Microwave Absorption Studies on Superparamagnetic Conducting Nanocomposites as Signal Coating Materials

In this paper, preparation and characterization of superparamagnetic nanoparticles and their polymer composites prepared by varing doping level of conducting polymer and their microwave absorption studies at radar system in 8–12 GHz frequency range have been discussed. These composites are conducting polymers have been widely used because of their lower density as well their good environmental stability as in the case of polyaniline (PAN). In the present work, in situ polymerization of aniline was carried out in the presence of 30 mole% Fe₃O₄ nanoparticles to synthesize polyaniline/Fe₃O₄(PAN/Fe₃O₄) composites in epoxy resin matrix. The composites, thus synthesized have been characterized by infrared (IR) spectroscopy and X-ray diffraction. The morphology of these composites was studied by scanning electron microscopy. The measurement of % absorption was carried out in X and K band microwave region.     

Iron and copper complexes with nitrogen-containing ligands as catalysts for cyclohexane oxidation with hydrogen peroxide under mild reaction conditions

Oxidation of cyclohexane (CH) with hydrogen peroxide under mild reaction conditions in the presence of systems containing in situ generated iron complexes with nitrogen-containing ligands (2,2??-bipyridyl and o-phenanthroline) and chlorinated (Cl15) copper phthalocyanine (CuPcCl₁₅) have been studied. It has been shown that in water-acetonitrile blends under optimum conditions, CH is oxidized with the formation of cyclohexanol, cyclohexanone, and acids involving cyclohexane hydroperoxide. High total selectivity for ketone and alcohol is reached in the excess of ligands and the substrate.     

Acoustic-Emission Testing of Failure in Samples of CFRP Exposed to Static and Heat Loads

The results of testing samples made of T700 carbon fiber reinforced plastic with a stress concentrator in the form of a hole 14 mm in diameter are considered. Some of the samples were heated to a temperature of +100°C, followed by exposure to a static tensile load, with the remaining samples statically loaded at a temperature of +20°C. In the process of loading, information was recorded using the method of acoustic emission. At first, the samples were loaded statically up to 50 kN, which was 50% of the average breaking load. Then the load was increased in increments ΔP = 10 kN until sample failure. It was observed that the simultaneous exposure of samples to static and heat loads decreased the load capacity of the samples.

     

Estimation of time-of-arrival errors of acoustic-emission signals by the threshold method

A technique for determining the times of arrival of acoustic-emission (AE) signals at the probes of a piezoelectric antenna with simultaneous estimation of their errors is considered. To increase the localization accuracy, it is proposed to refine the times of arrival by linearly approximating the leading edge of an AE signal taking into account the influence of noise. The slope of the leading edge is calculated according to the criterion of the minimum rms deviation from the signal envelope using the moving-window method. Examples of use of the developed method for calculating the coordinates of flaws in strength tests of structural elements are considered.     

Development of the technique of clustering by acoustic emission signal parameters

The technique of clustering by a set of parameters of acoustic emission (AE) signals, which allows reducing the time of processing of the recorded data, is considered. A comparative analysis of the stability of three clustering techniques (by shape, leading edge rise rate, and a set of AE signal parameters) with respect to the effect of random noise distributed according to a normal law is performed. A possibility of using the considered clustering techniques for distinguishing different stages of duralumin specimen fractures and during welding of steel specimens is experimentally demonstrated.     

Dynamics of the formation of pulsed transverse nanosecond discharge with prolate slot-cathode

Experimental studies of the spatial-time dynamics in formation and evolution of nanosecond plasma-beam discharge with a prolate slot-cathode in inert gases is investigated using a high-speed camera. Features and regularities in the dynamics of evolution of nanosecond discharge with the slot-cathode are established depending on the external conditions. As it has been shown experimentally, the first registered optical radiation of the discharge arises near cathode surface and the discharge formation starts simultaneously at the cathode slit output and between the electrodes.     

Intensifying removal of particulate contaminant from hydrocarbon feedstock with a magnetic field

The effect of a constant magnetic field on hydrocarbon feedstock of different natures was investigated. The effect of magnetic induction on the size of disperse particles was established. The effectiveness of the magnetic field on treatment of hydrocarbon feedstock to remove particulate contaminants was demonstrated.     

Study of fracture of specimens made of fiberglass plastic using acoustic-emission and strain measurements

The crack resistance of specimens made of a fiberglass plastic composite material has been studied. All specimens had approximately the same geometric dimensions. At the center of the specimens, there were 25-mm-long notches on both sides. The specimens were loaded with a static or cyclic load at a frequency f = 5 Hz. The tests were performed using acoustic-emission (AE) and strain gage measurements. The AE technique allowed stable localization of a flaw at an early stage of growth and made it possible to automate the measurement process. The strain gage measuring system was used to find deformations in the zones of localization of AE signals.