Electromechanical Failure Research Articles

Fabrication and microstructure investigation of ultra-high-strength porcelain insulator

Abstract Insulators are essential components of power transmission network. With natural minerals such as bauxite and clay, we have fabricated ultra-high-strength porcelain insulator (UHSPI) of electromechanical failure load 420 kN determined by International Electrotechnical Commission (IEC), and have put it into production. Compared with other UHSPI fabricating methods, in which industrial alumina is used, our method is cost saving and rich in resources. The main objective of the study is to elucidate the relationship between microstructure (e.g. size, amounts and distribution of particles) and mechanical property of the sintered UHSPI and thereby to explore a way to further improve the mechanical property of UHSPI. The investigations of SEM, EDAX and XRD reveal that the strengthening mechanisms may be the combination of matrix reinforcement, mullite reinforcement and dispersion strengthening; high porosity (9.9%) and abnormal pores are more possible to be the main factor hindering electromechanical property improvement.

Electromechanical response and failure behaviour of aerogel-spun carbon nanotube fibres under tensile loading

The effect of tensile loading on the mechanical and electrical behaviour of carbon nanotube fibres spun continuously from an aerogel is discussed. While these fibres exhibit moderate strength (0.19 GPa) and elastic moduli (9.16 GPa), their piezoresistive behaviour, evaluated through active resistance measurements during tensile loading, demonstrates their potential for sensing applications in advanced composite materials. Insight into the failure behaviour of the aerogel-spun fibres is gained through microscopic examination of the failed fibres, as well as analysis of their electrical response. A new phenomenon for carbon nanotube fibres is reported—the aerogel-spun fibres are observed to undergo mild to severe kinking due to tensile failure. This kinking is attributed to compressive failure due to recoil from the fibre free ends. A simple analysis of experimental results yields a fibre compressive strength range of 172–177 MPa.

Degradation and Failure of Field Emitting Carbon Nanotube Arrays

It has been observed experimentally that the collective field emission from an array of Carbon Nanotubes (CNTs) exhibits fluctuation and degradation, and produces thermal spikes, resulting in electro-mechanical fatigue and failure of CNTs. Based on a new coupled multiphysics model incorporating the electron-phonon transport and thermo-electrically activated breakdown, a novel method for estimating accurately the lifetime of CNT arrays has been developed in this paper. The main results are discussed for CNT arrays during the field emission process. It is shown that the time-to-failure of CNT arrays increases with the decrease in the angle of tip orientation. This observation has important ramifications for such areas as biomedical X-ray devices using patterned films of CNTs.

Fault Diagnosis in Induction Motors Using the Hilbert-Huang Transform

The work carried out by the authors consists of applying a modern time-frequency decomposition (TFD) tool, the Hilbert-Huang Transform (HHT), to the diagnosis and the evaluation of electromechanical faults in induction machines. These machines are widely spread nowadays, being involved in many industrial processes as well as in power generation installations such as nuclear plants. The core of the proposed methodology is the analysis of the current demanded by the stator winding of the machine during its connection process known as startup transient. Once the current is analyzed, characteristic patterns caused by the evolution of certain components created by the corresponding faults are identified; this evolution is due to the dependence of these fault-related components on the slip s, a quantity varying during a direct startup transient from 1 to near 0. In the present paper, the HHT is applied to the diagnosis of two different faults: rotor bar breakages and mixed eccentricities. In comparison with other TFD tools, the HHT provides certain advantages that are discussed in the work. The validity of the approach is proven through several experimental tests on real machines with different sizes and characteristics. The results show the potential of the methodology for reliable fault diagnosis and for correct discrimination between the different electromechanical failures.

Innovative Design to Prevent Reversal of Roller Blood Pump Rotation in the Event of Electromechanical Failure: An Easy Solution to a Devastating Problem

Despite the advanced technologies of battery back-up for heart-lung consoles and the availability of system-wide generators, electromechanical failure is still occurring. Several heartlung machine manufacturers still provide unsafe handcranking devices to use in the case of an emergency while using a roller blood pump. A new design has been engineered to eliminate safety and quality issues for the perfusionist and the patient when the need for handcranking presents itself. A ratchet-style handcranking device was fabricated by means of a steel plate with adjustable pins. The adjustable pins allow for use with different models of the Cobe, Stockert, and Jostra heart-lung consoles, which contain roller pumps with 180° roller heads. Additional modifications such as a 1:2 transmission and fluorescent markers are also used in the design. This innovative design is an improvement in safety compared with the current handcrank provided by Cobe, Stockert, and Jostra. With this modified handcranking device, accidental reverse rotation of the roller pump head cannot occur. Fluorescent markers will improve visualization of the pump head in low-light situations. The ergonomic design improves efficiency by reducing fatigue. Most importantly, a “safe” safety device will replace the current design provided by these manufacturers, thus improving the quality of care by health care providers.

