Բանբեր ՀԱՊՀ - Մեխանիկա, մեքենագիտություն, մեքենաշինություն

THE STRESS STRAIN STATE IN THE PROCESS OF DEFORMABLE INDENTER PENETRATION INTO THE ELECTROCONDUCTIVE HALF SPACE IN THE PRESENCE OF DISCHARGE CURRENT

2019-03-22T15:51:16+00:00

The main goal of this work is to study the influence of the discharge current on the characteristic values of penetration. As it has turned out, LRC circuit parameters, the impact velocity, the type of discharge current significantly influence the penetration. However, as experiments and numerical calculations have shown, an important role plays the distance between the target and the plate . It is known that the electron plastic effect depends on the current value, direction of , as well as the current exposure time. It follows that the distance of the plate from the target also influences the electron plastic effect, which occurs in the
penetrating indenter on the segment between the contact surface of the deformed indenter with the crater and the plate, with a crater. Because the length of the segment affects the closed LRC circuit time, and which, in its turn, affects the time of discharge current on the plastic properties of the indenter, as well as the duration of the Ampere force as a pinch effect becomes essential. From a practical point of view, it is important to study the problem of the indenter (jump) rebound from the crater. For this purpose, approximate estimates were carried out in [1] for the deformable indenter. The (jump) rebound of the indenter may occur due to the fact that after stopping the indenter in a half space or in the case when the depth of penetration is less than the thickness of the target, in the target, due to the elastic, (stored) accumulated in the indenter and the target stresses, the reverse motion of the indenter takes place. Thus, if the friction forces between the indenter and the target are less critical, a (jump) rebound of the indenter from the crater occurs. This phenomenon was observed at the experiments, when the barrier was shot in the presence of the current. The blunting of the indenter and the pressing force in the target create favorable conditions for rebound.

ANALYSIS OF SINGULARITIES AT THE CENTER OF HETEROGENEOUS HONEYCOMB CELL UNDER ANTIPLANE DEFORMATION

2019-03-22T15:56:06+00:00

In this paper, we discuss the presence or absence of stress concentration at the center of two kinds of heterogeneously dissimilar honeycomb cells under antiplane deformation. Determining the presence of stress concentration is necessary to determine the criteria for the destruction of structural elements. In the first case, a continuous two-compartment cell is considered, for which the boundary conditions have periodically repeating characteristics. In the second case, the heterogeneous cell is assumed to be discontinuous, with a cutout of one of its quarters, for which the periodic nature of the boundary conditions is violated. Thus, the task of investigating heterogeneous cells for the presence or absence of stress concentration at their center is reduced to the comparison of stress-strain states in the case of antiplane deformation of two differently dissimilar honeycomb cells: honeycomb cells with significantly and slightly different physicomechanical characteristics, for which, as it turns out, the picture of the stress state near the center is radically different. The study was carried out using modern methods and tools of computational mathematics and programming.

СДВИГОВЫЕ КОЛЕБАНИЯ В СОСТАВНОМ ПЬЕЗОЭЛЕКТРИЧЕСКОМ ПРОСТРАНСТВЕ

2019-03-22T16:05:37+00:00

It is known that the issues of studying patterns and identifying features of disturbances in elastic dielectric media during the interaction of elastic and electroelastic fields are of scientific interest, therefore, they are among the urgent problems of mechanics of solid deformable bodies. Studies of the processes of vibration and propagation of electro-elastic waves in an inhomogeneous medium with a piezoelectric effect are closely related to the development of
electroacoustics, piezotechnics and measuring instruments. Obviously, the possibilities of modern technology for creating constructively heterogeneous materials for engineering practice have increased. The results of the problem of the propagation of shear vibrations in a composite piezoelectric space considered in the present paper can be used for studying applicable problems of propagation of electroelastic localized and volume waves. A linear mechanical
oscillation source acts in the composite piezoelectric space. The inhomogeneity of the medium with a 6mm symmetry, the piezoelectric effect and the presence of a power source lead to significant changes in the wave field. The coherence of the physical fields is due to the propagation of surface (localized) waves with particle displacements in the direction of the symmetry of the crystal. The problem of the interaction of different fields of physical origin in solids is interesting
from the point of view of continuum mechanics and mathematical physics, and of course, it is very important while designing engineering-physical devices and studying the principles of operation of new modern acoustoelectric devices. The paper studies the linear interaction of the electric and mechanical fields in the contact of two piezoelectric half-spaces, under the action of a linear source of steady-state mechanical perturbations in one of the half-spaces, and an electroelastic wave field is constructed in a composite piezoelectric space.

