低速重载轴承的故障诊断

分析了低速重载轴承的故障特点及其诊断方法,分别就内圈故障、外圈故障、滚动体故障、保持架故障的诊断方法以及故障的严重程度的判断进行了讨论,并用此方法对两例轴承故障实例进行了分析。     

数控机床故障维修实例与分析

数控机床故障一般有数控系统本身的硬件故障,主轴放大器和主轴伺服电机故障,进给伺服放大器和进给电机故障,机床PMC(I/O)故障,操作错误及编程错误故障,外界干扰引起的故障,现场机床电气部分故障,机床机械本体故障等。通过介绍数控加工中心实际生产使用中的几个相关故障现象,进行故障原因分析,给出了诊断过程以及解决问题的办法。     

汽轮发电机振动故障专家系统诊断方法研究

通过对汽轮发电机振动故障机理、故障特征和故障原因的分析,建立了汽轮发电机振动故障特征表,根据振动故障特征表的知识以决策树的形式构建了汽轮发电机振动故障专家系统知识库,并建立了汽轮发电机振动故障专家系统决策树诊断模型。最后通过发电机振动故障实际案例对汽轮发电机振动故障专家系统诊断方法进行了验证,证明了其准确性和可行性。     

浅析电气控制线路故障与维修方法

电气控制线路故障是工作中常见的电气故障之一,也是电气维修中最多的故障。如何在出现故障时,能迅速查明故障原因、正确处理故障,是保证设备正常运行的重要前提。本文针对电气控制线路故障的维修方法和程序进行叙述,以提高实际工作中故障排查的效率。     

电力系统利用小波奇异性的行波故障测距

高压输电线路故障的准确定位,能够缩短故障修复时间,提高供电可靠性,减少停电损失.对于占绝对多数的瞬时性故障来讲,准确的故障定位可以找出故障的原因,及时发现隐患,防止事故再次发生.基于小波变换的行波故障测距系统将小波变换引入双端行波故障定位,实现了快速可靠的定位和选相.     

板带轧机HAGC系统基于小波变换的传感器故障诊断

 提出了一种基于小波分析的HAGC系统传感器故障诊断方法。通过建立系统的MA模型，建立残差信号，利用离散小波变换对残差信号进行多分辨率分析。通过残差信号的故障高低频特性，提取故障敏感特征，实现了传感器故障时间、故障原因、故障程度的诊断。仿真研究表明，该方法凸现故障特征，时域定位准确，不但适用于突变故障，对渐变故障同样有效。     

数字传动系统调试与常见故障处理

数字传动系统是实现金属加工传动控制的电机系统,数字传动系统常见的故障主要有滚动轴承故障、旋转机械故障、齿轮故障和往复式机械振动故障等,采用数字传动系统输入输出信号分析和检测方法进行系统调试和故障分析,实现对传动系统的工况状态识别和故障检测,确定故障的原因和部位,达到故障诊断决策目的。数字传动系统的故障处理方法主要采用输入主分量分析方法、故障特征聚类分析方法和专家系统诊断识别方法。以某大型数字传动系统的滚动轴承故障为例,进行系统调试和故障检测设计和仿真分析,展示较好的故障诊断性能。     

浅淡电脑主板故障的分析和维修

主板故障种类分为局部性、全局性 ;稳定性、不稳定性及电源故障、总线故障、元件故障等。根据不同的故障分类进行检查处理 ,方法有清洁法、观察法、电阻、电压测量法等。     

沃尔沃铰接式卡车电气系统故障诊断

沃尔沃铰接式卡车电气系统采用国际通用的车载电子控制系统,当车辆自诊断系统诊断出故障,并给出故障代码以后,我们可以通过对传感器基本信号数据的关联分析和对应分析来初步确定故障部位,同时将故障代码提示的车辆故障现象与实际故障现象进行对比,从而快速得到正确合理的判断,而不是将故障代码作为解决问题、排除故障的唯一依据。     

三相异步电动机故障的分析、检查和判断

为了能在短时间内有效地排除电动机的故障,以利于及时恢复生产,电工必须学会分析、检查和判断电动机故障的方法.一、三相异步电动机常见故障的分析 分析电动机的故障,是从电动机故障的现象开始.但是,电动机的某几种故障往往有同样的表现,而一种故障也往往在几方面表现出来,此外电动机上表现出来的故障,有时故障并不在电动机本身,而是在电源起动设备等方面.因此,根据现象要判断电动机故障,一定要从多方面去分析.     

