Mechanics and Advanced Technologies

Simulation of the effect of multi-particle temperature on Al6061 coating porosity based on Coupled Eulerian-Lagrangian (CEL) method

2024-05-15T05:16:17+03:00

Cold spray is a solid-state deposition technology widely used in additive manufacturing. The particles temperature is mostly used to adjust the porosity of the coating. This article uses Pyhon script to model the multi-particle model; then the multi-particle model is nested in the CEL deposition model to simulate the actual cold spray multi-particle deposition process; The CEL method has the characteristics of high accuracy and robustness and was selected as the simulation method for the multi-particle deposition model. The porosity of the coating is expressed by studying the value of the EVF void area in the Euler domain. Multiple groups of samples were taken on the coating surface to calculate the porosity of each group, and the average value was finally taken as the porosity of the entire coating. Numerical results show that increasing the particle temperature can effectively reduce the porosity of the coating. The average porosity of the coating under the particles temperature conditions are 600 K: 5.08 %; 650 K: 4.02 %; 700 K: 3.58 %; deposition completed the inside of the coating appears to be compacted. The substrate temperature will affect the combination of the coating and the substrate. It is recommended that the temperature difference between the particles and the substrate should not be too large. The CEL method simulates the process of cold spray multi-particle deposition, which is an effective method to observe and predict the porosity of the coating, which is also unachievable by the SPH and ALE methods.

Technological support for processing pultruded glass fiber reinforced plastics

2024-06-20T22:58:13+03:00

The issues arising in production facilities engaged in processing composite materials are considered. Specifically, the solutions to problems encountered in the mechanical processing of composites are analyzed based on foreign scientific research and proprietary solutions employed in the enterprise. The main issues addressed include delamination of pultruded glass fiber reinforced plastics and the selection of proper cutting fluid for processing. A mathematical model for calculating cutting regimes has been developed. The mathematical model has been validated through experiments to determine the delamination coefficient with the calculated cutting regimes. The machining process of the workpiece has been simulated in the Ansys system using the Lagrangian approach with the finite element method. A computational experiment has been conducted using the PRIAM software. A methodology for designing final milling operations based on the criterion of limiting delamination and ensuring the specified surface roughness of laminated glass fiber reinforced composites has been developed. It has been established that with a constant cutting speed and depth of cut, and varying only the feed rate, delamination increases with increased feed rate. It has been found that with the same depth of cut and feed rate, and varying cutting speed, the surface quality is satisfactory, indicating a lower delamination coefficient. The mathematical model based on the conducted experiments has proven to be practical and effective for determining an approximate delamination coefficient. The obtained results have proven to be practical and are used in enterprises engaged in the mechanical processing of glass fiber reinforced plastics.

Comprehensive analysis of arc methods of 3D printing of metal products: assessment of the efficiency and prospects of using TIG as a heat source

2024-09-09T15:54:55+03:00

In recent years, additive technologies have become increasingly important for the production of parts with complex geometries, enabling the rapid and efficient creation of objects with different shapes and configurations in industrial sectors such as medicine, aerospace and construction. The focus of the study was the analysis of arc processes for additive manufacturing, particularly through non-consumable electrode welding in an inert gas environment (TIG) and its applications as a heat source.

Modern methods of 3D printing metal products, such as SLM (Selective Laser Melting), EBM (Electron Beam Melting), and LMD (Laser Metal Deposition), allow the production of parts with good quality indicators: accuracy, surface roughness, mechanical properties, and others. However, these methods are expensive due to the technological complexity of the equipment, and a weakness of these methods is their low productivity compared to arc methods.

The results presented in this article show that the productivity of arc methods in additive manufacturing is several times higher than that of SLM, EBM, and LMD, and arc methods are more cost-effective due to lower equipment costs and reduced energy consumption. The article presents the schemes of arc methods of additive manufacturing. One of the promising directions in the development of hybrid technology, namely the use of the TIG heat source for sintering metal powders, offers an effective way to reduce the cost of additive manufacturing by replacing the laser as a heat source, while allowing the continued use of various types of metal powders, reinforcing materials, and metal-ceramic blends.

