锅炉减温器喷水管失效原因分析

通过宏观检验、电镜观察和理论计算,对同时承受机械应力和热应力的锅炉减温器喷水管失效断口形貌进行分析,研究其断裂模式与原因。结果表明,该喷水管断裂属于于热-机械疲劳断裂,交变弯曲应力和热应力是其断裂失效的主要原因。热应力使管内壁产生浅表性热疲劳裂纹,并导致机械疲劳裂纹稳定扩展至该区时发生局部快速扩展,产生局部快速断裂区,其形貌不同于常规疲劳断口最后瞬断区。     

锅炉捞渣机链环断裂原因分析

通过断口宏观形貌观察、化学成分分析、拉伸性能和冲击性能试验、硬度测试、断口微观形貌观察和金相组织检查等方法,对锅炉捞渣机链环断裂的原因进行了分析。结果表明:捞渣机链环的失效类型为疲劳断裂。在捞渣机运行过程中,链环弯弧段内侧近表面在残余拉应力和拉弯疲劳载荷的作用下被反复挤压磨损,晶界微裂纹在链环弯弧段内侧近表面萌生和扩展,直至断裂。     

煤粉细碎机转轴断裂原因分析

某电厂碎煤系统细碎机在运行过程中发生转轴断裂失效。为查明煤粉细碎机转轴断裂原因,利用外观形貌分析、化学成分分析、断口微区分析、力学性能检测及显微组织检测等方法,对断裂的细碎机转轴进行综合性检测分析。结果表明该煤粉细碎机转轴变截面未设置倒角且加工粗糙,存在应力集中情况;细碎机转轴未进行调质处理,抗拉强度及屈服强度低于标准要求;运行过程中,在循环扭转载荷作用下,变截面的应力集中部位产生裂纹缺陷,并快速扩展引发轴体疲劳断裂。     

给水泵汽轮机动叶片微动磨损疲劳断裂的失效特征分析

某超超临界600 MW机组给水泵汽轮机第2级动叶片在投产初期就发生微动磨损疲劳断裂失效,对此通过故障现场检查,分析断裂叶片的材质和断口形貌,采用有限元计算分析叶片离心应力,以及综合分析叶轮叶片系统振动特性,得到微动磨损疲劳断裂失效的特征及原因。分析认为:动叶片的微动磨损疲劳断裂均起源于叶根第1齿工作面,第1齿工作面和叶顶一侧表面存在轮胎印型擦痕、磨损斑点、表面发亮及小裂纹等磨损痕迹,第1齿工作面截面存在多条呈分层的裂纹,源区的微观组织和硬度与基体相比明显异常,齿面和断口一般无腐蚀性元素;引起第2级动叶片微动磨损疲劳断裂失效的原因为装配质量不良。     

超超临界机组锅炉减温器典型失效案例分析

喷水减温器是目前超超临界机组重要的汽温调节方式,通过对近几年超超临界机组中出现的典型减温器结构(包括旋涡式、多孔喷嘴式以及莫诺克式等)失效案例进行分析,研究造成其断裂失效的机理。结果发现:低温减温水与减温器喷嘴之间温差大,导致减温器喷嘴产生巨大的温差热应力是造成减温器出现裂纹的主要原因。低温减温水投用频繁,造成减温器内壁出现骤热骤冷的交变应力,加快了减温器的热疲劳失效。另外,部分减温器设计不合理,如喷水管存在膨胀受阻、结构突变或与集箱存在横向间隙,从而导致喷水管振动加剧产生机械疲劳开裂,这也是某些结构的减温器失效的重要原因。     

超超临界机组水冷壁管弯曲处失效泄漏原因分析

采用化学成分分析、硬度检测、金相观察、扫描电镜断口分析、断口表面腐蚀产物的能谱分析以及有限元数值模拟等手段,对某发电公司的水冷壁管失效泄漏的原因进行了分析。结果表明:水冷壁制作过程冷变形所致的残余应力和运行过程的热应力过大,是导致管子弯曲处过早失效的主要原因,腐蚀烟气对热疲劳裂纹扩展起了促进作用。     

600MW机组次末级叶片失效断裂原因分析

通过化学成份、力学性能、金相组织、扫描电镜表面形貌测试,对某厂600 MW机组次末级叶片断裂原因进行了失效分析,认为裂纹起源于表面的机械损伤,经疲劳扩展后最终导致断裂.     

