Papers by Keyword: Heterogeneity

Abstract: The drying process that is responsible for ensuring the coffee quality, reduces the moisture of the coffee bean thus avoiding unwanted microorganisms. Traditional drying methods take between 16 and 45 hours to dry coffee beans, which results in high operational costs. Therefore, the application of the microwave drying technique is a possible alternative, as it can reduce drying periods by four times. In this study, the main goal was to evaluate the heating kinetics and distribution of a single coffee bean due to microwaves to verify its heterogeneity. Initially, a single coffee bean was designed and inserted into a monomode microwave cavity. The geometry of the coffee bean was simplified as a semi-ellipsoid with its diameters measured experimentally and with four different curvatures at the edges. As a result of the numerical simulations, the temperature distribution on the coffee bean over time was obtained as well as the average temperature and temperature at its center. The heating kinetics plot described a linear curve for every geometry, having a higher inclination in the sharp edge and decreasing as the curvature increases. Also, when comparing the average and center temperatures, the temperature in the center is 107.58 °C and the average temperature of the coffee bean is 96.09 °C, which corroborates the fact that the microwave heating occurs from inside out. In conclusion, the microwave heating in coffee beans is heterogeneous, starting in its center, favoring the mass transfer phenomenon during drying and can be influenced by the sharpness of the coffee beans edges.

Abstract: The strength of materials is determined by their atomic molecular structure and the process of decay of atomic molecular bonds, which must be taken into account when optimizing materials strength control technologies. The fracture photomicrograph of metal microdamage of welded joint at various moments of time, a multilevel model of flow of acoustic emission signals of materials are presented. The physical meaning, the scale level of parameters included in the model are revealed. The structure of the mathematical model of the flow of AE signals with components of its informative elements of different scale level by strength characteristics of structural materials and resource of technical objects is shown. The multilevel model of the AE signal flow is hierarchically structured, obtained by generalizing deterministic-statistical variability. It describes the process of randomly recording deterministic accumulated damages in the material both before and after the formation of a crack at the stage of waiting for its next leap. It is shown that the proposed nanotechnology of strength control of materials is reduced to non-destructive determination of parameters of prognostic homogeneous destruction, identification of which is based on multilevel modeling of time dependence of micro-crack formation, formulation of criterion of strength homogeneity, registration of AE parameters related to the model of a specific product, which can be automated processing of registration results and determination of universal strength nanoconstants from already published reference data of fatigue tests of standard material samples.

Abstract: The hydrophilic-hydrophobic surface area of alumina powder (Al₂O₃) oxidized at different temperatures was determined on the base of adsorption of water and butane vapor at 25°C. In the order to study the influence of thermal oxidation upon hydrophilic/hydrophobic character of the surface, samples of Al₂O₃ were characterized using granulometry, SEM and BET surface area measurement. SEM results showed that the thermal treatment does not affect the morphology of the Alunima. However, the increase of treatment temperature from 250 to 900°C results in changing of the hydrophilic-hydrophobic balance of Al₂O₃ surface.

Abstract: The research objective is to determine the genesis of productive sediments in the AS₈, BS₁, and YUS₂ reservoirs and reveal the peculiarities of their forming. The identification of facies complexes in productive sediments was carried out with the help of facial and electrometric methods of investigation.

Abstract: The aim of this analysis was to identify the cause of poor corrosion resistance of final product, after the slight change of heat treatment of initial material. Although the hardness of material prior and after the change was the same, significant difference in microstructure was revealed by microstructural analysis. Change in heat treatment process led to heterogeneous distribution of precipitates and increase in the precipitate size which caused deterioration in corrosion resistance. Based on the findings, further optimization of heat treatment was suggested. More importantly, initial material inspection based on microstructural analysis, not only mechanical testing, was recommended.

Abstract: The evaluation of heterogeneous materials used in civil engineering on the microscopic level has become important aspect in proper understanding of the macroscopic behavior of the material. This contribution aims at advantages and problems related to the technique of grid indentation and at the evaluation of mechanical properties.

Abstract: The article discusses the problem related to the calculation of a thick-walled concrete hemispherical shell reinforced in the circumferential direction as well as in the meridian direction. The reduced stiffness in the meridian direction is variable. Thus the shell is considered anisotropic and inhomogeneous. The problem was solved in the variational-difference formulation.

Abstract: Experiments were conducted to investigate deformation-induced processes during in-situ tensile test at elevated temperature. Consequently the microstructure after creep loading was examined by 3D Electron Back Scatter Diffraction (EBSD) technique. The billets of coarse-grained copper were processed by equal-channel angular pressing (ECAP) at room temperature using a die that had an internal angle of 90° between the two parts of the channel and an outer arc of curvature of ~ 20°, where these two parts intersect. The pressing speed was 10 mm/min. To obtain an ultrafine-grained (UFG) material, the billets were subsequently pressed by route Bc by 8 ECAP passes to give the mean grain size ~ 0.7 μm. The constant strain-rate test in tension was performed at 473 K using testing GATAN stage Microtest 2000EW with EH 2000 heated grips which is configured for in-situ electron back scatter diffraction (EBSD) observations. Microstructure was examined by FEG-SEM TESCAN MIRA 3 XM equipped by EBSD detector HKL NordlysMax from OXFORD INSTRUMENT. The tensile test was interrupted by fast stress reductions after different deformation step and observation of microstructure changes was performed. Despite of a considerable interest in ECAP processing method, there are not many works documenting microstructure evolution and changes during creep testing and determining creep mechanisms of ultrafine-grained materials processed by ECAP. It was found that creep resistance of UFG pure Al and Cu is considerably improved after one ECAP pass in comparison with coarse grained material, however, further repetitive pressing leads to a noticeable deterioration in creep properties of ECAP material. Recently it was observed the coarsening of the grains in microstructure of ECAP copper during creep at elevated temperature. It was suggested that creep behaviour is controlled by storage and dynamic recovery of dislocations at high-angle boundaries. In the present work was found that ultrafine-grained microstructure is instable and significant grain growth has already occurred during heating to the testing temperature. Static recrystallization during heating led to the formation of high fraction of special boundaries Σ3 and Σ9. The tensile deformation at 473 K led to the additional grain growth and formation of new grains. Microstructure was investigated also by 3D EBSD.

Abstract: We studied basic structural elements of a deformation relief formed on lateral faces of nickel single crystals under compression. We correlated deformation heterogeneity with the type of structural elements of the relief. It was revealed that deformation heterogeneity did not depend on the type of a relief element or its scale. In addition, some studies were carried out to define ways of the deformation process in slip bands, mesa-and macrobands of deformation as well as in folds. It was found that a slip developed in separate slip bands resulted in their merging into micropackets with a slip occurring concurrently in several parallel planes. It led to the formation of a mesa-or macroscopic element of the deformation relief. We observed both intrusion and extrusion in the material in macrobands of [111]-single crystals as well as the formation of folding areas discussed.

Abstract: This paper shows that non-linearity of mechanical behaviour of metal in the elastic regime has an influence on the forming process. Discrete Dislocation Dynamics simulations show that pure elastic behaviour is altered when reversible dislocation displacements occur even in the very beginning of the elastic stage. The influence of such a non-linearity has an impact on the results of numerical simulations of industrial forming of very thin metal sheets of copper.