Volume 45, Nº 5 (2016)
- Ano: 2016
- Artigos: 14
- URL: https://journals.rcsi.science/1052-6188/issue/view/12120
Mechanics of Machines
Kinematics of deployment of petal-type large space antenna reflectors with axisymmetric petal packaging
Resumo
This paper is concerned with the kinematics of the deployment of petal-type large space antenna reflectors with axisymmetric petal packaging. The classification and technical design solutions for petal deployment mechanisms and the results of their comparative analysis have been presented.
Infinitesimal displacement analysis of a parallel manipulator with circular guide via the differentiation of constraint equations
Resumo
This paper considers several subproblems associated with solving the forward and inverse position and speed problems and defining singular configurations for a parallel robot with six degrees of freedom and six kinematic chains that move along a circular guide (rotopod). The solution of these subproblems is necessary for analyzing the topological features of the parallel robot and employing the results of such analysis in control algorithms design.
Determination of the degree of mobility and solution of the direct kinematic problem for an analogue of a Delta robot
Resumo
A manipulator with three degrees of freedom similar to a Delta robot has been considered. The mechanism degree of mobility has been analyzed and, in the general case, the mechanism has negative mobility. Structural diagram of the mechanism with three degrees of freedom similar to the original one is constructed for solving the direct and inverse kinematic problems. A method for determining mobility based on the study of coupling equations of the mechanism has been proposed. The method is applied to the considered spatial mechanism, an analogue of a Delta robot. The direct kinematic problem has been solved.
Design of drives with double-reduction wave gears for servosystems
Resumo
The design technique of kinematic diagrams of reducers with double-reduction wave gears as the output stage of electromechanical drive. The application of double-reduction wave gear in the electromechanical drive can significantly reduce its dimension specifications and mass while decreasing the load capacity and efficiency.
On the problem of the excitation of self-oscillations in relaxation friction
Resumo
With regard to the problem of decreasing the vibration activity of devices that perform the translational motion of the working body along the pathway, new results have been obtained that determine the threshold speed value; the friction self-oscillations occur lower than this value. It has been established that this value increases upon a decrease in the dissipative characteristics of a drive. The dual character of the influence of the high-frequency disturbance, which leads to the positive effect due to the vibration linearization of the dry friction forces, but simultaneously decreases the realized dissipation level of a drive, has been studied. The optimization of the high-frequency excitation parameters has been performed based on an analysis of the combined influence of these factors. The main conclusions have been proved based on the results of computer modeling.
Realibility, Strength, and Wear Resistance of Machines and Structures
Features of fatigue crack development in cast steel parts of railroad structures
Resumo
The paper presents the results of an experimental study on the features of fatigue crack development in 20GFL grade low-alloy steel of a freight car bolster with simulation of the operating process of loading. The experiment results are compared with calculations using the fatigue failure diagram for this steel.
Estimation of the probability of mechanical systems breakdown by technical state modeling
Resumo
This study considers the general model of estimating changes in technical state of mechanical systems caused by external action. This model makes it possible to estimate their effect on the probability of breakdowns. The considered examples include the destruction probabilities for crank rods of the opposite compressor to be simultaneously affected by cyclical loading and wear.
Reliability of the aboveground site of an oil and gas pipeline at transverse-longitudinal bending
Resumo
The article provides a solution to the problem of determining the probability of the nondestruction of the beam site of an oil and gas pipeline with axial compressive force when the pressure, diameter, wall thickness, span length, the coefficient of linear expansion, temperature difference, Poisson’s ratio, and ultimate strength are distributed normally. According to these data, parameters are established under which the emergency failures of oil and gas pipelines are reduced and their specification level of reliability is provided.
Numerical simulation of carrying capacity of the high-pressure metal composite vessel
Resumo
This paper considers the issue of the numerical simulation of stress–strain state and the destruction of the composite vessel with a metal liner under gradually increasing pressure. The provided solution algorithm is based on the continuum of damage mechanics simulation that relates to the initiation of damage and the accumulation and degradation of the mechanical properties of material. The calculation results are compared with the actual experiment data.
Vibration strength of structures based on the theory of cracking and fatigue curves
Resumo
The algorithm for calculating a fatigue crack formed in force parts of structures under the harmonic vibration load has been presented. The source data for calculating an unknown quantity are fatigue curves in the material and the assumed linearity of the first section of the kinetic diagram of the fatigue fracture. All of the necessary parameters for describing the law of crack propagation in the form proposed by Paris are determined by the characteristics of the fatigue curve. This approach shows that the fracture of the thin-walled force parts of structures with a thickness of less than 2 mm (the size of a fatigue crack for which the fracture of samples is tested to develop the fatigue curve) occurs at a smaller number of cycles than that shown in the fatigue curve for the same stress amplitude.
Development of method for evaluating performance of worm gears via analysis of their tribological characteristics
Resumo
The occurrence of self-excited frictional oscillations in a worm gear and their interrelation with the performance characteristics of the gear are considered. A method for accelerated testing of worm gears is proposed based on the obtained relations. Results of the tests carried out using various lubricants are presented.
New Technologies in Mechanical Engineering
Increase in the filtration capacity of the bottomhole zone in the reservoir by wave impact for well stimulation
Resumo
The possibility of well stimulation via wave impact has been studied. The effect of an increase in the filtration capacity of the bottomhole zone in a reservoir observed during treatment with high-frequency waves has been surveyed.
Modeling the structure formation during hot deforming the billets of the parts of gas-turbine engines made of heat-resistant nickel alloy
Resumo
The results of finite-element and physical modeling of deformation heating and structure formation during high-temperature isothermal upset of a cylindrical billet according to various modes (continuous and fractional deformation) have been presented. The results of numerical modeling, which agree with the experimental modeling data, showed that, in order to minimize the deformation heating and formation of a homogeneous ultrafine-grain structure in bulk billets made of heat-resistant alloys, it is purposeful to perform the deformation fractionally (with a single degree no larger than 30–50%), which allows for the deformation rate and performance of post-deformation annealing. The formation of an ultrafine-grain structure in the billets made of nickel alloys (for example, EP742U) guarantees an increase in the quality of ready wares.
Experimental Mechanics, Diagnostics, and Testing
Structural design and testing of composite wing high-lift device
Resumo
A problem for designing aviation structures made of sandwich-like polymer composite materials has been examined based on the example of a typical device for mechanizing a wing-spoiler. The spoiler’s loading pattern is chosen according to topological optimization. A way to determine the orientation, number, and proper order of layers laying has been examined as a problem of discrete optimization by using different algorithms. The peculiarities of layered structure simulation have been discussed. Tests results for spoiler have been presented and they verify the design and technological solutions.