Analytical Approach to Calculate Rate of Bank Erosion

Bank erosion consists of two processes: basal erosion due to fluvial hydraulic force and bank failure under the influence of gravity. Because bank resistance force varies with the degree of saturation of bank material, the probability of bank failure is the probability of the driving force of bank failure being greater than the bank resistance force. The degree of saturation of bank material increases with river stage; therefore, the frequency of bank failure is correlated to the frequency of flooding. Consequently, the rate of bank erosion is due to both basal erosion and bank failure, and bank failure is a probabilistic phenomenon. In this paper, for cohesive bank material experiencing planar bank failure, a deterministic approach was adopted for basal erosion analysis, whereas the probability of bank failure was included in the analysis of bank failure. A method for calculating the rate of bank erosion was derived that integrates both basal erosion and bank failure processes, and accounts for the effects of hydraulic force, bank geometry, bank material properties, and probability of bank failure.     

Model Tests and Analyses of Bearing Capacity of Strip Footing on Stiff Ground with Voids

A series of 1G loading tests under the plane-strain condition were conducted on stiff ground with continuous square voids with the view of shallow foundation on calcareous sediment rocks, which contain voids because of their susceptibility to water dissolution. Detailed experimental observation revealed three types of failure modes for a single void: bearing failure without void failure, bearing failure with void failure, and void failure without bearing failure, depending on the location of the void as well as the size of the void. Upper-bound calculations were presented to interpret the changes of bearing capacity observed because of the existence of a void.     

宝钢RH真空系统稳定运行的研究与实践

在炼钢厂生产高附加值的品种钢必须通过RH精炼工序,而RH装置中的真空系统是否稳定是决定钢水质量的关键因素。介绍RH真空系统故障的分类,包括能源介质的故障、漏气故障及真空元件的故障。对每类故障的原因进行分析,并结合现场实际案例,快速确认故障原因。从真空度维护方面介绍了几种有助于真空系统稳定运行的措施,经实践证明非常有效,对同类真空系统的运行有一定借鉴意义。     

Analysis of Test Specimens for Cohesive Near-Bond Failure of Fiber-Reinforced Polymer-Plated Concrete

The failure mechanisms of reinforced concrete (RC) members change due to the application of externally bonded fiber-reinforced polymer reinforcement. Although an extensive literature is available describing the failure mechanisms of poststrengthened flexural systems, brittle failure modes caused by bond failure, such as midspan debonding and end peeling, need to be further investigated in order to identify and quantify the fracture processes that result in bond failure. Simplified experimental tests have been designed to idealize the bond between the laminate and the RC member. However, it is unclear how the simplified test results can be related to the actual flexural debonding failures. This paper investigates and compares two bond failure tests: a simplified test (or simple shear test) and a recently proposed shear/normal test. After discussing the characteristics of both tests and how they relate to the midspan debonding and end peeling failures, the shear/normal test is studied in more detail using a nonlinear finite-element fracture mechanics program. The program accounts for cohesive localized and distributed concrete crack damage and is capable of describing the geometrical discontinuities that induce different brittle failure mechanisms. The numerical results compare well with available experimental data and help explain the crack formation and propagation pattern up to specimen failure. Parametric studies are presented to elucidate the influence of different material parameters on the failure mechanisms.     

