Materials Science Forum Vol. 970

Abstract: A surface charge density distribution on natural crystal samples is investigated in the paper. Here are revealed regularities of electromagnetic signal amplitude changes upon acoustic excitation of electrified calcite samples depending on the size of the crystals.

Abstract: Neutron degradation of LEDs based upon AlGaInP heterostructures (λ=630 nm and λ=590 nm) with multiple quantum wells are presented in the article. For the initial red LED (λ=630 nm) we can clearly distinguish three characteristic regions. In the small current region a low electron injection mode into the active region of the LEDs is observed. Further, as the operating current goes up, there are average and high electron injection in the active LEDs area regions. However, for the LEDY, the difference in the average and high electron injection regions is more pronounced and low electron injection region is absent. The boundary between the average and high electron injection regions can be characterized by the boundary current, which goes up with increasing exposure level. Three regions of electron injection in the active area of LEDs: low, average and high electron injection are illustrated for both types of LEDs under fast neutron irradiation. Based on the established relationships describing the emission power changing, a phenomenological model of the radiation hardness of LEDs based on AlGaInP heterostructures with MQW was shown. The LEDs radiation hardness is determined by the boundary current value, emission power in the low electron injection into the active LEDs area, the initial defective structure.

Abstract: The most common reason of the fatigue crack appearance is the presence of stresses in the rail. The process of stress strain state simulation for the R65 rail is presented in the paper. Values of residual stresses were modeled and chosen to be maximum allowed by GOST (State Standard): -77 MPa in the rail head, -125 MPa in the web and 106 MPa in rail foot. These stresses match the value-77 MPa measured by the acoustoelastic method from the center of the rolling surface of the rail. The influence of the crack at the highest level of the stress strain state was studied in cases of the maximum train load and its absence. According to results of modeling, stresses in the sharp edge of the crack can exceed the lowest acceptable by GOST (State Standard) value of the yield strength by more than 5 times in case of the presence of the train load. In case of the absence of the train load, the crack does not have a significant influence on the stress strain state. The modelling process was also used to study the influence of the installation temperature difference on the operational lifetime of the rail. The paper presents the description of the influence between the installation temperature difference and the crack initiation. According to modeling results and the rail defect catalogue, rails with the lowest acceptable mechanical characteristics are prohibited to be used after 300∙10⁹ kg and higher tonnage.

Abstract: A mathematical model has been developed to simulate the initial projections for computed tomography of large-sized oil and gas pipes and to transform the projections into the mass thickness distributions. The simulated projections of steel pipes with a diameter from 530 mm to 1420 mm are given with variation of ADC capacity and the number of photons incident on the front surface of the multichannel bremsstrahlung detector. The necessity of correct selection of these parameters is proved. A possibility to estimate the density distribution over a pipe cross section based on the inverse Abel transform for the fan-beam of bremsstrahlung is illustrated. The issues related to the technical feasibility of the computed tomography method for inspecting of large-sized pipes and concerning the estimation of the total scan time and the choice of ADC capacity are considered. Recommendations on the adjustment of the analog and digital signals ranges are given. The obtained results make it possible to evaluate the feasibility of designing a computer tomography system for monitoring large-sized oil and gas pipes.

Abstract: The article proposes the use of the acoustic waveguide method with normal Pochhammer waves to estimate the water absorption of composite fiberglass rebars. The results of experimental studies on the water absorption and temperature influence on the propagation velocity of rod and torsional waves in composite rebars samples with different physical and mechanical characteristics are presented. The sensitivity of the wave velocity parameter to water absorption and temperature fluctuations is estimated. The proposed acoustic waveguide method is characterized by high accuracy, reliability and efficiency.

Abstract: The mathematical model of the broadband transmission X-ray thickness gauge is developed. The mathematical model consists of sectors: generation and transformation of radiometric signals; equation of transmission X-ray thickness gauge; error estimation of thickness measurement; performance rating. The example of the use of the proposed model to calculate of the transmission X-ray thickness gauge for aluminum items is provided. In the example the dependences of integral mass X-ray attenuation coefficients and the thickness of monitored objects made from aluminum are calculated. The range of optimum measured thickness depending on the maximum X-ray energy was selected, the measurement time to provide the desired thickness measurement error was estimated. The possibility of measuring the thickness of a cooper test object for a wide beam conditions has been experimentally confirmed.

Abstract: A new colorimetric optode has been developed for preconcentration and visual determination of mercury ions in fish products. This optode is based on the color reaction of copper diethyldithiocarbamate with Hg²⁺ in the body of polymethylmethacrylate matrix. The optode exhibited sensitivity through the change of color from brown to colorless, which could be easily detected by naked-eye or spectrophotometric method. The influence of acidity, contact time and interference of foreign metal ions has been studied. The optode revealed good linearity in the range of 20-360 μg·L^-1, with a limit of detection of 8 μg·L^-1 Hg²⁺ at pH 5.2 and response time of 10 min.

Abstract: Effect of electrode degradation on stability of nugget formation during small-scale resistance spot welding is presented in this paper. Production of spacer grids for nuclear fuel assemblies made of E110 zirconium alloy cells of 0.25 mm thickness was studied. The following degradation processes took place in the electrodes as they wore. Roughness of the tip surface was gradually reduced to the values of the welded cells. The semispherical tips were severely deformed during the initial period of their operation (1.500...2.000 welds). The deformation dynamics slowed down significantly after that. Microhardness on the tip surface of the electrodes decreased. It was minimal in the central part of the surface layer with a thickness of 50...100 μm and increased towards the periphery. Significant coarsening of the electrode metal microstructure occurred at a depth of ~ 1 mm. Nugget area and its tensile strength decreased as the electrodes wore. An increase in welding current did not reduce deterioration of nugget quality. Measurement and processing of dynamic resistance between electrodes did not make it impossible to predict and control the properties of nuggets for the studied welding modes.

Abstract: This article presents the results of a study of the effect of crack formation in concrete that occurs during uniaxial compression on the parameters of the electrical response under periodic impulse shock action. Researches were conducted on fibre-reinforced concrete samples and samples without reinforcement. It is shown that the method based on mechanoelectric transformations phenomenon can be equally applied to both unreinforced and fibre-reinforced concrete samples.

Abstract: Within this article, a method has been developed to reduce the amount of transmitted data from the receiving and preprocessing unit to a personal computer. On logical grounds, there is compelling reason to use as a basic property of an ellipse as a ground of the method. The developed data processing algorithm for the multi-element array system was tested in the MatLab software package. Also, a block diagram and data processing algorithm were developed for the practical implementation on a field programmable gate array.