КОМПЬЮТЕРНОЕ МОДЕЛИРОВАНИЕ ПРОЦЕССА ОБРАЗОВАНИЯ ШЕЙКИ ПРИ РАСТЯЖЕНИИ КРУГЛОГО ОБРАЗЦА

2019-03-22T16:14:47+00:00

The tensile test of a plastic deformed circular cross section sample is one of the most important method for determining the mechanical properties of a material. At small plasticdeformations, the stress state of the sample is uniaxial. With an increase of plastic deformations, a neck is formed in the sample, where there is quite complex concentration of stresses (three dimensional unhomogenious stress state), due to which the initial microporosity in the material increases, additional pores are formed around nonmetallic inclusions of different origin, which, being connected with each other, make cracks, and the sample is
destroyed. Theoretical and experimental data known in literature have been used in the study, taking into account the porosity of the material and the change in the stress state in the neck (from uniaxial to triaxial), the values of the gradual change of the porosity of the material before and after the formation of the neck and at various points of its smallest cross section have been determined. While solving these problems, assumptions were admitted the accuracy of which can be estimated by using numerical methods. The tension test of a metal sample was modeled in the ABAQUS software environment. The problem was solved for different values of displacement from both ends of the sample. Data on the stress-strain state were obtained, and the analysis of these data was carried out. The finite element mesh of the sample in ABAQUS was obtained, using the tetrahedral CAX4R and trihedral CAX3 elements. The characteristics of elasticity (Young's modulus, Poisson's ratio, material density) and plasticity at different degrees of deformation (data of the deformation graph) of the material were chosen.

К ПРОЕКТИРОВАНИЮ МНОГОЦЕЛЕВЫХ УРАВНОВЕШЕННЫХ УСТРОЙСТВ АССИСТИРОВАНИЯ ОПОРНО-ДВИГАТЕЛЬНОЙ СИСТЕМЫ ЧЕЛОВЕКА

2019-03-22T16:25:50+00:00

For the development of multi-functional assistive devices, a new methodological approach is proposed based on the principle of their parallel design. Traditionally, such devices are created by the human musculoskeletal system functions, assisting theserial solution of the task: the leg balancing during walking, the body balancing during sit-to-stand; and their functional abilities are extended by overlaying the developed technical solutions. The new approach provides the device multi-functionality at its conceptual design stage byincreasing themobility degrees and assumes the use of the same elements for realizingvarious functions. With this, the number of elements is reduced and, as a result, new advantages are gained, such as mobility, the opportunity of balancing a greater number of the humanbody segments, at the same time assisting the balancing of the biomechanical system of the body, and the assisting device in general. The proposed approach illustrated on a specific example of a new assistive device development, provides a human and device biomechanical system total static balancing during a human`s walking and sitting. The achieved main advantages of the device are its universality, compactness, adjustability and comfort in comparison with the known analogues. The designed device can be used both for assisting the human musculoskeletal system, and physiotherapy. At the same time, the device also provides the dosing of the loads and angular displacement ranges, hence, greater efficiency in human physiotherapy. The proposed approach to the human musculoskeletal system assisting multi-purpose balanced device design is quite universal and can be used for designing not only assisting, but also for other similar - purpose portable rehabilitation devices.

STUDY OF STRESSES IN MATERIALS WITH REGULAR MICROSTRUCTURE FOR THEIR APPLICATION IN THE DESIGN OF POLYGRAPHIC CUTTING MACHINES

2019-03-22T16:32:50+00:00

Modern polygraphic equipment is required to be designed with minimum weight and dimensional parameters. The optimal modes of their operations are also very important. These requirements can be met by using cellular materials with regular microstructure, which are manufactured using special technologies. To design the links of the mechanisms of polygraphic equipment from new materials, first it s necessary to study the strength properties of cellular materials. This exploration will show how the stress will be distributed in the microstructure of the material. It is also important to find the points in the unit cell of the microstructure, where stresses will get their maximum values. This paper presents the influence of the geometrical parameters of a unit cell on the stress distribution inside the material of a regular microstructure. Studies have been carried out by modeling the stress state of a unit cell using the numerical method. A numerical method is proposed for the estimation of the stress concentration factors (SCF) on the cell wall junctions of the cellular structure. The SCF was
defined by multiplying the nominal stress components applied to the sides of the unit cell to the stress components at the filleted cell wall junction. The use of materials with a cellular regular microstructure in the design of polygraphic equipment will save material resources. In addition, this will open up new opportunities to fill the cells of the microstructure with piezoactive materials, which are a source of high-frequency vibrations that improve the performance of machines.

