Achievements and Solutions in Mechanical Engineering

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Authors: Radu Velicu, Lenard Jurj, Radu Saulescu
Abstract: The literature on chain and belt transmissions talks about the effect of centrifugal forces on chains and belts as creating a constant Fc = (m/l) v2 constant component along belt or chain. This component is only depending on the mass per unit of length (m/l) and the velocity of chain or belt. Our experimental data and also theoretical approach on the centrifugal effect on the load of chain and belt transmissions shows that chain/belt supplementary loading but also shaft unloading are different. This effect must consider not only the mass per unit of length and the velocity of chain/belt but also the stiffness of chain/belt and the stiffness of shafts and other bearing components. The conclusions of this paper are changing significantly the recommendations from the literature about the centrifugal effect on the load of chain and belt transmissions.
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Authors: Radu Papuc, Mihai Tiberiu Lates, Radu Velicu
Abstract: This paper addresses the mathematical modeling of the normal force distribution and the contact pressure between the toothed chain links and the tensioning guide. Next, it is highlighted the pressure distribution exercited on the lubricant film on the contact width, using the Reynolds equation. At the end of the paper there are presented the conclusions referring to the transition between the mixed lubrification and hidrodynamic one for the contact between guide and toothed chain links.
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Authors: Radu Velicu, Radu Saulescu, Mihai Tiberiu Lates
Abstract: The chain drive transmissions are used mainly in the automotive industry as distribution transmissions in cars. In the specific literature, the kinematics and the dynamic analysis problems are accomplished depending on the European and American standards. The contact between the chain’s bush and the chain wheel is influencing the transmissions dynamics and is influenced directly by its geometry. According to these, the paper presents the influence of the chain wheel’s geometry on the contact angle which depends on the point’s position where the normal and transversal forces are acting.
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Authors: Lenard Jurj, Radu Saulescu, Radu Velicu
Abstract: The aim of this paper is to define and to analyse the theoretical contact forces that appear in a sprocket - silent chain joint. The contact force between the links and the teeth flanks of the sprocket can be considered as a reaction to the axial force in chain (tensioning force), transmitted throughout the pin - links joints. Friction forces will be considered in the joints and in the link - sprocket joints, which will be defined by the corresponding friction angles. The centrifugal force is also considered. This paper is presenting the steps to obtain the analytical model for the forces from the sprocket - link and the pin - link joints, depending on the tensioning force and the centrifugal force. These forces are computed in order to establish their distribution along links.
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Authors: Masakazu Haga, Tsuyoshi Kondo, Takayuki Hamauchi
Abstract: Flow patterns and temperature distributions of buoyancy–Marangoni convection in a liquid were analyzed both experimentally and theoretically. We focused on two-dimensional natural convection in a horizontal liquid layer. In the experiment, silicone oil (with a viscosity of 1 × 10−5 m2/s) was used as a test liquid and the temperature and velocity fields were visualized using liquid crystal capsules. The visualization experiment included cases of both steady flow and oscillatory flow. In the case of a deep liquid layer, an oscillatory flow with repeated acceleration and deceleration occurred due to the interaction of the buoyancy convection and the Marangoni convection; however, this did not occur when the liquid layer was shallow. In the numerical calculation, the governing equations of buoyancy–Marangoni convection were solved using a finite difference method. The numerical calculation results demonstrate that the position of the downward flow due to buoyancy convection was changed by the Marangoni convection, which agreed with the experimental result.
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Authors: Ionut Geonea, Nicolae Dumitru, Alexandru Margine, Petre Cristian Copilusi
Abstract: In this research an experimental test rig and method to measure friction torque from screw-nut assemblies is presented. The experimental test rig uses to measure friction torque an elastic cylinder bush with strain gauge transducers. The frictions torque and the traction force from the threaded assembly are transmitted to the elastic cylinder bush and produce elastic deformations. The elastic cylinder is calibrated in order to establish a correlation between elastic deformation and force of solicitation. In order to measure the experimental data the MGCPlus data acquisition system is used. The experimental results obtained are presented, consisting in the dependence between friction torques and axial traction force occurred in the screw.
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Authors: Mihai Ţălu, Daniela Vintilă, Laura Diana Grigorie, Ştefan Ţălu
Abstract: This paper presents a computer software application (using the Maple programming language) together with numerical applications which allow the determination of the pressure drop uniformly distributed in the pipes with circular-eccentric section, which appears in the case of critical transition flow subdomain I.
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Authors: Leonard Ciurezu-Gherghe, Nicolae Dumitru, Petre Cristian Copilusi
Abstract: In this paper is presented a few models of a robotic snake like unit which can be used in Minimally Invasive Surgery (MIS). In particular, this paper focuses on the flexible unit details. It’s rigid links can be fabricated using selective materials that are light-weight and slim. Thus, this flexible unit can be inserted through one small cavity. Finally, we show that the selected flexible unit may be a very good alternative for Single Port Access (SPA) surgery or this can be used in other environments as well.
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Authors: Valcu Roşca, Cosmin Mihai Miriţoiu
Abstract: The products materials failure process subjected to a time variable loading can be watched and controlled through the study of an important parameter from the “Fracture Mechanics” given by the crack growth rate or the cracking rate. This is marked with da/dN, sometimes da/dt, representing the length variation a at a fatigue loading cycle. From the most used models for its study, one can remember: methods that use the American standards ASTM, Paris formula model or the Walker one. The model called NASGRO or FNK is used to study the crack growth evolution in NASA studies, being a more complex method, for the cracking process. The results obtained were compared to the ones determined with the above methods. For the tests, steel samples R520 were used, CT type, with side notch. The loading cycle was made with the asymmetry coefficient R= 0.5, at the temperatures: 293K, 252K and 213K.
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