Calculation Of Stress-strain State Research Articles

Modelling of oxide fuel restructuring during first hours after a reactor reaches its power

There is a substantial amount of experimental data that confirm the peculiarity of the oxide fuel behavior during the first hours after a reactor reaches its power. With an increase in temperature during the said period, oxide fuel pellets crack because of a significant temperature gradient. Further developments occur due to the accumulation and redistribution of fission products, and manifest themselves as changes in the fuel matrix porosity and the formation (or diameter increase) of a central hole. The zones that differ in their microstructure, density and thermal conductivity are formed along the fuel pellet radius. As the oxide fuel composition and restructuring result in its thermal conductivity change, it is important to pay attention to the formulas used in the stress-strain state calculations of a fuel element. The methodology for calculating changes in the oxide fuel porosity and the pellet’s internal diameter is proposed and based on the published research papers dedicated to the study of oxide fuel properties and behavior during the first hours after a reactor reaches its power. Тhe methodology was tested using real experimental data on the porosity redistribution along the fuel pellet radius. The presence and the size of the pellet’s inner hole, as well as changes in the fuel matrix porosity, have a noticeable effect on the maximum temperature value. Taking into account the pellet structure evolution while performing computational simulation of the fuel rod operation under irradiation allows assessing the fuel element’s operability more accurately. The proposed methodology can be used in computer codes designed to calculate the stress-strain state of cylindrical fuel elements of fast reactors.

Modeling of ice-matrix composite fracture

This article discusses the results of a study that used the structural approach to conduct multiscale modeling of composite materials. These materials are composed of an ice matrix that has been enhanced with high-strength basalt fibers. The research involved numerical modeling to analyze the fracture process of composite materials made by freezing fresh water with added basalt fibers. The analysis included experimental data from samples of pure ice and composites with different amounts of filler. The effective modulus of elasticity of the composites was determined by considering the quantity of basalt fiber reinforcement. The discrepancy between the strength obtained by finite element complex ANSYS numerical calculation and the experimental data was revealed by a series of macroscopic test calculations of the composite material sample, according to which the effective modulus of elasticity of the composite was recalculated and corrections were introduced into the Voight and Reuss models, taking into account the non-uniform distribution of the fibers and the non-ideal adhesion between the fibers and water ice. A stochastic model of crack growth at the micro level was also used with the data on the diameter and length of basalt fibers and their random distribution in the layers of the composite material. Using the newly acquired effective elastic moduli and the SmartCrackGrowth algorithm, a satisfactory agreement of the crack growth rate with the obtained by stochastic calculation was achieved. The refined method of effective elastic moduli and multilevel model of stress-strain state calculation of composite materials are recommended for assessing the strength of ice cover and designing winter roads with high load-bearing capacity and long operational duration in the Arctic and Subarctic environments.

CALCULATION OF STRESS-STRAIN STATE OF FIBER COMPOSITE ADHESIVE

CALCULATION OF STRESS-STRAIN STATE OF FIBER COMPOSITE ADHESIVE

INVESTIGATION OF THE EFFECT OF TEMPERATURE FIELDS OF DELAYED COKING REACTOR BODIES ON THE STRESS-STRAIN STATE OF THE MATERIAL

The article continues to explore the topic of damage to DCR (delayed coking reactors) or coke drums during operation. Based on the temporary localization of damage formation during the cooling stage, the most critical stage of the technological process during the operation of the DCR is determined and a damage mechanism is proposed in the form of the influence of an uneven temperature distribution over the DCR body. The description of method for studying the temperature field on the outer surface of the body of the DCR using original mobile temperature measuring devices is given. The results of research with data on the distributions and actual values of temperature differences along the outer surface of the body of the DCR during operation are presented. The DCR with a material design made of stainless steel was selected as the object of research. The case of damage in the form of cracking of the welded joint of the body during the operation of the DCR with the occurrence of a leak is considered. To justify the occurrence of damage in the form of corrugations, calculations of the stress-strain state (SSS) of the material of the body elements are carried out. The applied finite element complex «ANSYS» is used for calculations. As the initial data for SSS calculations, the results of studies of the temperature distribution over the outer surface of the DCR are used. During the calculations, it was found that at the cooling stage, the greatest stresses in the body material correspond to the level of the yield strength of the material and lead to irreversible plastic deformation with the occurrence of the process of accumulation of deformations (ratcheting process). A comparison is being made with data from foreign studies of the operating conditions of the DCR. As measures to prevent operational damage to the DCR, it is proposed to change the technical requirements for steels for the manufacture of main parts in terms of increasing the level of mechanical properties (tensile strength and yield strength). Recommendations are formulated on the material execution of the DCR, the design and manufacture of the DCR.

