传递载荷等,主要保障飞机的飞行安全。本文参照Cessna172R型飞机结构修理手册相关程序规范,对小型飞机铝合金结构修理进行简析,通过对飞机结构损伤等级分类、损伤形式及典型损伤修理类型进行分析,可提高对飞机铝合金结构损伤认识,以及小型飞机金属结构损伤维护的可靠性,保证飞机运行安全。

Equivalent elastic compliance tensor for rock mass with multiple persistent joint sets:Exact derivation via modified crack tensor

Discontinuities constitute an integral part of rock mass and inherently affect its anisotropic deformation behavior.This work focuses on the equivalent elastic deformation of rock mass with multiple persistent joint sets.A new method based on the space geometric and mechanical properties of the modified crack tensor is proposed,providing an analytical solution for the equivalent elastic compliance tensor of rock mass.A series of experiments validate the capability of the compliance tensor to accurately represent the deformation of rock mass with multiple persistent joint sets,based on conditions set by the basic hypothesis.The spatially varying rules of the equivalent elastic parameters of rock mass with a single joint set are analyzed to reveal the universal law of the stratified rock mass.

Low-cycle fatigue behavior of K416B Ni-based superalloy at 650 ℃

A study on the low-cycle fatigue(LCF)behavior of K 416 B alloy was conducted at 650℃.According to the results,the LCF behavior of K 416 B alloy at 650℃ is mainly manifested as elastic deformation and the fatigue life of the alloy is determined by the level of material strength.When tension-compression fatigue occurs,the deformation mechanism of the alloy is reflected in the form of dislocation slip,and the deformation dislocations are bowed out in the matrix by Orowan mechanism,which leads to a dislocation configuration similar to the Frawk-Reed source.At the late stage of low-cycle fatigue,the fatigue-induced cracks develop from the alloy surface.As fatigue test proceeds,it is possible for the cracks to continue development along the regions of eutectic and the bulk M 6 C carbide due to stress concentration,thus causing the alloy to show cleavage fracture.

Effects of pre-rolling on mechanical properties and fatigue crack growth rate of 2195 Al-Li alloy

While pre-deformation is often conducted before aging treatment to increase the strength and microhardness of 2195 Al-Li alloy, it often increases the fatigue crack growth(FCG) rate and thus reduces the fatigue life of the alloy.To determine the effects and causes of pre-deformation and heat treatment on the mechanical properties and FCG rate of2195 Al-Li alloy, and to provide a suitable calculation model for the FCG rate under different pre-deformation conditions, 2195 Al-Li alloy specimens with different degrees of pre-rolling(0, 3%, 6%, and 9%) were investigated. The experimental results indicate that with the increase of pre-rolling, the density of the T1phase and the uniformity of the S′distribution and the microhardness, tensile strength, and yield strength of the alloy increase and at the same time the FCG rate increases, and thus the fatigue life is reduced. It was also found that the normalized stress intensity factor of elastic modulus(E) can be applied to correlate the FCG rate of pre-rolled 2195 Al-Li alloy with constant C and K parameters.

Evaluation of Energy Saving Operational Modes for Industrial Fracture Connected Processes on the Basis of Incubation Time Fracture Criterion

A problem for a central crack in a plate subjected to plane strain conditions is investigated. Mode I crack loading is created by a dynamic pressure pulse applied at a large distance from the crack. It was found that for a certain combination of amplitude and duration of the pulse applied, the energy transmitted to the sample has a strongly marked minimum, meaning that with the pulse amplitude or duration moving away from the optimal values, minimum energy required for initiation of crack growth increases rapidly. The results obtained indicate a possibility to optimise energy consumption of different industrial processes connected with fracture. Much could be gained in, for example, drilling or rock pounding where energy input accounts for the largest part of the process cost. Presumably further investigation of the effect observed can make it possible to predict optimal energy saving parameters, i.e. frequency and amplitude of impacts, for industrial devices, e.g. bores, grinding machines, and hence significantly reduce the process cost. The pre- diction can be given based on the parameters of the media fractured （material parameters, prevalent crack length and orientation, etc.）.

SFNCM1080S高强钢花键轴完全断裂的修复工艺

介绍了SFNCM1080S高强钢花键轴完全断裂后修复存在的技术难点,分析了焊接过程中修复的关键技术,并针对性地提出了工艺方案。通过选用与母材等强且合金成分相近的焊材、优化热处理工艺参数、设计对接坡口形式及焊接顺序、采取轴变形控制措施,成功地完成了断裂轴的所有修复工作,有效地控制了裂纹的产生及焊接变形。花键轴经受了80%负荷连续运行3个多月的考验,直至新轴采购到位进行更换,为企业挽回了巨大的经济损失。

橡胶摩擦和磨耗的统一物理概念(一)--橡胶新的摩擦基本原理和新的摩擦理论

作者对橡胶摩擦提出了一种新的基本原理和理论,这与以往的理论有很大的不同。总摩擦系数包含3个因素:附着项μs、变形项μ和裂纹形成项μcrac,这将形成如下方程式:μall=μadh+μdef+μcrac≌μadh[1+K2(tanδ/√2+√2Kεc)E^(-7/6W^(1/6)]式中:μ为非交联相的粘度;E为交联橡胶的模量;V为滑移速度;C为裂纹长度;W为正常负荷:K1、K2、Kε均为系数。在橡胶摩擦过程中,作为零的近似值,附着项是最主要的因素,约占总摩擦系数的70%~80%。新理论对速度和正常载荷与橡胶摩擦系数的关系的解释是相当合理的,这与在橡胶与固体界面之间形成半月形密切相关。

一种针对裂尖变形场测量的正则化全局DIC方法

裂纹尖端变形场测量是定量研究材料断裂特性和行为的关键。基于子区的局部数字图像相关(Digital Image Correlation,DIC)目前应用较多,但跨裂纹子区计算出的数据并无意义,且在测量复杂裂纹变形场时会面临欠匹配的问题。为了克服这些缺点,提出一种基于Hermite单元的正则化全局DIC(HRGDIC)方法。该方法采用高阶Hermite形函数构建全局DIC的有限元单元,建立同时考虑灰度误差与位移场光顺性的迭代方法。同时,在每次迭代求解的过程中使用广义交叉验证(GCV)方法来求解最优正则化参数。于是,HRGDIC方法不仅能处理尖端复杂高梯度变形,还可在迭代结束时获得平滑的位移场和应变场。从裂纹尖端变形图像的模拟和真实测量结果可知,与传统的局部DIC方法相比,所提方法测量精度更高,是解决裂纹尖端变形场测量的有效方法。

针对裂尖变形场测量的包络单元局部数字图像相关方法

使用数字图像相关(DIC)方法测量平滑、准确的裂纹尖端位移场和应变场是学术界难题之一。目前常用的方法为基于子区的局部DIC方法,但其子区跨裂纹计算的结果无意义。经过改进的基于子区分割的DIC方法降低了子区内像素点数量,导致精度降低。提出一种基于Hermite单元的局部DIC(HELDIC)方法,依次分块计算感兴趣区域(ROI),利用较大单元包络分块区域剔除单元边界精度较低的数据,通过调整Hermite单元位置使得剔除的数据量最少,再使用所提改进的逐点最小二乘(PLS)方法平滑分块的位移场并得到应变场,从而提高裂纹尖端应变场的平滑度和精确度。实验结果表明,所提方法与传统局部DIC方法相比获得的变形场距离裂纹尖端及裂纹面更近,且在给定的单元和子区大小下的应变场平均误差降低30%以上,是计算裂尖变形场的有效方法。