U型螺栓失效断裂原因分析

某汽轮机组在运行过程中空冷岛风叶U型螺栓发生断裂,利用宏观形貌观察、化学成分检测、金相组织观察、断口微观形貌观察及力学性能测试等方法对 U型螺栓的断裂原因进行综合性失效分析。研究结果表明,由于螺栓的规格选用存在问题,导致 U型螺栓的弯曲半径小于风叶轮毂半径,从而使螺杆内弧侧与风叶轮毂的接触部位因长期磨损而形成应力集中,并诱发疲劳源。同时,U 型螺栓1的螺杆内弧与直杆过渡处存在一定程度的弯制残余应力,最终,在拉应力、弯制残余应力及风叶振动所产生的交变应力的综合作用下,疲劳裂纹源加速扩展,导致螺栓的断裂失效。     

200 MW汽轮机凝结水泵泵轴断裂失效分析

某200 MW汽轮机凝结泵泵轴在运行中发生断裂,对该轴断口进行宏观检测、金相检测、化学元素成分检测、力学性能检测和裂纹源区SEM扫描电镜及EDS能谱分析,其断口为典型的脆性断口,断裂方式为高周期疲劳断裂。该轴的热处理工艺与产品质量证明书要求不符,金相组织中存在的非金属夹杂物成为导致断裂的裂纹源,是发生疲劳断裂的主要原因。键槽位置设计不合理是发生断裂设计方面的原因。     

磨煤机电机主轴断裂原因分析

某电厂锅炉D磨煤机电机主轴在运行中发生断裂失效,通过宏观形貌分析、化学成分分析、显微组织检测、断口微区扫描电子显微镜分析、力学性能分析等方法,对主轴断裂进行原因分析。结果表明:其断裂的主要原因是电机主轴轴颈磨损后进行补焊修复的部位存在众多夹渣、裂纹及未熔合等焊接缺陷,主轴在长期重载运行频繁启动工况下首先在轴颈补焊修复部位的焊接缺陷处形成多源性疲劳裂纹源,这些裂纹源在周期性循环载荷作用下逐渐扩展并导致主轴最终疲劳断裂。     

On a wing and a prayer

The article talks about recent Defense Research Projects Agency (DARPA) presolicitation notice in the area of hybrid insect micro-electromechanical systems (MEMs). DARPA's goal is to fund promising interdisciplinary research that will permit the creation of "insect-cyborgs"     

Making a Case for a New Connector

The emergence of quick lock connectors, particularly quick lock versions of the SMA and N connectors (QMA and QN, respectively), was an inevitable development in the RF connector industry and is of significant importance in that nearly 50% of all practical applications for RF connectors are currently supported by either SMA or N. Once QMA and QN can achieve similarity in cost and performance to the present SMA and N connectors, they will take the place of their predecessors in most applications, creating a huge new market. Our RF team has long been dedicated to research and development of these two connector types in the hopes of creating an optimal design. In this article, we will show some of the results of our research.     

利用光伏电池给蓄电池充电

磷酸锂铁（LiFePO4）电池对比钻基德Li离子/聚合物电池,具有安全性性高、浮充电压小、自放电率低、使用寿命长等一系列优点。本文所述LT36521C为可实现太阳能跟踪、单块式补偿蓄电池充电的集成电路。当LT3652由单块太阳能电池板供电时,其输入调节回路能确保在最大输出功率下工作,充分体现出这一新型太阳能充电器的优越特性。     

Chaos in a series circuit with a nonlinear capacitor and a nonlinear inductor

This paper proposes a nonlinear circuit that generates chaotic oscillations. The proposed nonlinear circuit includes a nonlinear capacitor and a nonlinear inductor by using Generalized Impedance Converters. Both computational experiments and experiments on real circuits show that the region for chaotic oscillation is very wide, demonstrating that the proposed circuit is effective as a chaos generator. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(2): 35–42, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10361     