Computer simulation of stress-strain states in zygomatic bones after complex installation of implants

The research addresses evaluation of stress-strain state (SSS) in the “zygomatic bones–implants–denture base” system by varying the type and number of the zygomatic implants, as well as applying loads. The load magnitude was varied over a wide range, characteristic of the mastication process. Changing the adhesion conditions at the “zygomatic implant–bone tissue” interface varied both the level of maximum stress and the location of the critical stress concentrator. The local violation of the integrity of bone tissue in the skull was one of the key reasons for the redistribution of stresses in the “zigomatic implant­denture base” system. Such a phenomenon should be primarily taken into account when choosing the standard sizes of installed zygomatic implants in order to reduce the compliance of weakened areas of the skull (as the basis of the load-bearing structure). Based on the results of the FEM-based computer simulation, the algorithm was proposed for planning prosthetic treatment, which involves the iterative method for selecting both size and location of installing zygomatic implants depending on the results of the SSS calculation and the onset of a critical condition (primarily in bone tissue at the contact area with zygomatic implants).

ПРОГНОЗУВАННЯ НЕСУЧОЇ СПРОМОЖНОСТІ ПЛИТНОГО ФУНДАМЕНТА ЗА ЧИСЛОВИМ МЕТОДОМ ГРАНИЧНИХ ЕЛЕМЕНТІВ

Construction is one of the leading branches of the national economy in the historical aspect of its development. The first design task is to determine the strength of building structures. Therefore, the study of the stress-strain state and related calculations are the most important in construction. The purpose of studying soil mechanics and foundation construction techniques is the calculation and construction of structures on or in soil. The main task is the construction of structures with a sufficient degree of reliability.The selection of an adequate theoretical model remains the main problem of soil mechanics. Indeed, the deformation of the dispersed granular material of the soil takes place during the mutual sliding of the grains, the rheology of the soil is complex, as evidenced by a large amount of experimental material. Today, the path of development of soil mechanics is related to the study of problems within the framework of the elastic-plastic dilatation model and the improvement of this model based on experiments. A mathematical model of a technical object at the micro level is a system of differential equations in partial derivatives, the exact solution of which can be obtained only in a few partial cases, therefore a discrete model is built using numerical methods that use the Poisson idea that the behavior of a complex model can be represented by the behavior of its individual component elements. The intensive development and widespread use of computers significantly brought fundamental mathematical problems closer to applied ones, and strengthened their mutual influence.The emergence of a new, powerful and general method of research - a numerical experiment, more than ever before closely connected the physical content of the problem, its mathematical formulation, numerical methods of calculation and modern computers. The work uses the numerical method of boundary elements. A promising way to develop foundations and foundation structures is to use the ratios of the theory of plastic flow, and the level of development of soil mechanics significantly affects the economy and reliability of the decisions made.

METHOD OF ANALYSIS OF THE STRESS-STRAIN STATE OF A BASE-CENTERING DEVICE AND A PIPELINE WHEN CARRYING OUT THE COMPLEX OF EMERGENCY AND RECOVERY REPAIRS

