Seminar
MECHANICS OF MACHINES AND MECHANISMS - MODELS AND MATHEMATICAL METHODS

 

PROGRAM

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Plan rada Seminara Mehanika mašina i mehanizama - modeli i matematičke metode za JANUAR 2020.

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UTORAK, 21.01.2020. u 17:00, Sala 301f, MI SANU, Kneza Mihaila 36
Julijana Simonović, Faculty of Mechanical Engineering, University of Nis, Serbia
MATHEMATICAL MODEL OF EXTERNALY EXCITED BONE ADAPTATION
Based on bone mechanobiology research, this paper develops computational analytical models in order to address and better understand mechanotransduction - the molecular mechanisms by which bone cells sense and respond to mechanical signals. Downstream autocrine and paracrine signalling in response to periodic excitation were modelled by cell population system of ordinary differential equations in order to better represent and predict long-term behaviour and consequences of bone cell loading. Different mathematical tools were exploited to suggest the expected parameters value ranges. The comparison with in-vivo co-culture cell experiments readouts gave the reasonable, promising and credible conclusion.
Methods: A Bio-Mathematical-model has a dual interpretation. The mathematical expression bears meaning by itself without referring to the biological reality. It can be interpreted, analyzed, and used in computational simulations without knowing what it represents. However, a bio-model is more than a pure syntactical formal expression: it describes a piece of biological reality- a cycle of bone remodeling. The processes included in the model should be significantly precise with all aspects (inputs I, outcomes O, time T, resources R, controls C and preconditions P), to be amenable to mathematical formalization. A functional bio-model establishes a mapping between these two conceptual sides. The S-system (the generalized Lottka-Volterra system) is in charge and is solved deterministically together with its stochastic analog (Gillespie algorithm) used for noise check and system behavior dynamics analysis.
Results: Equations of bone turnover balance between bone resorption and formation together with time changes of bone resorbing and forming cells numbers form the mathematical model of system of ordinary differential equations (ODEs). Population dynamics are illustrated using time series plots, phase portraits, histograms and bifurcation diagrams. In-silico experimenting with a number of osteocytes up to or around a certain threshold allows us to distinguish and describe different dynamics and relations between involved cells. The external signal can be considered as an additional term affecting the number of responding OCy or as the functional periodicity of power low coefficients affecting autocrine signalling of OB.
Conclusion: Mathematical models are a great way of cementing biological verbal models. Specifically, they can provide causative mechanisms linking inputs and outputs and illuminating underlying assumptions that determine a biological system’s dynamics. Finally, they offer a means of predicting new outcomes, as well as highlighting the most sensitive modelled components, resulting in the construction of new experimental hypotheses and reducing experimental waste.

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UTORAK, 28.01.2020. u 16:00, Sala 301f, MI SANU, Kneza Mihaila 36
Guest organizer – dr Olivera Erić Cekić, Associate Research Professor, Innovation center of the Faculty of Mechanical Engineering, University of Belgrade
THEMATIC SESSION - NEW TRENDS IN MECHANICS OF MATERIALS AND RELATED TOPICS

Lectures:
Prof. Sebastijan Baloš, Faculty of Technical Sciences, University of Novi Sad
APPLICATION OF NANO PARTICLES IN SHIELDED METAL ARC WELDING AND HARDFACING
Titanium dioxide (TiO₂) is traditionally used for a wide range of applications, from white pigment in paints and varnishes, as a coating in fiber-optic cables, to photocatalitic coatings, as well as the applications as fillers for a wide range of materials. Recently, TiO₂ nano particles were envisaged as a promising way to improve the properties of welds and hardfaced layers. In this paper, the application of TiO₂ nano particles for welding and hardfacing is presented.
Nano particles were introduced in shielded metal arc welding (SMAW) electrodes by infiltration into the coating of the electrodes. At temperatures of around 4000℃, dissociation of TiO₂ occurs. When the temperature falls to the critical level, titanium oxides occur again, suspected to be Ti₂O₃ representing inoculants that influence grain refinement. Inoculants of complex nature occur, having titanium oxide and manganese oxide components in the central section and silicon oxide in periphery of the complex oxide. The number of the inoculants increases, their size decreases and grain refinement occurs in welded specimens. As a consequence, in welded specimens, grain refinement influences the increase in content of acicular ferrite in weld metal and the decrease of the content of Widmanstaetten ferrite. This way, the strength, hardness and ductility of welds can be improved, by using both cellulose and rutile electrodes.
In hardfaced specimens, microhardness in subsurface layers increases, due to the increased hard particle content and decreased distance between complex carbide hard particles around dendrites and their orientation at depths of over 0.5 mm. Besides dendrite refiner, titanium oxides themselves increase the wear resistance of the resulting layer, increasing life of the component obtained by hardfacing by using modified versus the layers obtained with unmodified electrodes.
In all, nano particles can be viewed as a beneficial factor in increasing of the performance of SMAW electrodes.

