Electron work function estimated from the delay time of breakdown in vacuum

The delay time of an interelectrode gap breakdown in vacuum was studied. A method for estimating the electron work function of a cathode with an extended working surface is proposed based on the breakdown delay measurements using applied voltage in the form of rectangular pulses or a sawtooth wave.     

Dynamics of the electrothermal instability of a polar dielectric in the temperature region of maximum relaxation losses

Under the action of an electric field, a polar dielectric may occur in several stable temperature states. Transitions between these states can be induced either by temperature perturbations or by changes in the load parameter depending on the frequency and strength of the electric field. A method is proposed for solving the nonlinear electrothermal problem of the temperature transition dynamics. The results of calculations of the temperature dynamics at the center of a dielectric are in good agreement with the data of numerical experiments.     

Determination of matrix dependences between the magnetic and elastoplastic characteristics of steels during tension

Stress-strain and coercive force-strain diagrams are experimentally obtained for grade 45 and St3 steels. These diagrams are used to construct matrix dependences between the elastoplastic and magnetic properties of the steels in order to determine the level of stresses in construction members made of these steels.     

Effects of blended vegetable‐based cutting fluids with extreme pressure on tool wear and force components in turning of Al 7075‐T6

In this study, performances of four different types of vegetable‐based cutting fluids (VBCFs) over a commercial mineral cutting fluid were evaluated for machinability of Al 7075‐T6. Lubrication properties of VBCFs were improved with additive of extreme pressure. Cutting force and tool wear data were obtained for performance analyses of cutting fluids during longitudinal turning of Al 7075‐T6. Cutting, feed and radial forces indicated 1.70–38.25% improvements for VBCFs over the commercial mineral cutting fluid. The lowest average values of flank and nose wears obtained with blended cutting fluid containing 12% of extreme pressure were 0.09 and 0.10 mm, respectively, whereas these values for the commercial mineral cutting fluid were 0.18 and 0.15 mm. The scanning electron microscope results showed adherence of workpiece material occurred on rake and flank faces, and flank and nose wears were the dominant wear modes. It was found that performances of VBCFs during turning of Al 7075‐T6 were better than that of the commercial mineral cutting fluid. Copyright © 2012 John Wiley & Sons, Ltd.     

Experimental investigations of vegetable based cutting fluids with extreme pressure during turning of AISI 304L

Experimental studies on the performances of both new developed environmental friendly vegetable based cutting fluids (refined sunflower and canola oils) including different percentage of extreme pressure (EP) additive and two commercial cutting fluids (semi-synthetic and mineral cutting fluids) in turning processes were reported in this work. Performances of cutting fluids were compared with respect to surface roughness, cutting and feed forces and tool wear during longitudinal turning of AISI 304L. Experimental results were also compared with dry cutting conditions. The results indicated that 8% of EP included canola based cutting fluid performed better than the rest.     

Influence of a Low-Temperature GaAs Dislocation Filter on the Perfection of GaAs/Si Layers

The influence of dislocation filters based on low-temperature layers (LT) of GaAs and postgrowth annealing on the perfection of GaAs/Si heterostructures is discussed. It is shown that LT-GaAs layers reduce the density of threading dislocations and surface roughness. Post-growth annealing at a temperature of 650 °C reduces the concentration of nonradiative recombination centers in GaAs/Si layers to a level close to the level in GaAs layers grown on a matched substrate.     

Experimental diagnostics of ball bearings using statistical and spectral methods

Vibration measurements and signal analysis is widely used for condition monitoring of ball bearings as their vibration signature reveals important information about the defect development within them. Time domain analysis of vibration signature such as peak-to-peak amplitude, root mean square, Crest factor and kurtosis indicates defects in ball bearings. However, these measures do not specify the position and/or nature of the defects. Each defect produces characteristic vibrations in ball bearings. Hence, examining the vibration spectrum may deliver information on the type of defects. In this paper a test rig is designed and a pair of brand new commercial ball bearings is installed. The bearings run throughout their lifespan under constant speed and loading conditions. Vibration signatures produced are recorded and statistical measures are calculated during the test. When anomalies are detected in the statistical measures, vibration spectra are obtained and examined to determine where the defect is on the running surfaces. At the end of the test, the ball bearings are disassembled in order to take microscopic photos of the defects.