Link for citation: Rakhmatullina Yu.A., Alekseev V.A., Sultanmagomedov T.S., Khasanov R.R. Method of analysis of the stress-strain state of a base-centering device and a pipeline when carrying out the complex of emergency and recovery repairs. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 7, рр.7-16. In Rus. The relevance of the research is caused by the need to carry out calculations of the stress-strain state of the support-centering device and the pipeline, when the device under consideration is exposed to it, when the axes are displaced due to the presence of residual stresses when carrying out a complex of emergency repair by cutting out a defective section of the pipeline. The purpose of the study is to assess the possibility of using the design of the device and to calculate the stress-strain state of the device when the axes of the boundary sections of the pipeline are displaced due to the release of prestresses during the emergency repair complex for cutting out the defective section of the pipeline. Methods: methods of classical theoretical mechanics, soil mechanics, finite element method. Results. Based on the patent, a preliminary 3D model of the support-centering device and a method for analyzing the boundary conditions and loads affecting the device and the pipeline during the emergency repair complex were developed. The calculation of SSS (stress-strain state) was carried out, where the following results were obtained: when the frame is displaced down/up by 100 mm in the device, respectively, along the length and displacement, stresses arise at the junctions of the enclosing ring and the frame, as well as on the «lugs», exceeding the yield strength of steel; the coefficient of friction μ for the considered diameter of 1020 mm should not exceed 0,15 to prevent the occurrence of areas of plastic deformation of the pipeline during the emergency repair complex for cutting out a defective area in swamp conditions.

Research of the stress-strain state of the loaded assembly for friction welded device

This article presents the results of the study of methods for friction welding of dissimilar materials and the calculations to determine the structural strength of the most loaded part of a special friction welding device were made. The analysis showed that the friction welding method has wide technological capabilities and it is used in various industries. The designs of existing devices and machines for friction welding were also investigated. It was revealed that the method of friction welding in the conditions of machine-building plants of the Republic of Kazakhstan (RK) has not found application due to the little knowledge and high cost of technological equipment. The authors have developed a special device for friction welding of dissimilar materials. To optimize the parameters of the parts, in particular the bracket part, the stress-strain state calculations were performed using the ANSYS software package and the strength calculation by determining the acting external critical loads. The results of the calculation showed the applicability of the developed design of the bracket part.

ЗАСТОСУВАННЯ МЕТОДУ ГРАНИЧНИХ ЕЛЕМЕНТІВ ДЛЯ РОЗРАХУНКУ НАПРУЖЕНО-ДЕФОРМОВАНОГО СТАНУ ПРИ КРУЧЕННІ ТОНКОСТІННИХ РАМ АВТОМОБІЛІВ

Currently, the main method of calculating the stress-strain state (SSS) is the finite element method (FEM), implemented in software packages such as ANSYS, Solid Works, MATLAB, and others. It is established that if the SSS structure is described by rod functions, then the finite element method gives accurate results. If the state of the object is described by other functions, then MSE can give only approximate results of SSS calculation. Therefore, in this work, the authors applied a more accurate method of calculating the SSS of thin-walled car frames – the numerical analytical method of boundary elements (NA BEM). The purpose of the study is to apply a more accurate method of calculating the SSS of thin-walled car frames with the help of BEM. The scientific and practical direction of the work is that the technology of a more accurate method of calculating the SSS of thin-walled car frames - NA BEM is applied. The research methodology is the construction of mathematical models for the calculation of thin-walled car frames – NA BEM. When designing thin-walled metal structures, SSS is described by hyperbolic functions, and FEM, in principle, cannot provide accurate results for calculating SSS of thin-walled structures. Therefore, in the work, it is proposed to apply the technology of the boundary element method, which is free from the shortcomings of FEM technologies, to calculate SSS torsion of thin-walled car frames. The paper presents the matrix functions of the solution of the differential equations of the finite torsion of thin-walled frames, which were used to calculate the SSS of the rod torsion of thin-walled car frames. A more accurate SSS calculation of thin-walled car frames has been performed. This, in turn, will make it possible to determine the exact dimensions of the cross-section of thin-walled car frames. The result of the conducted research is the construction of accurate models of the stress-strain state during torsion of thin-walled car frames. Systems of linear equations of the SSS calculation algebra of limited torsion of two inseparable beams, which are models of car frames, are given. The calculation of frames for compressed torsion is presented. Отримані точні результати розрахунку SSS обмеженого кручення рам автомобілів, що представлені у вигляді таблиць і епюр. Keywords: FEM, BEM, thin-walled car frames.