Tensile fracture of brittle matrix composites: Influence of fiber strength

A stress intensity approach is used to analyze tensile failure of brittle matrix composites that contain unidirectionally aligned fibers held in place by friction. In general, failure may initiate either by growth of a crack in the matrix, or by fracture of fibers that bridge the matrix crack. Subsequently, these failure processes may continue either unstably or stably with increasing applied stress. Solutions to the fracture mechanics analysis are obtained numerically in normalized form, with one microstructural variable, the normalized fiber strength. The analysis defines transitions between failure mechanisms and provides strength/crack-size relations for each mechanism. Explicit relations are derived for the matrix cracking stress (noncatastrophic failure mode), the condition for transition to a catastrophic failure mode, and the fracture toughness in a region of catastrophic failure, in terms of microstructural properties of the composite.     

Failure of resistance spot welds: tensile shear versus coach peel loading conditions

Abstract

This paper aims at investigating the failure behaviour of resistance spot welds under tensile shear (TS) and coach peel (CP) loading conditions. A failure mechanism was proposed to describe both interfacial and pullout failure modes in each loading condition. The mechanisms were confirmed by SEM investigations, examining the cross-sections of the fractured welds to detail the fracture path. The experimental results showed that in the pullout failure mode during TS testing, necking is initiated at the nugget circumference in the base metal, and then failure propagates along the nugget circumference in the sheet, leading to the final fracture, while pullout failure during the CP test occurred by crack initiation and propagation near the weld nugget/heat affected zone boundary. The interfacial failure to pullout failure mode transition in the TS and CP tests was also studied. The critical weld nugget size required to ensure the pullout failure mode was obtained for each loading condition. The critical fusion zone size to ensure pullout failure mode during the TS test was larger than that of the CP test. It was found that the load bearing capacity of the spot welds under CP is significantly lower than that of the TS test.     

缺口对渗氮CrNiW钢超高周疲劳特性的影响

 为了研究缺口敏感性对渗氮CrNiW钢疲劳特性的影响,设计了一种光滑试样和两种缺口试样(应力集中系数K_t=1.20、1.55),开展了渗氮CrNiW钢的超高周疲劳试验,使用SEM观测疲劳断口的微观结构,分析了疲劳缺口系数K_f、疲劳敏感系数q和循环周次N_f之间的关系。结果表明,渗氮对钢材疲劳性能的提升不大,光滑试样和K_t=1.20的缺口试样存在表面和内部两种起裂模式,诱发内部起裂的缺陷均位于内部非渗氮区,K_t=1.55时发现一种新的渗氮层内不均匀基体组织诱发的失效模式。光滑试样未出现双重S-N特性,K_t=1.20时S-N曲线出现表面与内部起裂双重S-N特性,K_t=1.55时出现短寿命区和超高周寿命区表面起裂双重S-N特性。随着K_t的增大,多个内部缺陷同时萌生裂纹的现象被单裂纹源诱发失效的现象取代,并且诱发失效的内部缺陷位置呈现向试样表面靠近的趋势,鱼眼形状呈近似横向扁形→圆形→纵向椭圆形变化。缺口应力集中对表面起裂疲劳寿命影响较大,对内部起裂疲劳寿命影响很小。     

Physiopathological basis of the treatment of heart failure

Therapeutic advances have changed the mode of presentation of cardiac failure over the last decades: the main cause, nowadays, is myocardial ischaemia. The modern treatment of cardiac failure is based on relatively simple physiopathological mechanisms which take into account the different aspects of cardiac physiology: a pump, a muscle, a coronary circulation supplying oxygen to the myocardium, an automatic contraction. The concept of vasodilatation and the blocking of vasoconstrictive systems introduced during the 70s is the basis of modern treatment of cardiac failure which involves angiotensin converting enzyme inhibitors and, increasingly, betablockers. In the near future, with earlier treatment of cardiac failure, the stimulation of vasodilator systems could become a new therapeutic strategy. Early detection of ischaemia and its complications with the aim of limiting the loss of cardiac myocytes is a priority for slowing the progression of cardiac failure. The prevention of cardiac failure also depends on educating cardiologists to treat rapidly the factors predisposing to or prolonging episodes of even mild cardiac failure.