Rotor fault condition monitoring techniques for squirrel-cage induction machine—A review

Nowadays, manufacturing companies are making great efforts to implement an effective machinery maintenance program, which provides incipient fault detection. The machine problem and its irregularity can be detected at an early stage by employing a suitable condition monitoring accompanied with powerful signal processing technique. Among various defects occurred in machines, rotor faults are of significant importance as they cause secondary failures that lead to a serious motor malfunction. Diagnosis of rotor failures has long been an important but complicated task in the area of motor faults detection. This paper intends to review and summarize the recent researches and developments performed in condition monitoring of the induction machine with the purpose of rotor faults detection. The aim of this article is to provide a broad outlook on rotor fault monitoring techniques for the researchers and engineers.     

Improving corrosion resistance of Al‐11mass%Si alloy through a large number of ECAP passes

Ultrafine‐grained (UFG) Al‐11mass%Si alloy, processed by multi‐pass equal‐channel angular pressing (ECAP) at 573 K, was investigated on corrosion behavior in 0.6 M NaCl solution. Potentiodynamic polarization tests and scanning electron microscopy observation showed that a large number of ECAP passes resulted in lower corrosion current density, more positive corrosion potential, and rather smooth corroded surface with shallow corrosion pits. The uniform distribution of fine secondary‐phase particles on UFG Al matrix weakened the susceptibility to pitting corrosion while inhibited general microgalvanic reactions. The present results indicate that grain refinement of aluminum matrix to the UFG state and uniform redistribution of broken particles (including eutectic silicon and secondary phases), via severe plastic deformation at elevated temperature undergoing dynamic recrystallization, can significantly improve the corrosion resistance of Al alloys, besides the known exceptional mechanical advantages. The simple and effective ECAP procedure makes UFG Al alloys more attractive for high strength structural application in corrosive environment.     

楔形头部试样的ECAP变形行为有限元模拟

应用三维有限元方法对楔形头部试样在等径弯曲通道挤压(ECAP)中的变形行为进行了模拟分析,以比较不同楔形方案(前楔形、后楔形以及楔形头部大小)对金属ECAP变形的影响.结果表明:试样头部为后楔形可以有效的降低加工载荷,显著改善应力/应变分布的均匀性,消除应变集中,避免折叠缺陷,从而获得组织性能较为均匀的试样.     

A modification on ECAP process by incorporating torsional deformation

In the present study, integration of equal channel angular pressing (ECAP), as a well known severe plastic deformation (SPD) technique, and torsion deformation, is studied by using three dimensional finite element analysis. This process is to be named as torsional-equal channel angular pressing (T-ECAP). In this modification a part of the exit channel in the ECAP die is rotating around its axis, to impose extra shear strains to the samples. To study deformation behavior in the T-ECAP process, three-dimensional finite element analysis (FEA) was carried out by using the elasto-plastic finite element analysis ABAQUS/Explicit Simulation. To investigate the validity of the simulation results, experimental studies were furthermore performed on commercially pure aluminum (AA 1050). Vickers hardness test was used to determine the distribution of hardness on both normal and longitudinal sections of the deformed samples with respect to the exit channel of the die. The hardness test results showed more uniform distribution of hardness in both sections of the T-ECAP processed samples regarding the ones produced by ECAP process. The load requirement comparison for performing both processes showed lower value for the T-ECAP with respect to the ECAP process. The simulation results for the strain values showed higher magnitude and more uniform distribution for the T-ECAP with respect to the ECAP process.     

Microstructure control during severe plastic deformation of Al-Cu-Li and the influence on strength and ductility

The microstructure and mechanical behaviour of an Al-Cu-Li alloy has been examined after processing over a wide range of conditions involving severe deformation at elevated temperatures with prior or subsequent heat treatments. Dislocation cellular or subgrain structures are obtained, with varying degrees of precipitation. High strength, as well as poor ductility, can be correlated with the presence of a high density of fine T₁ phase precipitates, with the dislocation substructure playing a smaller role. Careful control of processing conditions allows a suitable combination of good strength with ductility to be obtained.     

步进电动机的失调角及精度

步进电动机象同步电动机一样,在负载转矩的作用下,转子磁极中心线将滞后于气隙磁场的中心线一个角度,称为失调角。在开环控制系统中,负载失调角对应于一定的失动量。用脉冲当量来衡量失动量的值时,它与电动机的通电方式,主要是逻辑通电状态数,即通常所说的运行拍数有关。由此明确了微步驱动技术在开环控制系统中应用的局限性。     

原子辐射跃迁选择定则的一种半经典的推导方法

本文从对称性出发，用半经典的方法推导出原子辐射跃迁选择定则，指出该选择定则是角动量守恒定律在原子辐射过程中的一种表述。     

万向联轴节两轴角速比计算式的一个推导方法

本文从万向联轴节的速度分析入手，用初等数学的方法运用点的速度合成定理导出了该机构两轴角速比的计算式。与此同时，也明确地揭示出了该机构两轴瞬时转速不等的原因。     

对轴颈半速涡动的修正

对于无限长径向轴承，本文应用不可压缩流体连续性方程，求得轴颈涡动角速度，它小于转轴瞬时转动角速度之半。