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Abstract

The present article is dedicated to the study of the vibration properties of metal-based composite materials and the application of the non-destructive testing method. The main modal parameters of the metal-based composites were investigated. For experimental determination of natural frequencies and modes of oscillations, the method of scanning laser Doppler vibrometry was used. For the numerical modal analysis, the finite element method was used. The material model was a layered composite with isotropic linearly elastic layers and metal layers. The task of identifying the material model was considered as the problem of minimising the discrepancy between the calculated natural frequencies and the experimental ones. The developed method can be recommended for the determination of parameters of material models for calculating the modal characteristics of polymer–metal sandwich sheets and metallic mono-materials composite products. Methodology for identifying models of elastic behaviour of polymer–metal composite materials, based on the results of the experimental modal analysis, is presented. Wavelet-based damage detection is also presented as an appropriate approach for the identification of integral conditions of the metal–polymer–metal composite materials. Results of wavelet transform convolutions are presented.

Abstract

During 1984–1997, the ferronickel plant in Drenas used iron-nickel ore from the mines of the Republic of Kosovo: Glavica and Çikatove (Dushkaje and Suke) mines. However, during the years 2007–2017, when the plant started operating from the cessation of production, which was from 1998 to 2007, some types of iron-nickel ores from different countries began to be used, starting from iron-nickel ores from Kosovo, iron-nickel ores from Albania, ores from Indonesia, ores from the Philippines, ores from Guatemala, ores from Turkey and ores from Macedonia. The ore composition, however, is mainly oxide-laterite ore. Iron-nickel ores in the plant are characterised by high moisture content, a very important factor influencing the process of scraping the charge in rotary kilns and presenting in general. Among the iron-nickel ore used in the ferronickel plant, the ores from Albania are characterised due to their low moisture content when compared with the other ores as well as the high content of iron oxides, which affect the temperature rise inside the furnaces, as the iron ores play an important role in the pre-casting process in rotary kilns.

Abstract

Microstructure of austenitic stainless steel is primarily monophasic, i.e. austenitic. However, precipitation of the δ-ferrite in the austenite matrix is possible depending on the chemical composition of steel. δ-Ferrite is stable on room temperature but it transforms into σ-phase, carbides and austenite during heat treatment. In this work, the results of analysis of influence of temperature and time on decomposition of δ-ferrite are presented. Magnetic induction method, microstructure and hardness analyses were used for testing the degree of decomposition of the δ-ferrite. Analysis of results showed that increase in temperature and time increases the degree of decomposition of δ-ferrite.

Abstract

Primary, secondary and accessory minerals in tonalitic rocks from Iwo region of the Precambrian Basement Complex of Southwestern Nigeria were identified and analysed with the aim of determining the various processes involved during the crystallisation of magma. Thin sections of tonalite were prepared and studied with the aid of a petrographic microscope. The mineral assemblages observed are biotite, plagioclase, alkali-feldspar, amphiboles, pyroxene, quartz, muscovite and chlorite. Allanite, titanite, apatite and zircon occur as accessory minerals. Muscovite and chlorite are found to be secondary minerals. The mineral allanite has a characteristic form of zoning and shows evidence of metamictisation, and is surrounded by dark-coloured biotite having radioactive haloes. Titanite is anhedral to subhedral crystals and forms reaction rim round opaque minerals. Plagioclase shows evidence of compositional zoning as well as plastic deformation of the twin lamellae. The allanite observed is primary in nature and has undergone radioactive disintegration; chlorite and muscovite are formed by secondary processes of chloritization and sericitisation, respectively. The tonalite is formed as a result of rapid cooling of magma close to the Earth's surface.

Abstract

In this article, we report the mineral chemistry and petrographic features of charnockitic exposure of Iboropa within Precambrian Basement Complex of Nigeria. The mineral assemblages are pyroxene, plagioclase, biotite, hornblende, alkali feldspars, microperthite, quartz and ilmenite, with apatite occurring as accessory mineral. Apatite occurs in abundance as euhedral crystals. Orthopyroxene observed is strongly pleochroic and has numerous microfractures, and it is hypersthene (En45Fs54Wo1) with low TiO2 and MnO, having extremely low percentage of CaO. Hypersthene is mantled by a complex corona of amphibole, and the amphibole is hornblende with a chemical formula: (K,Na)(Ca,Fe)2 (Fe,Mg,Al,Ti)5(Al,Si)8O22(OH)2. Plagioclase occurs as inclusions in both pyroxene and biotite. Biotite has high concentration of TiO2 and extremely low CaO. The opaque mineral observed is ilmenite and it is concentrated around hypersthene and amphibole. Rare earth element (REE) displays negative Eu anomaly with enrichment of light REE over heavy REE. Amphiboles surrounding orthopyroxene are evidences of retrograde reactions and are formed at the expense of orthopyroxene reacting with plagioclase and quartz in the presence of fluid. The relationship between the mineral assemblages suggests the retrogression of the gneiss that might be as a result of rehydration process, and it is a transition from granulite facies to amphibolite facies during a retrogressive form of metamorphism.

Abstract

Subsurface information on source rock potential of the Eocene shale unit of the Abakaliki Fold Belt is limited and has not been widely discussed. The total organic carbon (TOC) content and results of rock-eval pyrolysis for nine shale samples, as well as the one-dimensional (1D) geochemical model, from an exploration well in the Abakaliki Fold Belt were used to evaluate the source rock potentials and timing of hydrocarbon generation of Lower Eocene source rocks. The TOC content values of all the samples exceeded the minimum threshold value of 0.5 wt.% required for potential source rocks. A pseudo-Van Krevelen plot for the shale samples indicated Type II–III organic matter capable of generating gaseous hydrocarbon at thermally mature subsurface levels. The 1D burial model suggests that the Eocene source rock is capable of generating oil and gas at the present time. The modelled transformation ratio trend indicates that a fair amount of hydrocarbon has been expelled from the source rocks. The results of this study indicate that the Eocene source units may have charged the overlying thin Eocene sand bodies of the Abakaliki Fold Belt.

Abstract

The study integrates geophysical and geotechnical methods for subsoil evaluation and shallow foundation design. The study involved six vertical electrical sounding and geotechnical investigation involving cone penetration test and laboratory soil analysis. Three major geologic units were delineated; the topsoil, weathered layer and partly weathered/fractured/fresh bedrock. The overburden thickness is in between 15.2–32.9 m. Based on resistivity (16–890 ohm-m) and thickness (12.7–32 m) the weathered layer is competent to distribute structural load to underlying soil/rock. The groundwater level varies from 4.5 to 12.3 m. Therefore an average allowable bearing capacity of 200 kPa is recommended and would be appropriate for design of shallow foundation in the area, at a depth not less than 1.0 m with an expected settlement ranging from 9.03–48.20 mm. The ultimate bearing and allowable bearing capacity for depth levels of 1–3 m vary from 1403–2666 kPa and 468–889 kPa for strip footing while square footing varies in between 1956–3489 kPa and 652–1163 kPa respectively.

Abstract

In this article, we have investigated a fitting proposal model for calculating the crystallite size of pure NiO thin films by varying the structural parameters, such as full width at half-maximum β, lattice parameter a and differences in aa 0. The experimental data of NiO thin films were prepared at several deposition temperatures in the range of 380–460°C. All estimated values of crystallite sizes are proportional to the experimental data. Thus, the measurement of the crystallite size values by this proposed model is compatible with practical measurements qualitative.