Evaluation of Fused Deposition Modelling process parameters influence on the porosity of printed parts

2024-09-05T13:06:46+03:00

Fused Deposition Modelling (FDM) is an additive manufacturing technology that is rapidly gaining popularity due to its ability to produce complex shaped parts in a short time. However, parts produced by means of FDM have porosity that results from the printing process. The mechanical properties of printed parts depend on the FDM process parameters and porosity. This study investigates the effect of FDM process parameters on the porosity of FDM parts. The results of the study show that properly selected FDM process parameters can significantly minimize the percentage of part porosity. The effect of FDM process parameters on porosity was determined by analyzing nine process variables: layer height, extrusion temperature, printing speed, extrusion multiplier, bed temperature, infill pattern, deposited strand width, number of shells, number of solid top and bottom layers. The percentage of samples porosity was measured by means of the hydrostatic weighing method. Using the analysis of variance, statistically significant factors and their combinations affecting the percentage of parts porosity were determined. It was shown that the extrusion multiplier had the greatest influence on the percentage of parts porosity. A significant contribution to the formation of porosity was made by the infill pattern, layer heights, printing speed, number of shells, number of solid top and bottom layers and their interaction. A regression model has been developed that allows predicting the porosity of parts achieved by different combinations of FDM process parameters.

Simulation of resonant liquid sloshing in a tank with vertical baffles

2024-03-10T14:00:37+02:00

The material presents the results of numerical modeling of internal fluid flows geometry in tanks that are subject to fluctuations due to external force influences. Similar applied problems occur when transporting large volumes of liquid, for example, in tanker ships. Given the rather significant moving masses within the reservoirs (tanks), as a rule, there are shock pressures on the walls and internal structures of the guiding devices, which can cause their deformation and even destruction, which leads to serious emergency situations.
Numerous studies devoted to the determination of the force effects of liquid flows on the walls of tanks came to the conclusion that the presented phenomena are of a strongly nonlinear nature, depend not only on the amount of liquid and the directions of its movement within the tank, but also on the formation of velocity and pressure fields over time. The specified parameters are decisive in predicting possible resonance phenomena in tanks, which in turn can become the main factor in the design of means of damping or control of inertial fluid flows.
The proposed work is devoted to the mathematical modeling of the mentioned phenomena in tanks, as well as the analysis of the force effect of internal inertial flows, which cause the occurrence of shock pressures on internal structures. On the basis of the indicated research results, it is possible to propose rational from the point of view of damping the design of guide devices in the form of flat rigid baffles.

Functional reliability of means of fixation for complex pelvic fractures. Part 3. Experimental studies under cyclic loads

2024-07-31T12:58:08+03:00

Fixation of fragments of human pelvic bones by standard and new means of osteosynthesis, in addition to clinical indicators, should have sufficiently high mechanical characteristics. In particular, the “bone with a fracture - osteosynthesis system” system must be sufficiently strong, rigid and stable during long-term treatment, which may be accompanied by certain physiological loads. Today, in traumatology and orthopedics, two methods of fixation are used to fix complex fractures of the pelvic bones caused by high-velocity wounding projectiles: parallel insertion of spongy screws (osteosynthesis of the posterior pelvic ring) and stabilization with a rod apparatus of external fixation and fixation by means of reinforced with application of extramedullary reconstructive plate (osteosynthesis of the anterior pelvic ring). The anterior pelvis is stabilized more often because this technique is simpler, does not require much time and high qualification of the surgeon. However, this method of fixation does not provide sufficient stability of the connection of the pelvic ring bone fragments. This work is devoted to the study of the processes of occurrence and development of mutual displacements of fracture points of pelvic bones under the action of long-term cyclic loads. Experimental studies were carried out under the action of bending cyclic loads, which are close to physiological ones. Calculated creep deformations and irreversible displacements of fracture points. The stiffness characteristics of pelvic fracture fixation systems were studied.