Statistical analysis of the electromechanical behavior of AgMg sheathed Bi2Sr2CaCu2O8+x superconducting tapes using Weibull distributions

Manufacturing of AgMg sheathed Bi2Sr2CaCu2O8+x superconducting tapes involves multiple processes. Microstructural studies across tape sections have shown that the microstructure is nonuniform across the tape. These nonuniformities are largely due to manufacturing defects, even in well-controlled manufacturing processes. Consequently, the electrical and mechanical properties vary in these different sections. Here, we report results from analyzing the electromechanical properties of AgMg sheathed Bi2Sr2CaCu2O8+x tapes in different sections using a statistical approach. 24 samples were studied at strains of 0%, 0.25%, and 0.349% for a total of 72 samples. The probability of electrical and mechanical failures of the tapes is then analyzed using two- and three-parameter Weibull distributions. It is found that the mechanical failure of these tapes is homogeneous, consistent with failure in the AgMg sheath, but that the electromechanical failure is inhomogeneous within the conductor and as a function of strain, indicating that this failure is dictated by failure in the inhomogeneous ceramic oxide superconducting filaments. This has important implications for the designs of superconducting magnets.

Self-assembly technique for MEMS vertical comb electrostatic actuator

We report a very simple and reliable method for making Self-Assembled Vertical Comb (SAVC) drive actuators by using the standard SOI bulk micro-machining processes. The initial angular offset of the movable combs is prepared by using the process stiction which occurs during drying process after sacrificial release. The optical scanner integrated with SAVC has shown good electrostatic scanning performance of over 1.0-degree static-rotation angle with a typical drive voltage of 20V without any in-use electromechanical failure.

Effect of an interphase layer on the electroelastic stresses within a three-phase elliptic inclusion

Electroelastic stresses induced by electromechanical loadings and lattice mismatch between components and surrounding materials are found to significantly influence the electronic performance of devices and, in some cases, are identified as a major cause of failure and degradation. To reduce electromechanical failure an effective method is to apply an intermediate layer, with appropriate geometry and material properties, between the components of dissimilar piezoelectric materials. In this paper, the effect of an intermediate layer on the electroelastic stresses within an elliptical inhomogeneity is examined within the framework of linear piezoelectricity. Exact closed-form solutions are obtained for the electroelastic stresses in the inclusion, the interphase layer and the matrix, respectively, under remote mechanical antiplane shear and inplane electric field, by means of the complex variable method. It is shown that the electroelastic stresses depend on only two complex coefficients. Simple formulae and numerical examples are used to illustrate the effects of the interphase layer on the electroelastic stresses within the inclusion, and the dependency of this effect on the aspect ratio of the elliptical inclusion.

American Heart Association Report on the Public Access Defibrillation Conference December 8-10, 1994

During the past 20 years, morbidity and mortality rates for nearly all types of cardiovascular disease have declined. Progress in these areas is in stark contrast to that for sudden cardiac death, which continues unabated at a rate of approximately 1000 times per day in the United States, with little decline in incidence or improved outcome. Clearly, the problem of sudden cardiac death is best approached through prevention, but horizons in that area seem no more promising and in some respects less promising and substantially more costly than 2 decades ago. The means necessary for successful resuscitation of a patient in cardiac arrest were known by the early 1960s. Externally performed cardiopulmonary resuscitation (CPR) could maintain an “oxygen plateau” and delay permanent brain damage long enough to allow external defibrillation using direct current (DC). The possibility of long-term survival was increasingly recognized, as early anecdotal experiences accumulated into published series.1 2 3 Given the hindsight of 3 decades, the obstacles to be overcome before significant progress could be made in out-of-hospital resuscitation were formidable. First, cardiac arrest was perceived as an event that typically occurred in the hospital. In-hospital cardiac arrests are now recognized to represent only a small proportion of sudden deaths based in the community. Second, the CPR technique was known to only a limited number of hospital-based physicians. CPR is no longer restricted to hospitals or physicians; it is routinely taught to the lay public. Third, only line-powered, bulky, and awkward defibrillators were available. The first out-of-hospital defibrillation device weighed 110 lb. Contemporary external defibrillators are available that weigh less than 10 lb. The present report details progress made in achieving the goal of facilitating out-of-hospital resuscitation and specifies those areas in which further headway is needed. This effort began in 1990 with an American Heart …

Internal Precipitation of Molecular Oxygen and Electromechanical Failure of Zirconia Solid Electrolytes