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dr Mišo Bjelić, Faculty of Mechanical and Civil Engineering in Kraljevo, University of Kragujevac, Serbia
NUMERICAL SIMULATION OF THE WELDING PROCESS: APPLICATION TO THE DESIGN OF WELD BEAD GEOMETRY AND MECHANICAL PROPERTIES
Requirements for increased productivity have led to the need for automation of welding processes. Successful automation of such processes is connected to the possibility of process parameters estimation regarding weld bead geometry, mechanical properties of welded joints, etc.
Simulation model of the welding process can give us an insight into the influence of welding parameters on temperature field during welding and through it and the influence on geometry, microstructure and mechanical properties of welded joints. As such, it can be used in reverse direction, to find correct values of welding parameters that give required weld geometry and mechanical properties. This lecture gives insight into the methodology of the numerical modeling of heat transfer during welding as well as its coupling with the models of austenite decomposition through the cooling stage of the welding process to estimate mechanical properties of welded joints. A part of the lecture is dedicated to the calibration of the simulation model in order to overcome the uncertainty of input data. The last part concerns with a determination of the GMAW parameters, using optimization methods. Experimental verification has shown that the developed models and methodologies represent a reliable way for the design of weld bead geometry and mechanical properties.

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dr Miroslav Dramićanin, Faculty of Technical Sciences, University of Novi Sad
ACTIVATED FLUX FOR A-TIG WELDING OF STAINLESS STEEL
Welding is a joining technology of two or more, similar or dissimilar materials. Tungsten inner gas (TIG) is a well-established and renown welding process that can produce high quality welds on different materials, including various stainless steels, and a number of non-ferrous alloys but this process is relatively slow with low productivity. To resolve the problem of relatively low productivity, activated TIG (A-TIG) was developed by Gurevich et al., during the 1960s at the Paton Welding Institute in Kiev Ukraine. In this welding process, a flux (oxide coating) is sprayed or applied with a brush over the cleaned and prepared surface to be welded. Fluxes were fabricated by mixing, usually metallic oxide powders with solvents, most frequently solvents were acetone and ethanol.
In this paper, the selection of solvent, size, type and the content of oxide particles in activated flux aimed at increasing the penetration on austenitic stainless steel in gas tungsten arc welding is investigated. In addition to the activated flux composition in paper were selected the welding parameters that result the highest penetration depth. The varied parameters were electrode geometry, welding current and welding speed. After the selection of successfully activated flux formulations and welding parameters, the characterization of mechanical properties was done, and chemical composition and microstructure were determined.
The advantages of using oxide coatings in the A-TIG welding process are multiple: V-preparation of the base metal can be avoided; instead, I-preparation can be used; single pass welding can be sufficient, resulting in significant gas savings as well as unnecessary use of consumables materials, thereby reducing the cost of the welding process.

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dr Jelena Gulicovski, Laboratory for Materials Sciences, Institute of Nuclear Sciences Vinča, University of Belgrade
PROTECTIVE ABILITY OF CERIA AS PROTECTIVE COATING ON ALUMINIUM
Ceria coating is formed on Al from the ceria sol prepared exclusively by forced hydrolysis of Ce(NO₃)₄, in order to test their ability to protect Al from corrosion. The characterization of sol–gel-processed ceria coating and coating/Al assembly brings new issues on Al corrosion and protection caused by unique properties of the sol–gel coating. The corrosion behaviour of bare Al and Al/CeO₂ is investigated by the electrochemical impedance spectroscopy (EIS) during the exposure to NaCl aqueous solution. The morphology and composition of the samples are examined by scanning electron microscopy and energy dispersive spectroscopy. EIS data showed greater corrosion resistance of CeO₂-coated aluminium in comparison to bare Al at long exposure times. CeO₂ coating does not hinder completely the corrosion processes on Al. The Al beneath CeO₂ coating is subjected to intrinsic formation of a uniform protective coating/Al interphase, cross-linked by AlO(OH) fibre-like structures. They appear created by corrosive medium from the coating reversely gelled by NaCl solution. As the fibre network is created during exposure, Al becomes better protected than by spontaneous formation of porous passive layer of Al(OH)₃ on bare aluminium. Sol–gel ceria coatings thus improve corrosion resistance of aluminium during prolonged exposure to corrosive medium.

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Seminar Mehanika mašina i mehanizama - modeli i matematičke metode započeo je sa radom u junu 2018.god. Seminar se održava do dva puta mesečno, utorkom u periodu od 17.00 - 19.00 u Matematičkom institutu SANU.

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