International Journal of Materials
E-ISSN: 2313-0555
Volume 5, 2018
Notice: As of 2014 and for the forthcoming years, the publication frequency/periodicity of NAUN Journals is adapted to the 'continuously updated' model. What this means is that instead of being separated into issues, new papers will be added on a continuous basis, allowing a more regular flow and shorter publication times. The papers will appear in reverse order, therefore the most recent one will be on top.
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Volume 5, 2018
Title of the Paper: The Geo-Radar in the Service of Concrete Durability
Authors: K. Hadja, F. Kharchi
Pages: 41-46
Abstract: Concrete has became a universal building material. Its mechanical resistance was considered as a basic criterion. It appears today that the concrete can be affected by its environment. Its performances decrease when it is exposed to moisture, pollution and other aggressive substances such as chlorides and sulfates. Therefore, the concrete degrades and the steel bars corrode. Aggressive substances are generally conveyed by water. Thus, the water content is a good indicator of the durability of concrete. Non-destructive methods has been developed for diagnosing the state of a structure at any time, which allows monitoring and preventive maintenance work. The Radar technic is one of the buildings auscultation techniques which can be used. It is an application of electromagnetism and was mainly used to find buried objects in concrete and for the recognition of discontinuities or geometries. Relatively recent research has shown that the radar can also be used as a tool for characterizing the state of the material. This enables new application fields. The radar signal is analyzed in terms of mitigation and speed, by the use of different reflected signals and also the direct wave signal between transmitter and receiver. The measurements made in the laboratory or on site indicate the sensitivity of this signal to the desired settings. The radar allows locating steel bars, measure concrete cover and estimate moisture concrete. The propagation speed is directly related to the dielectric constant. This measure gives an idea about the actual concrete moisture condition. Analyses of radar profiles obtained by immediate auscultation of structures, Provides an idea about the anomalies related to the concrete: corrosion, presence of chlorides and other anomalies related to improper repair of the concrete or an accumulation of water above the element studied.
Title of the Paper: Amorphous Superhard and Functionally Unique Materials Developed on Granulation Using Controlled Film Flow Decay
Authors: Іvan V. Kazachkov
Pages: 35-40
Abstract: The specific granulation problem is presented, which has concern to the controlled liquid metal jet and film flows for a production of the uniform by size and form particles (granules) cooled with a high rate, to be amorphous or close to the amorphous materials. Basics of the developed theory of the controlled jet and film flow disintegration with further rapid cooling of the drops after disintegration of film flow are presented together with the new patented granulation devices developed and tested. The original methods and devices can be used for production of the amorphous granules in a wide range of the given sizes, with a very narrow (plus-minus 50%) deviation in size.
Title of the Paper: Experimental Evaluation of Temperature History in Friction Stir Processing of as-cast Magnesium Alloy
Authors: Arash Rostami
Pages: 25-34
Abstract: Friction stir processing (FSP), based on friction stir welding (FSW), is a thermo mechanical process for modifying the microstructural and mechanical properties of sheet metals and as-cast alloys. FSP also can be used for mechanical alloying and producing metal matrix composites. Having hexagonal close packed (hcp) structure and dendritic Mg12Al17 precipitations in grain boundaries, AZ91 magnesium alloy is a brittle metal. Due to creation of longitudinal cracks and tunneling cavities throughout the processing path, FSP of AZ91 is difficult and also sensitive to processing temperature. In this study, effect of processing parameters such as the rotational and traverse speeds and pin size on the temperature history experienced by material was investigated. Additionally, a minimum temperature required to produce a defect-free specimen is presented.
Title of the Paper: Graphite Inserts for Management of Thermal Conductivity in Phase Change Materials – Performances and Limitations
Authors: Bogdan Diaconu, Mihai Cruceru, Lucica Anghelescu
Pages: 19-24
Abstract: Phase Change Materials (PCMs) have been used recently in applications where the supply is not synchronous with the demand in order to act as a buffer between the two and compensate the random variations of each. PCMs store and then release considerable amounts of heat without significant temperature variation. Their key property is the latent heat of fusion/solidification and the main point that has to be considered in the design of the application is the match between the melting point and operating temperature. Thus, the main mode in which heat is stored in the PCM is latent heat and a relatively small part is sensible heat. However, the main limitation in the applicability of PCMs is their value of the thermal conductivity coefficient. This rises various design constraints which eventually result in limited applications. Various methods exist to enhance the conduction heat transfer in PCMs. The paper presents a discussion on techniques, performances and limitations of graphite insertion to boost PCMs thermal conductivity. The main goals of the paper are (1) to demonstrate that although graphite inserts are beneficial in increasing the overall efficiency of a PCM – based thermal management system and (2) a number of limitations, side effects and factors that adversely influence the heat conductivity increase exist and must be accounted for by performing an overall optimization of the thermal management system under constraints dictated by functional requirements.
