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Effect of microtemperatures for micropolar thermoelastic bodies
Marin Marin,Dumitru Baleanu,Sorin Vlase 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.61 No.3
In this paper we investigate the theory of micropolar thermoelastic bodies whose micro-particles possess microtemperatures. We transform the mixed initial boundary value problem into a temporally evolutionary equation on a Hilbert space and after that we prove the existence and uniqueness of the solution. We also approach the study of the continuous dependence of solution upon initial data and loads.
Relaxed Saint-Venant principle for thermoelastic micropolar diffusion
Marin Marin,Ibrahim Abbas,Rajneesh Kumar 국제구조공학회 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.51 No.4
The main goal of this study is to extend the domain of influence result to cover the micropolar thermoelastic diffusion. So, we prove that for a finite time t>0 the displacement field ui, the microrotation vector φi, the temperature θ and the chemical potential P generate no disturbance outside a bounded domain Bt.
Structural and optical characterization of solegel derived Tm-doped BaTiO3 nanopowders and ceramics
Marin Cernea,Corina Elisabeta Secu,Bogdan Stefan Vasile,Mihail Secu 한국물리학회 2013 Current Applied Physics Vol.13 No.1
Nanocrystalline Tm3þ(5%)-doped BaTiO3 (BT-Tm) has been synthesized by the solegel method. The morphology, structure, and optical properties of powders and ceramics were characterized. The average grain size of the gel precursor annealed at 700 and 900 ℃ was 20 nm and 30 nm, respectively. These powders were single phase and crystallized with a cubic structure while the BT-Tm sintered ceramics were crystallized with the tetragonal BaTiO3 structure. The photoluminescence spectra showed typical transitions of Tm3þ ions and a structure consistent with the Tm3þ ions incorporation in the BaTiO3 crystalline lattice. Thermoluminescence peaks recorded at 300 ℃ (for annealed samples) or at 230 ℃ for the ceramic sample were assigned to the recombination of the Tm2þ-electron traps located mainly at the surface of the nano-crystals or inside the microcrystals, respectively.
Evolutionary multi-objective optimization of energy efficiency in electrical discharge machining
Marin Gostimirovic,Vladimir Pucovsky,Milenko Sekulic,Miroslav Radovanovic,Milos Madic 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.10
Electrical energy, which in the machining zone is transformed into heat, is of key importance in electrical discharge machining (EDM). Machining performance of EDM is determined by the characteristic of discharge energy. Therefore, an experimental-analytical approach of discharge energy efficiency was analyzed. The main input parameters for controlling the discharge energy are discharge current and discharge duration. The EDM process is monitored considering the two output machining performance, i.e., material removal rate and surface roughness, which are important for increasing productivity and quality. We modeled the energy efficiency of electrical discharge machining by the use of genetic algorithm. With this action an attempt was made to find even more precise dependence of discharge energy parameters with machining performance. Finally, this was followed by optimization of the discharge energy efficiency in EDM process using multi-objective approach. Evolutionary two-objective optimization is leading to the set of optimal solutions for the discharge energy considering the two machining parameters. Using this set of solutions, EDM discharge energy parameters can be selected to achieve high material removal rate with good surface roughness.
Influence of discharge energy on machining characteristics in EDM
Marin Gostimirovic,Pavel Kovac,Milenko Sekulic,Branko Skoric 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.1
The machining characteristics of electrical discharge machining (EDM) directly depend on the discharge energy which is transformed into thermal energy in the discharge zone. The generated heat leads to high temperature, resulting in local melting and evaporation of workpiece material. However, the high temperature also impacts various physical and chemical properties of the tool and workpiece. This is why extensive knowledge of development and transformation of electrical energy into heat is of key importance in EDM. Based on the previous investigations, analytical dependence was established between the discharge energy parameters and the heat source characteristics in this paper. In addition, the thermal properties of the discharged energy were experimentally investigated and their influence on material removal rate, gap distance, surface roughness and recast layer was established. The experiments were conducted using copper electrode while varying discharge current and pulse duration. Analysis and experimental research conducted in this paper allow efficient selection of relevant parameters of discharge energy for the selection of most favorable EDM machining conditions.
Accuracy of structural computation on simplified shape
Marin, P. Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.35 No.2
This paper focuses on a number of criteria that enable controlling the influence of geometric simplification on the quality of finite element (FE) computations. To perform the mechanical simulation of a component, the corresponding geometric model typically needs to be simplified in accordance with hypotheses adopted regarding the component's mechanical behaviour. The method presented herein serves to compute an a posteriori indicator for the purpose of estimating the significance of each feature removal. This method can be used as part of an adaptive process of geometric simplification. If a shape detail removed during the shape simplification process proves to be influential on mechanical behaviour, the particular detail can then be reinserted into the simplified model, thus making it possible to readapt the initial simulation model. The fields of application for such a method are: static problems involving linear elastic behaviour, and linear thermal problems with stationary conduction.