Models and criteria of destruction of composite materials at the stage of macrocrack initiation

2024-08-09T21:44:13+03:00

The analysis was carried out and the limits of the use of modern damage models and criteria for the failure of composite materials (CM) at the stage of macrocrack initiation were established. The classification of CM and the main hypotheses and assumptions used in the development of the condition level are described. The main stage of the life cycle of a CM product is considered - the stage of nucleation and accumulation of scattered fractures at the micro and meso levels. The main principles of continuum damage mechanics, thermodynamics of irreversible processes and mechanics of a solid deformed body are used. The main mechanisms of microfailure of reinforced CM are described. It is shown that for them it is necessary to consider a set of phenomenological parameters that could assess the kinetics of the accumulation of diffused failures in the matrix, reinforcing fibers and the delamination between them. These complex processes in reinforced CMs require phenomenological modeling of damage in the form of tensor quantities with certain assumptions. Thus, the "mixture" hypothesis was widely used. It is shown that each component of the damage parameter is more expedient to determine from the hypothesis of the equivalence of specific energies. The method of conducting basic experiments to specify the regularities of damage accumulation in CM is detailed. A modified CM stiffness tensor is established, taking into account the degradation of the mechanical properties of the CM, regardless of the thermo-force parameters of the operating load. An analysis of modern criteria for the destruction of reinforced CMs and the limits of their use was carried out. The main directions of solving the problem of estimating the limit state of CM and the load-bearing elements made from them are shown.

Determination of metal crack resistance on half-size Charpy specimens at cryogenic temperatures

2024-06-20T15:57:43+03:00

The work consists in the manufacture of experimental equipment for fracture toughness tests at cryogenic temperatures in the range from -196 °Cto -80 °Cand the analysis of the efficiency of determining the reference temperature of a metal by the maker curve for static crack resistance in accordance with ASTM E 1921 and ASTM E399. Liquid nitrogen and its vapours were used to cool the samples to the required temperature. The temperature stability during sample loading was ensured within ±0.5°C around the required temperature. Pre-cracking of the samples was carried out at room temperature in accordance with ASTM E647. Experimental studies on static crack resistance are carried out for three-point bending using half-size Charpy specimens (55×10×5 mm) for the material - 10GN2MFA steel, which is used as the main metal for the main circulation pipelines of VVER-1000. The reference temperature is determined by processing a set of relevant experimental data.

Improving the shape and dimensional accuracy of hollow semi-finished products during hot reverse extrusion from square workpieces

2024-01-26T13:08:53+02:00

Stamping of round hollow semi-finished products by hot reverse extrusion from round and square workpieces is the first stamping step in the manufacture of hollow products for special purposes. These products require certain mechanical properties along the wall height and in the bottom part, which can be achieved by working out the metal structure by plastic deformation. The bottom part is worked out by reverse extrusion. The wall properties are obtained in the following stages of drawing the semi-finished product with thinning after extrusion. The use of square workpieces results in more intensive working out of the bottom of the semi-finished products during the reverse extrusion. However, as a result of extrusion, four protrusions appear at the end of the semi-finished product wall in places that match the corner areas of the workpiece. The presence of protrusions leads to the need for an additional operation of cutting the end of the semi-finished product before extrusion, as well as to an increase in metal usage. Therefore, an urgent task is to study the method of eliminating protrusions in the semi-finished product and the additional cutting operation.
To improve the accuracy of the shape and size of hollow semi-finished products during hot reverse extrusion from square workpieces.
Elimination of protrusions is achieved by forming chamfers in the corner zones of the square workpiece by preliminary deposition before extrusion.
The finite element method (FEM) was used to model the processes of hot deposition of corner zones on a square workpiece and subsequent reverse extrusion with the dispensing of round hollow semi-finished products. The dimensions of the chamfers on the high-carbon steel workpiece were determined, which ensured the elimination of protrusions at the end of the wall of the round semi-finished product after extrusion. The dependence of the deposition and extrusion forces on the punch movement was determined. The specific forces on the deforming tool were determined. The distributions of stresses, strains, and temperature in the deformed metal at the end of deposition and extrusion are presented. The working out of the metal structure by hot plastic deformation is evaluated. The design of a stamp for deposition and extrusion is developed.
The geometry of a square workpiece with chamfers in the corner zones was determined, which ensures the elimination of protrusions at the wall end during hot reverse extrusion with the dispensing of round hollow semi-finished products

