汽轮机调速器壳体焊缝裂纹原因分析与修理

通过对岳阳纸业股份公司热电厂 C1 2 - 35 / 1 0型汽轮发电机组调速器壳体焊缝裂纹原因的分析 ,用壁厚加强的修理办法 ,从根本上解决了补焊无效的问题 。

弧焊机器人焊炬姿态规划系统的研究

为提高弧焊机器人的适应性和自动规划功能 ,研究了一种空间全位置焊接条件下的焊炬姿态自动规划系统。该系统借助于相应的摄像机标定软件、计算测试软件和焊炬姿态规划软件 ,协调计算机视觉、信号采集、图像处理等模块检测焊缝的空间信息 ,然后查询焊炬姿态优化数据库 ,运行离线编程等子模块 ,实现自动规划弧焊机器人的焊炬姿态。采用研制的焊炬姿态规划系统在空间全位置条件下进行焊接实验 ,结果表明 ,该系统能保证焊接中焊缝的成形良好。

RTS─300型轮式探头超声波检测设备在Φ508mmERW机组上的应用

介绍了该厂从美国ＤＡＰＣＯ公司引进的ＲＴＳ－３００型超声波探伤设备的结构、特点及其在Φ５０８ｍｍＥＲＷ机组生产线上焊缝探伤的应用。

Fractal characteristics of cracks and fragments generated in unloading rockburst tests

True triaxial rockburst experiments with four different unloading rates were performed on four prism specimens of granite sampled from Beishan, China. The damage evolution in the rockburst test was investigated from two aspects including fracture surface crack and fragment characteristics. The scanning electron microscopy was used to observe the micro crack information on fragment surface. Combing binarization and box counting dimensions, the fractal dimensions of cracks were obtained. Meanwhile,the fragments were collected and a sieving experiment was conducted. We weighed the fragments qualities, counted the amount of fragments and measured the fragments length, width and thickness.Utilizing four methods to calculate damage fractal dimensions of fragments, the trend of fractal value changing with unloading rates can be roughly described. It can be concluded from these experiments that the fractal dimension either for crack or for fragment holds a decreasing trend with the decreasing unloading rate, indicating a reduction of damage level.

Sutureless Intestinal Anastomosis with a Novel Device of Magnetic Compression Anastomosis

Objective To explore the feasibility and efficiency of a novel magnetic compression anastomats(MCAs) in intestinal anastomosis.Methods A total of 36 male mongrel canines underwent intestinal anastomosis using traditional hand-sewn(n=18) or a novel MCAs(n=18).We compared the anastomosis time,postoperative complications,bursting strength of anastomoses,gross appearance,and pathology between two groups at each time-point of follow-up.Results The mean anastomosis time with MCAs was significantly less than that with hand-sewn(8.50±1.95 vs.31.1±4.32 minutes,P<0.001).The blood stools and intussusceptions occurred in both groups during follow-up period.Only 1 mongrel canine receiving intestinal anastomosis by MCAs experienced anastomotic leakage.The average bursting pressure of anastomoses obtained from mongrel canines undergoing intestinal anastomosis by MCAs was significantly higher than that by traditional hand-sewn at 1 week's follow-up time(P<0.05).Gross appearance of the anastomoses constructed by MCAs was relatively smoother and flatter.Pathological evalution of anastomoses revealed that general inflammation was greater in hand-sewn anastomoses than magnetic anastomosis.Conclusion The magnetic compression anastomat is a safe and effective device of sutureless intestinal anastomosis in canine models.

Numerical study on crack propagation under explosive loads

Dynamic crack propagation in brittle materials plays an important role in unJerstanding the fracture mechanism.Numerical simulations on crack propagation in the polymethyle methacrylate(PMMA)under explosive loads were carried out through Autodyn 3D code.Although the Johnson-Holmquist(JH-2)constitutive model has been widely treated as an acceptable scheme,it cannot improve the description in the post-failure response of material and reduce the mesh dependency,so the crack softening failure model are introduced in our present work based on two failure criterions.First,material parameters of JH-2 model,failure criterion,and crack softening failure model are determined from available data and calculations.The circular and rectangle thin plates are modeled to explore the fracture mechanisms for single-borehole and dual-borehole explosions.The simulation results well reproduced the entire dynamic evolutionary process of the crushed and fractured zones,crack initiation,propagation and arrest as well as secondary propagation,which successfully proved the relibilities of the combination of JH-2 constitutive model,failure criterion,and crack softening failure model and corresponding material parameters.For dual-borehole explosion,the crack linkage is well performed when borehole distance L is 20 and 30 cm;cracks are failed to link with each other at L=40 cm although main cracks have arrived into the opposite fractured zone.More importantly,it is found that the crack linkage mainly depends on L,which has an important effect on linkage style and its location.Despite a larger L makes more difficult in crack linkage,this difficulty lies not in the shortage of crack length,but in losing control of directional fracture of cracks between two boreholes.

Numerical study on explosion-induced fractures of reinforced concrete structure by beam-particle model

In the field of disaster prevention mitigation and protection engineering,it is important to identify the mechanical behaviors of reinforced concrete(RC)under explosive load by simulation.A three dimensional beam-particle model(BPM),which is suitable to simulate the fracture process of RC under explosive load,has been developed in the frame of discrete element method (DEM).In this model,only the elastic deformations of beams between concrete particles were considered.The matrix displacement method(MDM)was employed to describe the relationship between the deformation and forces of the beam.A fracture criterion expressed by stress was suggested to identify the state of the beam.A BPM for steel bar,which can simulate the deformation of steel bar under high loading rate,was also developed based on the Cowper-Symonds theory.A program has been coded using C++language.Experiments of RC slab under explosive load were carried out using the program.Good agreement was achieved between the experimental and simulated results.It is indicated that the proposed theoretical model can well simulate the fracture characteristics of RC slab under explosive load such as blasting pit formation,cracks extension, spallation formation,etc.