Evaluation possibility of the turbine disks using of converted aircraft engines of the NK family

The article examines the possibility of using converted aircraft engines for gas pumping units using the example of the main parts of the GTE - the disks of the NK-8-2U aircraft engine and the NK-16ST and NK-16-18ST ground engines. For all disks of the second stage of low-pressure turbines of three engines, the stress-strain state calculation was performed using the boundary integral equations method (BEM) and using the FEM in the Ansys program. For three disk stress concentrators, the theoretical stress concentration coefficient was determined and the maximum equivalent stresses were calculated. During long-term operation, the main parameters of engine operation change due to degradation changes (wear, erosion and corrosion, development of seals, contamination and resizing of flow parts). As a result, the main parameters of engine operation change, in particular, the rotation speed of the rotors and the gas temperature in the turbine, which determine the stress-strain state, which must be taken into account when predicting durability. The compliance of the results of the calculated study of the stress-strain state of turbine disks with their real load was confirmed by the data of their metallurgical study after prolonged operation. Using the Manson formula for the disks of three engines, their cyclic durability was determined before the formation of a crack of low-cycle fatigue. Using the linear damage summation hypothesis, the total damage rates (under static loading and under fatigue loading) for the disks of three engines were calculated. It is established that after the conversion of aircraft engines that have spent their life in flight operation, it is advisable to continue the use of turbine disks on ground-based GTU.

CALCULATION AND EXPERIMENTAL RESEARCH OF TANK HYDRAULIC TRANSMISSION LAYOUT

In order to substantiate the advanced technical solutions of radial hydrovolume transmissions, it is necessary to study the stress-strain state of their most responsible and loaded elements. In particular, it is of interest to determine the rational parameters of cylinder block, which is subject to significant pressure of working fluid. This leads to the formation of a stress-strain state with a high level of stresses and elastic displacements. They can be dangerous in terms of strength, rigidity and performance of the hydraulic transmission in general. To carry out numerical studies of the stress-strain state of cylinder block of hydrovolume transmission at the design stage, finite element models with varied parameters are developed. However, at this stage of research, it is desirable to have a verified numerical model. For this purpose, the paper describes the computational and experimental studies of the layout of the cyclic part of the hydrovolume transmission cylinder block. On the one hand, these studies were performed using the experimental method of holographic interferometry. On the other hand, calculations were performed using the finite element method. In the course of comparison of the received results, the finite element model parameters are determined which provide high accuracy of the stress-strain state calculation of hydrovolume transmissions cylinder block. Keywords: stress-strain state; hydrovolume transmission; finite element method; cylinder block

On calculation of stress-strain state of steel closed ropes in extension and twisting. Part 2. Influence of torsion on the stress-strain state of closed rope

Comparative analysis of the results of determination of stress-strain state in a closed lifting rope during extension and twisting was conducted via analytical calculation according to the linear static equations and computer-aided finite element modeling. Computer modeling allows to establish the features of variation of internal axial forces and torques in the layers that are laid with different directions. It makes possible to predict workability of a closed lifting rope during operation. The most intensive redistribution of internal forces and torques in the internal and subsurface layers during rope turns under the effect of external torque was found out in comparison with extension. Decrease of the torque and axial force values to zero in the deposited external layer during its untwisting testifies about switching this layer off the operation and possibility of rope lamination in the case of external pressure absence. Internal compression of subsurface layer from the side of external rope layer, in its turn, decreases possibility of stability loss (opening) of this layer during its twisting. Deviation from the common rule for variation features of relative elongation ε during joint extension and twisting was shown during modeling. So, external untwisting torque tries to extend the rope (increase of ε), while twisting torque tries to compress it (decrease of ε), what is connected with influence of gap values between the rope elements (wires and layers) on distribution of the contact stresses between them during twisting.

Расчетное обоснование сооружений примыкания батопорта сухого дока с учетом поэтапности возведения и комплексных нагрузок

The article presents the results of calculated studies of the strength of the abutment structures of the floating dam of the dry dock. The calculated studies were carried out on the basis of the spatial finite-element model of abutment, in which there were simulated the enclosing walls of the pipe sheet pile, reinforced concrete abutment, soil of the base and filling. The results of stress-strain state and strength calculations have shown that the maximum displacements of the structures, stresses in the pipe sheet pile, ground anchors and reinforcement do not exceed the maximum permissible values. On the basis of the computational studies performed, the abutment structures of the floating bulkhead were substantiated. The abutment of the floating bulkhead to the dry dock structures serves to support it and transfer the pressing forces of the floating bulkhead to the ground. The enclosing abutment structures of the floating bulkhead are designed as vertical walls made of pipe sheet pile with a reinforced concrete abutment structure in the upper part. To ensure strength, a traditional solution was adopted with the anchoring of the pipe sheet pile with steel rods and ground anchors. To create a waterproof circuit, the project provides for the deepening of the pipe sheet pile into the rock base, the filling of the pipe cavity with concrete, welding of the locks with a metal plate with the filling of the cavity with polymer resin.

