Machinability of ZTA-TiC Ceramics by Electrical Discharge Drilling

AbstractElectric discharge machining of ceramics becomes principally feasible if the ceramic material has a sufficiently high electric conductivity. This can be achieved by adding transition metal carbides, borides or nitrides such as titanium carbide. In case of electric discharge drilling the small electrode dimensions lead to higher current densities compared to die sinking. In order to avoid bursting of the ceramics by thermal shock machining parameters have to be well adjusted and the material should have a high thermal conductivity. A parameter study was carried out to observe the removal behavior depending on machine parameters such as discharge energy, pulse form and flushing conditions

Mechanically assisted electrochemical degradation of alumina-TiC composites

Alumina-TiC composite material is a tough ceramic composite with excellent hardness, wear resistance and oxidation resistance in dry and high-temperature conditions. In aqueous conditions, however, it is likely to be electrochemically active facilitating charge transfer processes due to the conductive nature of TiC. For application as an orthopedic biomaterial, it is crucial to assess the electrochemical behavior of this composite, especially under a combined mechanical and electrochemical environment. In this study, we examined the mechanically assisted electrochemical performance of alumina-TiC composite in an aqueous environment. The spontaneous electrochemical response to brushing abrasion was measured. Changes in the magnitude of electrochemical current with abrasion test conditions and possible causal relationship to the alteration in surface morphology were examined. Results showed that the alumina matrix underwent abrasive wear with evidence of microploughing and grain boundary damage. Chemical analysis revealed TiO2 formation in the abraded region, indicating oxidation of the conductive TiC domain. Furthermore, wear debris from alumina abrasion appeared to affect reaction kinetics at the composite-electrolyte interface. From this work, we established that the composite undergoes abrasion assisted electrochemical degradation even in gentle abrasive conditions and the severity of degradation is related to temperature and conditions of test environment

Surface temperature measurement of a copper anode submitted to a non-stationary electric arc in air

This work concerns the assessment of the surface temperature of copper anodes submitted to an electric arc in a non-stationary regime in air at atmospheric pressure. An infrared camera is used to measure the decrease of the surface temperature just after a very fast controlled arc extinction. Results are presented for different mean values of the arc current intensity (30, 70 and 130 A) with an electric arc duration in the range of 2–5 ms. The temperature decrease after the arc extinction allows an assessment of the surface temperature just at the moment of the arc switching off. In the present experimental conditions the mean temperatures reached for copper anodes are in the range of 750–1200 °C according to the arc current intensity values. Comparison between experimental results and a numerical modeling of the electrode heating allowed one to assess the surface power balance. The values for the volt equivalent are found about 12 V and the values for the surface power density are found to be near 2 × 109 W/m2

Arcing fault in aircraft distribution network

International audienc

Comparison of the effect of different types of aging on partial discharge inception voltage in aerospace power connectors

International audienc

PROGRESS IN SATELLITE TRACKING CRANES

We review the history of tracking cranes with satellite telemetry and identify some of the difficulties in designing satellite transmitters and harnesses for cranes. Miniaturization of these transmitters and a plethora of harnessing experiments since 1989 allow us to recommend limited application of this technology to all species of cranes. We are still uncertain, however, if cranes harnessed with satellite telemetry devices are able to reproduce after migration. Because of this uncertainty, we urge caution in the use of this technology, especially with breeding adults in severely endangered popUlations. This manuscript also describes continuing research needs

Simple 1D model of a short gap DC electric arc in in aeronautical pressure conditions

International audienceIn the next few years the electrical power embedded in future aircrafts will strongly increase. The supply voltage will increase to 230 VAC and ± 270 VDC or 540 VDC; thereby studies concerning the embedded equipment behavior must be done. For such power networks characteristics the risk of arc fault and requirements for arc tracking will also increase. The aim of this work is to propose a simple 1D model of a DC short gap electric arc in aeronautical pressure conditions: i.e. a pressure in the range [10 mbar-1 bar] which corresponds to the aircrafts altitudes. By emitting certain assumptions, the approach is to find the temperature distribution in the arc column and deduce from that the characteristics of the arc current as a function of electric field in the column and the maximum temperature in the center of the arc column. The novelty of this work is the observation of the evolution of the temperature (and as a consequence the evolution of the arc current) if we assume that the radius of the arc column is not limited like in wall stabilized arc where the wall is water cooled, the arc radius can expand as much as possible. The study is done in the air

Physical properties of the swept arc channel in the context of lightning strikes to aircraft

International audienceDuring an in-flight lightning strike, the relative motion between the arc channel and the aircraft causes a sweeping of the attachment point on the aircraft skin. To predict the behaviour of the arc channel and therefore the potential locations for further restrikes, this study aims at investigating the phenomenon with an innovative method for producing sweeping arcs based on a stationary arc and an electromagnetic launcher propelling aeronautical samples. This article focuses on characterisation of the arc channel, aiming at establishing the evolution of its physical properties during swept-stroke for various experimental conditions. Firstly, the experimental coupling of the lightning generator with the electromagnetic launcher and with a wind tunnel is described with a discussion on the representativeness of the experiment. Then, high-speed cameras and voltage and current probes are used to measure the electrical and geometrical behaviour of the electric arc channel during a swept-stroke. The shape, the length, the voltage and the power evolution of the arc channel are evaluated for different input parameters such as speed, polarity, arc current and sample length. Furthermore, the influence of these parameters on the temperature of the arc channel is studied, resorting to an optical emission spectroscopy technique. The results are presented and discussed with the objective of providing a physical insight into arc elongation phenomenology during a swept-stroke

Parametric Study of the Current-Voltage Characteristics of a 100-mbar DC Discharge in Argon: From the Diffuse Glow Discharge to the Arc Regime

International audienceThe aim of this paper is to investigate the glow discharge in its diffuse and filamentary regime, and to study its transition to arc in argon at 100 mbar. The structure of the discharge is observed in correlation with its electrical signals in both static and in dynamic modes. Glow discharges were identified with a positive column that can be fully diffuse, fully filamentary, or a mix of the two with the filamentary part of the column always attached to the anode. Spontaneous transitions between glow discharges and arcs have also been observed and their dynamics are studied. Using high-speed imaging, the transition between glow and arc discharge was identified as the occurrence of two distinct phenomena: a propagation mechanism in the positive column and a constriction of the cathode root. An evaluation of the duration of each phenomenon as a function of electrode gap and current intensity was obtained. The duration of the constriction of the cathode root is found to be on the order of tens of nanoseconds and the duration of the propagation mechanism in the range 50-550 ns