ЗАВИСИМОСТЬ ИЗНОСА РЕЖУЩЕЙ ПЛАСТИНЫ И ШЕРОХОВАТОСТИ ОБРАБОТАННОЙ ПОЕРХНОСТИ ОТ РЕЖИМОВ РЕЗАНИЯ ПРИ ТОНКОЛЕЗВИЙНОЙ ОБРАБОТКЕ ЦВЕТНЫХ СПЛАВОВ

2019-03-22T16:42:39+00:00

The dependence of roughness of the processed surface and the wear on the rear face on the optimal cutting conditions at thin-blade processing of aluminum and copper alloys with corundum cutting plates is given. The possibilities of thin - face milling of non-ferrous metals and alloys in terms of the quality of processing are revealed if we use cutting plates that are pre-oriented along the crystallographic axes, taking into account their unique properties. Experiments show that with an increase in the cutting speed, the height of microscopic irregularities decreases. It is characteristic that at low cutting speeds, this intensity of reduction is more obvious. A further increase in the speed does not lead to significant changes in Ra. Thus, the cutting speed has a great influence on the surface roughness. With the increase of v, plastic deformation decreases, therefore the height of microscopic irregularities Ra decreases. When processing low-plastic metals with high abrasion, surface microgeometry is determined by the conditions of friction and the distortion of the blade profile as they wear out. The feed also has a certain effect on the formation of surface microgeometry. The feed rate determines the shape and height of the residual scallops. With an increase in the thickness of the cutting shavings, the volume of the cutting layer will increase, the working length of the contact of the shavings with the front surface of the tool increases. When reducing the deformation of the layer being cut, the cutting force increases. Consequently, for these reasons, an increase in the feed rate leads to a deterioration of the surface microgeometry inherent in this type of machining. It is proved that the roughness of the processed surface at thin- balde machining of non-ferrous alloys with corundum cutting tools is within Ra = 0.32... 0.08 mkm, similarly to diamond. The wear on the rear face (h3 = 0.1 mm) when processing the above materials is 250...280 km, without the use of LCTM.

О ВОЗМОЖНОСТИ ПОВЫШЕНИЯ ПРОЧНОСТИ И ПЛАСТИЧНОСТИ ТИТАНОВОЙ ФОЛЬГИ С УЛЬТРАЗВУКОВЫМ УПРОЧНЕНИЕМ ЕЕ ПОВЕРХНОСТЕЙ

2019-03-22T16:56:56+00:00

Based on the analysis of the literatary sources and experimental data, it is shown that titanium has specific physical and chemical properties, in particular high specific strength and ductility, low specific weight, corrosion resistance in many corrosive environments, the ability not to be magnetized, high heat resistance and low thermal conductivity, which are maintained in a wide temperature range, including cryogenic temperatures. The main consumer of titanium products are the military and aviation industries. Titanium is also widely used in shipbuilding, it is extremely popular in medicine. Currently, it is widely used in engineering, automotive, oil and gas industry, nuclear power, jewelry, construction, for the manufacture of light sports equipment, and harmless titanium dioxide is used as a pigment in paints, pharmaceuticals and pharmaceuticals, food industry products and other products. Therefore, at present, the demand
for titanium products is growing from year to year, and the world production of titanium sponge is increasing annually by 5 ... 7%. Based on the study and analysis of the results of well-known research on the development of technology for producing titanium billets, it is found that the possibilities of improving their physico-mechanical properties are not exhausted and conducting new research in this direction is an urgent task. In the paper, the possibility of improving the physicomechanical properties of titanium foil by additional bilateral hardening of its surfaces, an indenter oscillating with an ultrasonic frequency is substantiated. Schemes of devices for ultrasonic hardening of thin-walled machine parts have been developed.