On calculation of stress-strain state of steel closed ropes in extension and twisting. Part 1. Determination of generalized stiffness and deformation coefficients

Comparative analysis of the results of determination of generalized coefficients of stiffness and deformation for closed hoisting rope in extension and twisting was conducted via analytical calculation, using generalized static equations and computer finite element modeling. Computer modeling allows to determine the resulting values of axial force P and torque M in closed rope via summarizing of the values of internal forces and torques in the layers that are laid with different directions. It decreases calculation w orkability for the rope stress-strain state. It is shown that the results of analytical calculation of generalized stiffness and deformation coefficients in rope twisting differ by 24 % in average with the results of finite element calculation, based on the static equations. The value of rope elasticity module Ек corresponds to the values of elasticity module for closed ropes during the first loading. Analytical calculation provides the values of Ек module exceeding by 6–7 % the average value of elasticity module of closed ropes (Ек = 160 GPа), that is achieved by preliminary elongation (elastic-plastic extension). It was established that analytical calculation of the stiffness coefficient in twisting does not provide the reliable results owing to absence of accounting the difference in directions of laying of rope layers. Coincidence or opposition in directions of laying of rope layers and torque determines respectively extension or compression of rope layer wires in twisting. Untwisting of the external layer, consisting of Z-shape wires, leads to unloading of the layer and gap forming between wires, while this gap exceeds the allowance on wire dimension and promotes violation of rope structural integrity.

Trial design of umbrella type shell structures

To create aesthetically expressive and functional small architectural forms, it is advisable to use reinforced concrete umbrella type shells in the shape of surfaces that can be specified in an analytical form. Hard landscaping is a suitable field of application for insufficiently studied and tested structures, in contrast to large structures of high importance class. The paper gives an example of a trial variant design of a small garden and park structure in the form of an umbrella type shell, during which different types of umbrella surfaces were analyzed and three variants were selected. Among the studied forms are the following surfaces: a paraboloid of rotation, an umbrella-type surface with a sinusoidal generator, an umbrella-type surface with radial waves based on cubic parabolas (with central flat point). The calculation of stress-strain state of three shells under their own weight was carried out using the finite element method and the peculiarities of working under load of each type of structures were revealed, recommendations are given when designing similar structures.

Accounting method for residual technological stresses in modeling the stress-deformed state of a railway wheel disk. Report 2

The actual problem of increasing the service life of stamped-rolled railway wheels is a complex problem. Residual technological stresses, which cannot be completely eliminated, have a significant effect on the stress-strain state of the wheel as a whole and its disk in particular. At different stages of roughing wheels machining, the residual stress field is continuously changing. This makes it difficult to take into account the residual stresses in the wheels strength calculations. In Report 1 of this work, an accounting method for residual technological stresses was proposed, the essence of which is to set the value of interference between hub and axle when modeling is greater than the actual one. This approach made it possible to obtain additional stresses in the wheel, which adequately reflect the effect of residual technological stresses. In this part of the work, the authors have carried out practical implementation of the developed method and assessment of the degree of residual technological stresses influence on stress-strain state of the wheel disk under the action of operational loads. With regard to the design of a 957 mm diameter wheel with a flat-conical disk (GOST 10791 – 2011), calculations of stress-strain state of the disk under the action of mechanical types of load have been performed. The 60 % increase in the interference between hub and axle realized in the calculations made it possible to establish that the presence of residual technological stresses in the wheel causes an increase of 5 – 38 % in maximum equivalent stresses in the disk zones most loaded during operation. Thus, the proposed method for residual technological stresses accounting allows obtaining an upper estimate of the wheels strength characteristics, and, therefore, more adequately predicting their service life.

