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This issue of the RECENT journal was edited with the support of: CONTENTS
Prediction of the Distortions for a 6061 Aluminium Alloy Plate during Quenching Process by Using Mathematical Modellinghttps://doi.org/10.31926/RECENT.2020.62.094 Abstract Quenching of aluminium alloys is a complex thermo-mechano-metallurgical problem due to high non-linearity and the multiphysics character. High residual stresses and distortions are determined by the transient heat conduction problem, plastic behaviour and metallic phase transformations of the aluminium alloy plates during the quenching process. A mathematical model for the structural stresses and distortions was developed and implemented by using ANSYS finite element software. The phase transformations that occur during quenching were not taken into account. The phase transformation problem that occurs during quenching was mathematical modelled through correlation of the heat transfer coefficients with the results obtained for the temperature evolution. Numerical examples are presented for a 6061 aluminium alloy plate with dimensions of 100 x 1500 x 3000 mm. The causes of distortion during quenching process are analysed using the simulation results. The computer modelling offers a support in the understanding the behaviour of the distortions in aluminium alloy plates during quenching and a better control of the process. Keywords ANSYS, spray quenching, distortion, 6061 aluminium alloy
Contribution to the Evaluation of Safety Barriers at the Treatment Section 'STRIPPER'https://doi.org/10.31926/RECENT.2020.62.100 Abstract Algeria occupies an important place in all oil-producing countries. However, in recent years, industrial establishments have experienced a rapid increase in the number of major industrial accidents, where fires and explosions cause serious impacts on people, systems and the environment. In order to avoid these dangerous phenomena, industrialists are obliged to put in place risk control measures whose role is to prevent the occurrence of such phenomena or to limit their consequences. Thus, and because of the unsatisfactory safety results achieved during the past period, The Algerian hydrocarbons company (Sonatrach) has tried to reinforce the security barriers at these industrial sites. From there the objective of this paper appears that is the evaluation of these safety barriers by checking their performances through the development of quantitative or semi-quantitative approaches. This work is devoted to the application of a combination of three methods: HAZOP, ADE and LOPA at the level known as the "Stripper" of the TFT industrial zone. The collection of information on the Stripper system is ensured by the two methods HAZOP and ADE. However, the LOPA method is used to evaluate protective layers whose objective is to control and improve the system's security barriers against future aggressions and undesirable incidents. Keywords HAZOP, LOPA (Layer of Protection Analysis), safety barriers, protection, SIL (Safety Integrity Level), performance criteria, SIS (Safety Instrumented System)
Study on the Assessment and Reduction of Ergonomics Risks in the Construction Fieldhttps://doi.org/10.31926/RECENT.2020.62.112 Abstract At national level it is found that ergonomics at work is not given sufficient importance, such that many employees suffer from musculoskeletal disorders (MSDs). In Romania the insurer, who is also in charge of preventive activities, Ministry of Health through labor medicine, which is in charge of preventive activities as well, and Labor Inspection through Territorial Labor Inspectorates, which have control attributions, did not handle problems regarding ergonomics well enough, such that many disorders of the employees are caused by the fact that ergonomic rules are not respected or taken seriously. The present paper carries out a study on the health and safety of Romanian employees. It mainly considers weight lifting, which is an activity found in all companies, and focuses on assessing ergonomic risks. In this first study, employees working on construction sites in Bucharest, Ilfov County and Brasov County participated. These sites are active for at least 10 months. It was revealed that on most sites ergonomic principles are not considered, but most alarming is that they are not even acknowledged. In this sense, this study aims to identify the ergonomic risks, according to the activities carried out, and then, using QERA method, which was developed within this study, to estimate and assess these risks. Following this assessment, a plan with efficient measures is developed which contains actions for informing, training and raising awareness of the employees and employers regarding ergonomic risks while highlighting the benefits of respecting them. A study prior to applying the measures is made and, after 6 months from the time preventive measures have been implemented, positive results concerning the reduction of ergonomic risks can be observed. This is supported by a reduction in the number of ailments. At the same time, an increase in the productivity and efficiency of workers is observed and it results in a reduction in the number of sick days as well as reduced fluctuations of personnel. Keywords ergonomic risk assessment, risks in the construction sector, security, musculoskeletal disorders (MSD)
