Advanced Concepts in Mechanical Engineering I

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Authors: Liviu Andrusca, Ioan Doroftei, Paul Doru Barsanescu, Viorel Goanta
Abstract: Determination of materials behavior subjected to complex stress state corresponding to certain operating conditions is one of the main objectives of material testing. Biaxial and triaxial tests are necessary to facilitate understanding of the materials behavior subjected to complex loadings. Stresses applied in biaxial experiments may constitute the stresses that materials experience during their service life. Test devices attached to the universal testing machine are beginning to be increasingly more widespread due primarily to reduced acquisition, operation and maintenance costs and the possibility to be customized according to specific needs required by type of experiments, to the detriment of freestanding machines. Of these, the most representative devices are pantograph type and sliding type, each having advantages and disadvantages. The present study examines two types of mechanisms that are used to test biaxial cruciform specimens in order to evaluate them in terms of achieving the conditions imposed by planar biaxial tensile testing.
Authors: Ovidiu Antonescu, Ioana Popescu, Păun Antonescu
Abstract: By the composing of the rotation movements with the concurrent instantaneous axes in a point, a rotation movement with the instantaneous axis passing through that point is obtained. The resultant instantaneous angular velocity is sum of the component angular velocity. As examples of the mechanical systems in which appear the concurrent rotation movements are: the pivot bearings of the radial-axial with balls type, the ball radial bearings and the planetary mechanisms with bevel gears which are used both as differential to automotives and as orientation mechanisms (wrist) on the industrial robots.
Authors: Virgil Atanasiu, Cezar Oprişan, Dumitru Leohchi
Abstract: This study presents a dynamic model of helical gears for analyzing the effect of pinion-shaft flexibility on the dynamic behavior of helical gears. In the analysis, the time-varying mesh stiffness is determined in relation with the geometry of the gear pair and incorporates the deflection of the pinion–shaft. A comparison analysis is presented for the dynamic transmission error response of gear pairs supported with a rigid and a flexible shaft system. The results show that the pinion-shaft deflection must be included in the dynamic analysis since they can strongly affect the dynamic characteristics of helical gear pairs.
Authors: Carmen Bujoreanu, Cristel Stirbu
Abstract: To realize an efficient car suspension control (for instance in technical inspection) it is important to use easy measurable variables. This is the reason for developing optimization techniques in order to simplify and improve the engineering design process. The paper presents an optimization process of a torsion bar spring included in the car suspension involving the following steps: modeling and analyzing the torsion bar spring behaviour, definition of the optimization objective and the specifications for the proposed solution choosing an appropriate methodology to satisfy the design objectives. It has been used a Min-Max optimization method to highlight the vibration response (in terms of RMS) of the system. CAD analysis and MatLAB optimization are performed on the car suspension elastic element and the obtained results provide an optimum vibrational response and constructive design. This combination of these analyses can be considered an efficient tool in order to ensure the driver and passengers comfort according to the standards.
Authors: Marin Chirazi, Emil Budescu, Eugen Merticaru
Abstract: The paper deals with the kinematical approach of the trajectory of movement of an academic rowing skiff with a view to determine a given racing speed of the boat. It uses inverse kinematics since this method allows obtaining analytical calculus formulas for the movement of paddles in their two moments of motion: active and passive strokes. Movement of the paddles while following an arc-shaped trajectory outlining a sphere-like quadrilateral requires different values of amplitude of angular displacement of the paddles according both to anthropometrical values of the athlete and to his physical and technical training. The numerical application is made for several values of these angles which define the arcs of the circle for active and passive curves and for the moments between the two strokes (angle of the paddle while slicing in and out the water). These amplitudes of angular displacement are being considered, from the point of view of the horizontal component, equal to the speed of the skiff while imposing the linear speed of the paddle, and they would help determining movement frequencies of the paddle while following the sphere-like quadrilateral trajectory.
Authors: Daniela Ciobanu, Codruta Jaliu, Radu Saulescu
Abstract: The use of renewable energy sources represents a continuous concern for the researchers around the world. The main source of renewable energy, the sun can be used for producing hot water / heating or electric energy, by means of solar collectors. The concentrating solar collectors contain tracking systems for orientation on one or two axes. The tracking system for the elevation motion has to ensure a reduced angular stroke. The mechanism that is usually included in the system structure is of linkage type, being driven by a linear actuator. The mechanism has the advantages of low complexity and reduced cost. In the case of diurnal motion, the angular stroke is larger, being usually obtained with gears or chain drives. The actuation is achieved by motor-reducers with high transmission ratios and costs. In order to reduce the costs, mechanisms containing linkages driven by linear actuators are proposed in literature. These tracking systems have the disadvantage of large overall dimensions. To reduce this disadvantage, the paper proposes a new variant of chain tracking system driven by a linear actuator. Then the proposed tracking system is structurally optimized, process that generates 6 new variants of mechanisms. These solutions eliminate the problems created by the hyperstatical constraints and avoid blocking in case of assembling errors.
Authors: Bogdan Cristescu, Ana Cristescu, Laurenţia Andrei
Abstract: The paper resumes the traditional hypotheses for the noncircular mating centrodes design, based on the definition of i) the driving centrode geometry ii) the transmission ratio variation and iii) the rotational motion of the driven centrode. Each procedure is transferred within the gear theory and developed considering both specific gear data, such as gear modulus, gear number of teeth and gear number of rotations during a rotational period. Original codes are developed in Php amd MyQSL to illustrate gears conjugate pitch curves geometry and their kinematics for external rolling.
Authors: Cezar Duca, Florentin Buium
Abstract: The paper deals with singularity problem of the closed-loop planar mechanisms. This problem is approached in addition with the force transmission quality in mechanism and mechanism self-locking. Another characteristic of this approach consist in the fact that it is based on the structural group notion. Taking into account its frequent usage in practice in the paper were treated only RRR, RRT and RTR structural groups.
Authors: Cezar Duca, Florentin Buium
Abstract: This paper continues some ideas accepted in scientific literature or enunciates by us in previous papers. As title indicates, we treated the case of 0/3/3 structural group with revolute joints, and application of this group in mechanisms. Three different proposals were done and discussed for the forces transmission indices. Finally an application was shown for a mechanism used in a leather ready-made industry.

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