Advancing of the geomechanical forecasting system and substantiation of mining at rockburst hazardous deposits

The paper presents the main approaches and their advancing for the systems of rock mass stress-strain state forecasting during mining of adjacent rockburst hazardous deposits. Such systems based on the original Sigma GT software are used at several Russian mining companies which develop solid rock deposits, prone to brittle fracturing and undergoing the gravitational-tectonic stress-strain state. At that, the mining-induced impact on the rock mass is accompanied by occurrence of dynamic rock pressure. The geomechanical situation forecast systems have been applied directly at mining companies for more than 10 years and have shown their high efficiency. The efficiency is associated primarily with the operative calculation of stress-strain state in case of exacerbations of the geodynamic situation and the potential consideration of various mining options in order to reduce stress concentration and give recommendations for supporting and unloading measures in mine workings. In addition, the Sigma GT software is used in annual and long-term mining planning. Initially, such systems were developed for individual rockburst hazardous mining blocks, and their efficient operation time was limited to a 3-5 year period, that is, the block mining time. Further on, taking into account the needs of companies, the systems began to include a whole deposit or even several deposits. Being applied, the system is constantly developed and advanced and adapted to specific conditions and tasks. The most actual tasks are combination of the results of stress-strain state modeling with seismic monitoring data; creation of a hierarchical system of interconnected multiscale volume models; more complete consideration of structural heterogeneities of the rock mass and development of a recommendation block for safe mining operations, taking into account the geomechanical situation forecast data. The solution of these problems is considered on the example of a section of the Khibiny apatite arc, within which underground and open mining is carried out in the zone of mutual influence.

Analytical and Numerical Study of Biaxial Bending on VHCF Testing Machine

Modern VHCF testing regimes are studied. A new loading scheme applicable to a piezoelectric fatigue testing machine is proposed. The scheme is studied analytically and numerically. The analytical part comprises the calculation of the specimen’s geometry to operate correctly on the VHCF testing machine, as well as the specimen’s stress-strain state calculation during an experiment in order to determine the one’s durability. A model based on a kinetic damage equation is introduced. This model is used in the numerical experiment. The behavior of a finite-element specimen in a fatigue experiment is calculated from the beginning up to the stage of active crack growth.

Calculation of residual stress-strain state of deposited steel sheet plates

The Paton Welding Journal, 2021, №05. International Scientific-Technical and Production Journal «The Paton Welding Journal» «The Paton Welding Journal» has been published monthly since 2000 in English, ISSN 0957-798X. «The Paton Welding Journal» is a cover-to-cover English translation of the «Avtomaticheskaya Svarka» (Automatic Welding) journal. The «Avtomaticheskaya Svarka» journal has been published monthly since 1948 in Russian, ISSN 005-111X.

MATHEMATICAL MODELING OF THE PROCESS OF POSSIBLE DAMAGE TO NPP PIPELINES DUE TO THEIER LOCAL EROSION AND CORROSION SINKING

The article is devoted to computer modeling of the process of possible damage to the pipelines of nuclear power plants that received local thinning of the walls.The geometric features of pipelines are essential not only for assessing the intensity of erosion and corrosion of a metal, but also for the final strength assessment, in particular, when calculating local thinning of the walls of pipelines. The accuracy of forecasts of the life of pipeline structures directly depends on the ability to evaluate the strength of pipeline elements that have received local thinning, especially if these elements themselves have a complex shape. Such elements include elbows, nozzles, adapters (transitions), shells. All of these elements are thin-walled structures of complex shape. Computer modeling of the process of crack formation and growth requires solving several problems. A review and critical analysis of the available experimental information on the growth rates of cracks in specific structural materials and in the environment that is characteristic of given operating conditions is required. An assessment of the crack growth rate is impossible without determining the stresses and strains in the shell structure of complex spatial geometry. The development of routine criteria for crack growth and their attachment to a stress-strain state calculation program is the next task. To solve these problems, a complex of three-dimensional finite element methodologies and programs based on the theory of thick shells has been created. The article presents some results of calculating the stress-strain state of adapters and the growth of cracks in them.