Abstract
Until now, planetary rotary hydraulic machines with floating planetary gears were rarely produced and remained poorly studied. One of the main problems was the lack of a simple and ...affordable method for geometric design of non-circular gear rims of such machines. The article discusses an engineering method for profiling non-circular gear rims of volumetric planetary rotary hydraulic machines. The proposed method begins with the choice of the geometric parameters of the round-link planetary mechanism - the prototype of the designed hydraulic machine. Next, the number of waves of the sun gears and the form of the cyclic function characterizing the paths of the planetary gear center in the coordinates associated with the sun gear and the epicycle are selected. The preliminary calculation of the angle of rotation of the planetary gear and the polar coordinates of its center on the path relative to the given sun gear in the variety of the planetary gear positions is performed at the next stage. In this case, the positions of the planetary gear relative to the one of the sun gears correspond to its rolling along the calculated centroid of this gear at a constant angular velocity of the imaginary carrier. Next, the difference between the obtained angles of rotation of the planetary gear is calculated in the coordinates associated with the imaginary carrier. This difference is halved and distributed as a correction between the rotation angles of the planetary gear relative to the sun gear and the epicycle. In conclusion, the profile of the rim of each non-circular sun gear is obtained graphically as an envelope of the family of profile curves of the planetary gear in a variety of its positions. The proposed method provides an accurate solution to the problem and is available for the designers of any machine-building enterprise.
In this paper, we compare two approaches to describing the rate dependence of the strength of materials under conditions of dynamic loading with a constant strain rate. The first is based on a ...structural model of a brittle continuous medium with defects, which makes it possible to derive a semiempirical normalization relation to describe the rate dependence of the strength of a wide class of materials in a single normalized space. The second is based on the concept of incubation time of destruction, which is a strength parameter that characterizes the sensitivity of a material to the intensity and form of the loading impact. The interrelation and distinctive features of these two approaches are studied, as well as the rate dependences of strength for some materials are compared by modeling.
The paper proposes an incremental relaxation plasticity (IRP) model for predicting possible instabilities and overall behavior of flow curves under dynamic loads. Compared to its original ...non-incremental version, the IRP model allows one to predict the behavior of stress-strain curves over a longer time after the start of yielding and to more accurately describe their instabilities such as sharp yield points (yield drops) and further nonmonotonic or oscillatory effects. The efficiency of the IRP model is demonstrated by comparing its predictions with those of the original non-incremental version and of the widely known Johnson–Cook model on the example of experimental flow curves for dual-phase high-strength steel DP800 and aluminum alloy 2519A. The major feature of the proposed IRP model is that its parameters are invariant with the loading history and strain rate of a material and are related only to the evolution of its defect structure on the micro- and mesoscales. With such a set of IRP model parameters, one can obtain a variety of flow curves of the same material at widely varied strain rates.
Ultrasonically assisted drilling (UAD) is a non-traditional machining process that employs the vibration of a cutting tool. It offers a better alternative and solution to the challenges of drilling ...marble using conventional drilling (CD) methods. Machining-induced damage in marble results in the rejection of parts. A significant force reduction is achieved when applying UAD in marble, therefore eliminating large craters created at the exit of the hole in CD, caused by the high force generated. This work presents original experimental results for both drilling techniques, and suggests an analytical model for UAD based on a combination of a contact-problem solution and an incubation-time approach. In the modelling, the problem of fracture at different scales was considered, solved by employing a principle of equal power. The predictions of the presented theoretical model for UAD were validated by comparison with the experimental data, demonstrating a good qualitative agreement.
The penetration of a liquid jet into a space filled with another liquid for the case of large difference in density between these liquids is examined as applied to the fragmentation and mixing of ...jets during various accident scenarios at nuclear power plants (discharge of corium melt into water or water into a volume filled with liquid lead). The hydrodynamic equations for several immiscible liquids with sharp interfaces were solved using the Volume of Fluid (VOF) method. Mathematical models of multiphase flows, implemented numerically in the OpenFOAM open source package, are presented. A series of verification and research calculations was performed in a two-dimensional (plane) approximation, and the obtained results were compared with the published data. The results of calculation of the penetration of a Wood’s metal melt jet into a deep water-filled vessel, performed using this approach, revealed successive stages in the evolution of a fragmenting jet. A good qualitative and quantitative agreement of the predictions with the published results of the calculation of this process by the ANSYS Fluent code were attained. The regularities of mixing of a water jet discharged into a volume filled with initially stagnant liquid (molten) lead are studied. It has been demonstrated that the fragmentation of the water jet occurs almost immediately after it enters the liquid lead in this case. The effect of the grid cell size on the characteristics of phase mixing was examined. The predicted characteristic sizes of the formed fragments, their dispersed composition, and the interfacial surface area during mixing are presented. Nomograms of the size distribution for the fragments formed during the jet breakup were plotted for both studied problems. It is shown that the melt fragments formed in this process are much smaller than the minimum limit size of melt droplets freely falling in water.
Test results are presented for an additive material prepared of acrylonitrile-butadiene-styrene on a 3D printer. Dynamic tension experiments have been carried out using a tower-type drop hammer with ...an accelerator. Data obtained from different specimens demonstrate that high-strain-rate tensile experiments are feasible if the working part of the specimen is decreased. A theoretical analysis of test data using the incubation time criterion has been performed, and it has been found that analytical results are in good agreement with experimental data.
Planetary rotary hydraulic machines (PRHM) with wavelike sun wheels and floating satellite wheels have high technical characteristics but they are understudied. The article is devoted to the ...estimation of energy efficiency of PRHM at the stage of their projecting. Calculated formulas for the pump and hydraulic engine are offered. The comparative estimation of schemes with the numbers of waves M×N: 2×2; 3×3; 4×4; 2×4; 4×6, has shown efficiency values close to each other a little bit more than 0.9. The reserve for efficiency upgrading for the considered hydraulic machines is the use of the teeth with half-round convex-concave side surfaces.
We have studied the fracture problem of layered media under combined dynamic loading. The effect of background harmonic vibrations on the amplitude of the main force pulse is analyzed. The features ...of fracture from such a combined action are demonstrated using a simple 2D model (a circular membrane on an elastic base). As the condition of adhesive layer rupture, the incubation time criterion is used. It is shown that the threshold amplitude of breaking action can be substantially reduced by correctly choosing the excitation frequency even for low intensities of the background field.
Experimental and theoretical data for the strength performance of 1230 aluminum alloy under tension in the quasi-static and dynamic ranges of loading parameters are presented. Using the structural ...temporal approach and the sign-perturbed sums algorithm, the feasibility of raising the strain rate of a specimen by decreasing its geometrical size has been estimated.
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