Title of the Paper: Simulations of Liquid Metal Flows by DNS CONV-3D Code
Authors: Vladimir V. Chudanov, Anna E. Aksenova, Valerii A. Pervichko
Pages: 13-18
Abstract: To simulate the thermal hydraulics processes in fast reactors with a liquid metal coolant DNS CFD code CONV-3D has been developed. The paper presents the results of the application of CONV-3D code for simulation of sodium natural convection in the upper plenum of the MONJU (Japan) reactor vessel, the calculation results of the experiment conducted on the Phenix facility (France) with sodium coolant, mixing of sodium flows with different temperatures in the T-tube (Russia). The results of simulation of heavy-liquid metal (LBE) flow and heat transfer along a hexagonal 19-rod bundle with wire spacers (KALLA, Germany) are presented also. A satisfactory agreement of the numerical predictions with experiments is demonstrated, in particular for the temperature distribution vs the coordinates. The results obtained allow to conclude that using of CONV-3D code with high predictive power can be recommended for reactor applications.
Title of the Paper: Prediction of Effective Mechanical Properties of Composite Materials Using Homogenization Approach: Application to Tungsten Fiber Reinforced Bulk Metallic Glass Matrix Composite
Authors: Soufiane Belhouideg
Pages: 8-12
Abstract: In this paper, the homogenization approach was presented to predict the effective mechanical properties of heterogeneous materials such as composite materials. Indeed, the main idea of this approach is to characterize the effective mechanical properties from a microstructural description of the heterogeneous materials and the knowledge of the local behavior of constituents using the homogenization process. It is a very efficient tool which is intensively developed in the field of numerical simulation of heterogeneous materials. Different scheme established from the solution of Eshelby’s inclusion problem are recalled such as Mori-Tanaka scheme, dilute scheme and Voigt and Reuss bounds. Homogenization approach was applied to estimate the effective mechanical properties of tungsten fiber reinforced bulk metallic glass matrix composite. Predicted values were confronted with those obtained by experimental approach from literature. These comparisons show good agreement between the predicted and experimental values. The maximum deviations remain lower than 10.5% using Voigt bound. A parametric study shows that the mechanical properties depend strongly on the shape of inclusions.
Title of the Paper: Effect of Organic Solvents in Morphology and Mechanical Properties of Electrospun Polyvinylpyrrolidone Fibers
Authors: Christian Narváez-Muñoz, Nathaly Villacís, Diego Narváez, Karla Vizuete, Carlos Arroyo
Pages: 1-7
Abstract: In this work, the electrospinning technique was used to obtain fibers for mechanical characterization. polyvinylpyrrolidone (PVP) was combined with organic solvents (ethanol and dimethylformamide (DMF)) to generate solutions, looking for the appropriate parameters to obtain fibers with the best morphology and the best mechanical properties. Starting from previous investigations to find the adequate percentages of solvent and PVP, several solutions were made, varying the different parameters like voltage, flow, tip collector distance. Seeking to obtain acceptable samples, the diameter was measured in a scanning electron microscope (SEM). The elastic modulus was measured for the fibers with the best aspect. Mechanical properties were measured in an atomic force microscope (AFM) with the Hertz contact method and the data were approximated to its mathematical model. The solutions that resulted in the best morphological properties were: ethanol - 8% PVP, DMF – 14% PVP, 70% ethanol - 30% DMF - 8% PVP, with diameters in the micrometer range of 1.6, 1.22 and 1.35 respectively, and elastic modulus of 40.08 MPa, 8.8 MPa and 32.78 MPa correspondingly. An analysis of all the parameters influencing the process was performed and an analysis of the influence of the solvents, based on the data of the elastic moduli was carried out.