The phenomenon of electromechanical failure of zirconia has been examined. It is shown that spatial variation of electronic conductivity in a predominantly oxygen ion conductor can lead to internal precipitation of molecular oxygen and its pressurization. Internal pressures high enough to crack zirconia can develop if the electronic conductivity is higher on the oxygen exit side. The calculations demonstrate that the kinetics of pressurization are very sensitive to the relative magnitudes of the electronic and the ionic conductivities. Oxygen was electrolyzed at 800°C through zirconia solid electrolytes with lanthanum strontium manganate (LSM) electrodes under an applied dc potential of 1.0 V. Spalling of the solid electrolytes was observed. Composite disk electrolytes were fabricated such that part of the disk contained TiO2 as a dopant which was added to enhance the electronic conductivity. The electrolytes exhibited severe cracking and pitting when the TiO2‐doped region was on the oxygen exit side. No degradation occurred when the TiO2‐doped region was on the oxygen entry side. Implications regarding the use of mixed conductors as dense electrodes in electrochemical systems are discussed.

A Replacement Model for Multi-Tool Transfer Lines

Transfer lines have long been used for machining a single product at high production rates. This study deals with the transfer line, in particular, estimating the production time per part and the effect of using probability models in describing tool and machine lives. The production time is estimated using three major causes of line stoppage. An aspiration level criterion is used to establish a scheduled tool replacement interval. The aspiration decision parameter is system reliability. It is shown how a scheduled tool replacement interval could be established to obtain this reliability level. A methodology for selecting the replacement interval for a group of tools is developed and the impact of changing this interval on tool changing costs and tool failure costs is discussed. In this study, only a single premature tool failure is assumed to occur; however, the results are compared with multiple tool failures using the renewal function. It is shown that this single premature failure analysis is equivalent to the renewal function approach for machining systems having a reliability greater than 50 percent and tool failure variabilities having a coefficient of variation less than 1.0. Using the model developed in this paper, an example problem is presented. For this problem, electromechanical equipment failure and tool wear failures are modeled using the exponential and the Weibull probability distributions, respectively. Scheduled tool replacement intervals are developed for a range of target reliabilities. The part cycle time and operating cost for the transfer line based on these reliabilities are computed. These results are compared to the minimum cost reliability level. The minimum cost operating condition is dependent on the ratio of the scheduled replacement costs over the failure replacement costs. For the example presented, the reliability level at minimum cost is much lower than the desired target value of .9. This result illustrates the importance of conducting a careful analysis and using the results to help guide operating practices toward more efficient tool change practices and maintenance policies.

Effect of Chronic β-Blockade on the Ischaemic Myocardium

The long-term effects of chronic beta-blockade in the rat myocardium were investigated in terms of responses to ischaemic stress. Clinically relevant and equipotent doses of oxprenolol, propranolol, metoprolol, atenolol, and practolol were administered orally for 12 weeks. Twenty-four hours after the last dose, at a time when plasma drug levels were undetectable, hearts were excised and perfused as isolated preparations. During a 3-h period of low-flow, global ischaemia, the time to electromechanical failure following the onset of ischaemia was significantly increased in hearts from animals treated with drugs possessing intrinsic sympathomimetic activity (ISA). Similarly, with ischaemia-induced lactate and enzyme release, hearts from groups treated with drugs possessing ISA showed an increase in release above that of controls, or of hearts from rats treated with beta-blockers which did not possess ISA. These results suggest that in the isolated, globally ischaemic heart, when exogenous catecholamine drive is absent, long-term beta-blockade cannot exert a protective effect when circulating drug levels are undetectable, and compounds possessing ISA may increase tissue damage as measured by lactate and enzyme leakage.

Pacemaker therapy in children with complete heart block.

Permanent pacemaker therapy in children with complete heart block is necessary occasionally. Ten patients ranging in age from 8 months to 15 years were treated with an implanted P-wave, synchronous epicardial pacemaker. Indications for implantation were persisting postsurgical heart block, congestive failure, syncopal attacks, and arrhythmias. There were two deaths not attributed to pacemaker malfunction. The remaining eight children have been followed up for 38 to 108 months. There have been 27 pulse generator replacements. Twenty-three were for battery exhaustion, three for electromechanical failure, and one was due to arrhythmia. Rhythm disturbances have occurred on eight occasions. There have been no infections. It is concluded that the implanted P-wave synchronous pacemaker is an effective method of therapy when indicated for children with complete heart block.

Computer analysis of conditioned behavior

A computer program is described which is capable of summarising large amounts of data relating to classical and instrumental conditioning procedures. In addition to the normal probability and latency statistics simple anticipatory response sequences are quantified. A variety of fault finding procedures have been built into the program to protect it against electromechanical failures inherent in most behavioral apparatus.