Influence of the Polymer Addition in Quenching Water on the Mechanical Properties of Aluminium Alloy Sheetshttps://doi.org/10.31926/RECENT.2020.62.120 Abstract The main method to optimize the mechanical properties of the aluminium alloy sheets during quenching process is the control of the coolant agent. This optimization can be done by controlling the temperature and / or the composition of the coolant. In this work the influence of the composition of the coolant on the mechanical properties was studied by adding polymers. In order to establish the influence of the addition of polymer in the demineralized water on the mechanical properties of the aluminium alloy sheets, several tests were performed with different concentrations of the polymer in demineralized water. The experiments were performed on 6082 aluminium alloy sheets with a thickness of 5 mm. The quenching process of the aluminium alloy sheets was performed by immersion in a stainless-steel vessel with a capacity of 10 litres. The obtained results show that the addition of polymer in demineralized water does not negatively influence the mechanical properties: ultimate tensile strength, yield tensile strength and elongation at break. Keywords quenching, polymer, mechanical properties, aluminium alloy
Experiments on Obtaining Silicified Welded Joints Using Mechanical Vibrationshttps://doi.org/10.31926/RECENT.2020.62.125 Abstract The paper presents the possibility of improving the mechanical properties, of welded parts, subjected to thermochemical silicification treatment. The silicification process depends very much on the carbon content of the silicify welding steel. The silicate layer has a ferrite structure alloyed with silicon. At higher concentrations in silicon, is formed the cementite alloyed with silicon and silicon carbide. This is the reason why it is recommended that low carbon steels should be used for silicification. The chemical reactions in the presence of silicon are complicated and they are depending on the value of the free enthalpy. For this purpose, a program was developed, which allows a quick appreciation of the reaction possibilities, based on thermodynamic calculations. The program can also test, chemical reactions for nitriding and carbonitriding. The welded parts subjected to the silicification treatment have a lower thermally influenced area and lower internal stresses. It has been shown that silicification also improves the protective properties of the surfaces of welded joints in order to eliminate the corrosion process in various corrosion environments. The silicate joint no longer needs to be galvanically coated to withstand corrosive environments. Keywords silicate layer, welded joints, microstructure, diffusion speed, carbon steels
Study of an Industrial Process Using the Correlation Analysishttps://doi.org/10.31926/RECENT.2020.62.130Abstract The work presents a method of analysis specific to statistical processing of a technological industrial process. On the basis of the experimental data produced and recorded from the analysed technological process, the link between two specific variables of the processing process by volumetric electrochemical erosion has been calculated and verified. For the purpose of determining the correlation between process variables, the values obtained in the experimental determination of the basic electrochemical characteristics obtained for a 55VMoCrNi17 matrix steel. This study was conducted based on the determination of the processing parameters: current density j [A/mm2], feed speed vA [mm/min], or front gap s90 [mm]. When estimating the links between the different factors and the status variable (s), the correlation analysis shall be used. Keywords industrial process, correlation, technological variables, Pearson correlation coefficient, volumetric electrochemical erosion
Analysis of the Power of Discrimination between Normal Distribution and Weibull Distribution of the Goodness-of-Fit Testshttps://doi.org/10.31926/RECENT.2020.62.136 Abstract The paper presents and emphasizes the capacity of different goodness-of-fit tests to discriminate between normal distribution and Weibull distribution, from the acceptance of the normality hypothesis point of view. The Weibull and the normal distribution are met frequently in the reliability analysis. The discrimination between these two distributions is difficult by considering the graphical representation of the data considered. The Weibull distribution is accepted as being a normal distribution by some goodness-of-fit tests. Since data analysis is very important in the evaluation of the reliability of a system, it results that it is very important to determine correctly the distribution which describes the data best. On this purpose, goodness of fit tests are to be conducted. The goodness of fit tests which were taken into account are both general goodness-of-fit tests - Kolmogorov-Smirnov, Cramer-von-Mises, Anderson-Darling, and normality goodness-of-fit tests - Lilliefors, Shapiro-Wilk, D'Agostino, Massey, Filliben, Z, Cox. These goodness-of-fit tests are conducted on Weibull distributed data in order to test their power to discriminate between Weibull and normally distributed data. Keywords metrological reliability, goodness-of-fit tests, normal distribution, Weibull distribution
A Framework for Using Photogrammetry in 3D Scanninghttps://doi.org/10.31926/RECENT.2020.62.140 Abstract The paper presents the necessary steps to be completed in order to obtain a 3D model through photogrammetry as an alternative to 3D scan. The methodology described in the paper does not aim to present photogrammetry as a substitute for 3D scan but as a low-cost alternative and/or for occasional use. The framework presented is highlighted by tests performed on an object that has most of the "disadvantages" for the photogrammetry operation. The results are analysed from a technical point of view and correlated to the duration of each stage. This analysis is performed in order to underline the methods and means of improvement. At the same time, the paper presents a structured approach in order to obtain a working 3D model that could be further improved in any CAD software. Keywords photogrammetry, 3D scan, accuracy
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