Electric potential near a tip of a local discharge on a conductive film

To develop a propagation model of a local discharge on a wet polluted insulator, the authors have examined characteristics of the local discharge on an electrolytic solution simulating the wet polluted insulator surface. The local discharge was propagated on the solution under the impulse voltage. A shape of a contacting surface between the local discharge and the solution has been already obtained by the authors. By using the contacting surface, an electric potential near a tip of the local discharge on a conductive film of 1 mm in thickness was calculated. Furthermore, the potential was measured with a probe. The calculated values and the measured values of the electric potential agreed well regardless of the propagation length of the local discharge, the width of the conductive film, the resistivity of the conductive film, the peak value of the applied voltage and the applied voltage waveform.     

Power losses in a conducting ring enclosing a conductor with a transient current

Contents In the paper Joule power losses are calculated in a conducting ring enclosing a conductor with a transient current having an alternating component.—Theoretical calculation and numerical computation are worked out basing on a link Bubnov-Galerkin method in its numerical version using the finite elements for the conductor with the Time-Stepping algorithm for the time discretization.—On the basis of numerical computation, graphs of the relative power losses are plotted as a time function.

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Leistungsverluste in einem leitenden Ring, der einen Leiter mit einem instationären Strom umschließt

Übersicht In diesem Beitrag werden die Joulschen Leistungsverluste in einem leitenden Ring berechnet, der einen Leiter umschließt, in dem ein instationärer Strom mit Wechselanteil fließt. Die theoretischen Betrachtungen und numerischen Berechnungen hat man in Anlehnung an die Bubnov-Galerkin-Methode (in ihrer numerischen Variante, die von einen Leiter unter Verwendung der Methode der finiten Elemente realisiert wird) in Verbindung mit einem Schritt-Algorithmus mit der diskretisierten Zeit ausgeführt. Auf der Grundlage numerischer Berechnungen sind Diagramme für die relative Leistung in Abhängigkeit von der Zeit dargestellt.

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List of symbols Symbol Unit Physical parameter - B Wb/m² magnetic induction vector - H A/m magnetic field intensity vector - H, H A/m -component of the magnetic field vector - E V/m electrical field vector - E _r ,E _z V/m components of the electric field - f s^–1 frequency - I A current intensity (r.m.s. value) - L H inductance - P W power losses - P ₀ W power losses for d.c. - R resistance - t sec time - ^–1 m_–1 electric conductivity of the conductor - Hm^–1 magnetic permeability - _ijk m² finite element area - basis function - rad s^–1 pulsation - N _i ,N _j ,N _k function of finite element shape - 3.141593... - region - ² Laplace's operator - r, ,z cylindrical coordinates - ^h region approximating the region - ^e finite element region - M number of discretization points of the region - V number of finite elements - (N–1) number of steps - i, j, k indices of vertices of triangular finite element     

Development of a deceleration control system for a winding machine based on a microcontroller

The development of an automatic deceleration system for a winding machine in a siderurgy factory is presented in this paper. The proposed system controls the speed of a winding machine in order to obtain the optimum stop point in terms of security and fast production. The system is based on a microcontroller and an extremely simple hardware. The system has been tested for two years and results evince a very good mean time between failures.     

When a feature detector becomes a feature generator

The neural network approach is reviewed in the context of studies in the animal and human visual systems. An attempt is made to explain perception, memory, and learning as a feedback loop similar to the one used in the ALOPEX optimization concept. Applications in pattern recognition and image processing are discussed. Experiments using visual evoked potentials in humans are described.     

Extension of a driving-point and a transfer function to a positive real two-port matrix

A solution is presented to the problem, which arises in two-port modelling, of determining a second driving-point function from a given driving-point function and a transfer function. the given functions must have a common denominator and satisfy the necessary positive real (PR) matrix conditions: the driving-point function must be PR and on the imaginary axis the real part of the transfer function must be zero whenever the real part of the driving-point function is zero. By using a partial fraction expansion and determining a required first-order polynomial, a unique second (minimum) driving-point function is obtained. Examples to illustrate the method are worked out.