Modeling of the separation process of a two-phase liquid in a high-temperature gas environment

2024-01-25T14:00:34+02:00

Obtaining a high-quality highly dispersed salt solution can be realized from a salt solution by the method of ultrasonic exposure. As you know, concentrated salt solutions can be presented in the form of a gas-liquid medium. The influence of ultrasound, in the case of wetting a surface vibrating with an ultrasonic frequency by a thin layer, leads to the formation of a cavitation layer in the liquid layer and capillary waves on its surface, from the ridges of which, at a certain intensity of oscillations, finely dispersed aerosol droplets are detached.
The detachment of droplets from the vibrating surface leads to the formation of finely dispersed salt aerosol, which saturates the heated air, which is tangentially fed into the cylindrical working chamber with further separation of hydrodynamic processes. Part of the aerosol wets the heated inner surface of the cylindrical chamber with the formation of a thin film, which gravitationally flows down the vertical solid surface and is subjected to active evaporation with the removal of the salt phase, and the second part is subjected to additional grinding and active evaporation in the central turbulent flow and centrifugal turbulent flow of hot air with additional by removing the salt phase. In order to intensify the salt removal process, the surface on which the film is formed can be profiled. Ultrasonic dispersion of the salt solution to a finely dispersed state allows to significantly increase the surface of contact with the heated air, which allows to intensify the diffusion process.

Improving the dynamic positioning accuracy of the electro-hydraulic drive

2024-08-26T13:56:35+03:00

Research is focused on improving the dynamic accuracy of control surface positioning during the switching of hydraulic actuator modes and studying the processes and phenomena that cause control surface overshoot. Existing studies on the dynamic accuracy of hydraulic actuators have been analyzed. Transitional processes occurring in the " electromagnetic recirculation valve – electronic control unit" loop during changes in hydraulic actuator operating modes have been examined. The features of processes and physical phenomena leading to increased activation time of the hydraulic actuator have been identified. Solutions and electrical connection schemes for connecting the hydraulic actuator recirculation valve to the electronic control unit have been proposed to meet the accuracy positioning and activation time requirements.

Experimental studies have been conducted to simulate the operational mode of hydraulic actuators, and failure situations modes under various load forces have been identified. Based on the results, principles for designing connection schemes for the electromagnetic recirculation valve of the hydraulic-mechanical actuator to the electronic control unit, which enhance system positioning accuracy at the structural level, have been formulated. Technical solutions aimed at achieving the specified accuracy and activation time for the hydraulic actuator have been developed and practically tested. The effectiveness and suitability of the proposed solutions for operational use, considering external factors, have been experimentally confirmed.

Alternative technologies of composite highly loaded aircraft structures: a qualitative method of making multi-criteria decisions. Comprehensive presentation: Part IV. Equilibrium and stability of the dynamic model of the ADS

2024-04-29T20:57:08+03:00

The main direction of the fourth part of the work is the study of an autonomous dynamic system in the field of aviation technology, based on the provisions of the qualitative theory of differential equations with the involvement of the phase portrait method. The materials and results of the article are based on the starting points in the decision-making problem (DPR), specified [1], [3] empirically - the formalized direction of research in the comparison of preprego - autoclaved (surfactant) and non-autoclaved VARTM technologies in the manufacture of carbon-plastic aircraft structures according to the prevalence (first of all - quality) (AK) type of highly loaded stringer panels of the wing caisson (VSP) of mainline aircraft. That is, we are talking about a large multi-stage (based on ChTP) technological system. The research as a whole is based on systems analysis (SA) and interpreted structure-functional modeling of ATP. The evaluation toolkit and criterion-evaluation apparatus based on the macro-level ADS and a number of technological structures and other configurations are used [2]. Special points, stability and phase portrait of ADS (quadratic function) were investigated, with the involvement of interpreted elements of the topology of many species, as well as bifurcation points of the system.