Applied Mechanics and Materials Vol. 823

Abstract: The paper presents aspects regarding the virtual modeling, detailed design and FEM analysis of a testing device, to be used to fix small pieces in tribological tests. First there are presented some aspects of the device virtual modeling and drafting, using CATIA software. Then are defined the geometrical and kinematical restrictions between the parts. Finally, there are presented some aspects about the Finite Element Analysis and the results of this, using ANSYS software. In the final part of the paper, there are presented the conclusions of the simulation.

Abstract: The work deals with the optimal design of a single-axis solar tracker, which is used to adjust the daily position of a photovoltaic system in order to capture as much as possible solar radiation. The two main components of the solar tracker (the mechanical device and the control system) have been coupled (integrated) in the concurrent engineering concept. For assuring high stability and robustness, the control system is a cascaded two-loop employing LPF (Low-Pass Filter) controllers. The controlled parameter in the main (external) loop is the daily angle of the photovoltaic platform, while in the secondary (internal) loop the linear velocity in the driving actuator is monitored. The mono-objective optimization problem is described in the following way: to minimize the difference between the imposed and current daily angle (thus preserving a high energetic efficiency of the tracking system), considering the controllers’ gains as independent design parameters.

Abstract: The helical trough of a vibratory elevator induces, by its helical vibratory motion, a complex behavior to the transported parts. The paper analyses the displacement of a singular plate material particle on the cylindrical helix of a vibratory elevator, by decomposing the particle motion on slide and jump phases, dependent on the functional specific features of the vibratory equipment. A computer model of the particle motion was developed to study the theoretical average transportation velocity on the helical vibrating surface.

Abstract: The most outstanding parameter that governs the fatigue crack growth under tensile stresses field is the stress intensity factor, mode I, K_I. This is a sufficient parameter to describe the whole stress field at the crack tip. An accurate stress intensity factor K_I evolution was worked out taking into account the position of the crack centre depth, and also, the residual stresses that act on the surface of the tooth, tensions that are linearly decreasing with the depth in the contact zone. On the other hand, the parameter that governs the crack fatigue growth in the case of compression stresses field is the stress intensity factor mode II, K_II. This paper also presents the K_II variation along pitch line with respect to the Hertzian contact stresses, the residual stresses and the crack centre depth of an initial crack in the sub-surface of the pinion tooth, having different inclination angle α. As result of this study, some particular factors favorable to the propagation of the fatigue cracks towards the surface of the gear tooth were identified. The availability of a master curve for a particular material relating fatigue crack growth rate and range of stress intensity factor enables a designer to predict growth rates for any cracked body, and it is not limited to situations similar to those pertaining to the cracked stressed specimen used to generate the original data.

Abstract: The values of the stress intensity factor (SIF) K_I are almost always negative in the substrate of the gear teeth, due to the compressive stresses field. The more negative values are higher, respectively, the positive values are lower, the crack faces are more compressed, so the probability of crack propagation after the mode I is lower. Thus, the analysis of the factors leading to the minimum K_I values may reveal the conditions that favor the fatigue crack propagation by opening mode. Instead, SIF K_II is determinant in the growth rate of the fatigue crack by mode II, in terms of compressive stresses field. Thus, the more K_II is higher, the propagation speed is higher, so an analysis of the factors that lead to its maximum value is very useful. The equivalent stress intensity factor K_eq corresponds to a mixed-mode of loading and take into account the simultaneous influence of both stress intensity factors K_I and K_II. The variation of this factor can be used as a parameter of the modified Paris law, in order to study the propagation of the fatigue cracks in the case of mixed-mode loading of contact area between teeth flanks. SIFs variations were analyzed according to the state of stresses, position on the pitch line between the gear teeth flanks, position and angle of an initial crack in the gear tooth substrate, residual tensions etc.

Abstract: As is known, the gearing seems the principal excitation source into the components of the power transmission. The momentary movements of pinion driving gear and driven gear are represented by six liberty degrees, three translations and three rotations. The fluctuations of the conveyance error and of the gearing rigidity are the principal causes of the excitations associated to this one. For the conveyance error, it is necessary to tell the consequences of the elastic deformations from the kinematic consequences associated to the gearing of the non-mating profiles. In this paper is presented the simulation of the conveyance error associated to the eccentricity faults. In order to obtain the dynamic response it is suggested the using of the integral Laplace’s transform.

Abstract: This paper investigates the possibility to individually balance the specific shaking forces and shaking moment of the slider-crank mechanism. The most common mean of balancing the slider crank mechanism is to use a counter mass. This solution is applied for almost every slider-crank mechanism used in commercial mechanical devices. However the nature of the mechanism does not allow a perfect balancing in such a way. The different nature of motions that govern the piston displacement and crank rotation imply that a counter mass can only statically balance the mechanism. An ideal dynamic balancing cannot be achieved this way. Therefore in this paper the excitations that act on the mechanism are split by the nature of motion that generates them and balanced accordingly. Two motions are defined, respectively the motion of the piston and the motion of the crank. The inertia force associated with the crank motion is balanced by building a dynamically equivalent system around the axis of the crankshaft while the excitation associated with the motion of the piston is balanced with a progressive spring with two rates.

Abstract: This paper presents new formulations on the higher order motion energies that are applied in the dynamic study of multibody mechanical systems in keeping with the researches of the main author. The analysis performed in this paper highlights the importance of motion energies of higher order in the study of dynamic behavior of fast moving mechanical systems, as well as in transient phase of motion. In these situations, are developed higher order time variations of the linear and angular accelerations. As a result, in the final part of this paper is presented an application that emphasizes this essential dynamic aspect regarding the higher order acceleration energies.

Abstract: Using the main author's researches on the energies of acceleration and higher order equations of motion, this paper is devoted to new formulations in analytical dynamics of mechanical multibody systems (MBS). Integral parts of these systems are the mechanical robot structures, serial, parallel or mobile on which an application will be presented in order to highlight the importance of the differential motion equations in dynamics behavior. When the components of multibody mechanical systems or in its entirety presents rapid movements or is in transitory motion, are developed higher order variations in respect to time of linear and angular accelerations. According to research of the main author, they are integrated into higher order energies and these in differential equations of motion in higher order, which will lead to variations in time of generalized forces which dominate these types of mechanical systems. The establishing of these differential equations of motion, it is based on a generalization of a principle of analytical differential mechanics, known as the D`Alembert – Lagrange Principle.