Changes In Stress-strain State Research Articles

Determination of Temperature Stresses during the Construction of Massive Monolithic Foundation Slabs, Taking into Account the Subgrade Compliance

Background The problem of early cracking caused by the heat of concrete hardening is relevant for massive reinforced concrete structures, including foundation slabs. The purpose of this work is to develop the methodology for determining temperature stresses during the construction of foundation slabs, taking into account the interaction with the subgrade. Methods The Pasternak elastic foundation model with two-bed coefficients is used for the soil. The temperature of the foundation slab is considered a function of only one coordinate z (temperature changes only along the thickness of the slab). As a result, to determine the stress-strain state of the slab, a fourth-order differential equation for deflection was obtained. A technique for numerically solving the resulting equation using the finite difference method is proposed. The calculation of the stress-strain state is preceded by the calculation of the temperature field, which is performed by the finite element method in a simplified one-dimensional formulation. Results The solution to the test problem is presented for a constant modulus of elasticity of concrete over time. The results were compared with finite element calculations in a three-dimensional formulation in the ASNYS software. The calculation was also performed taking into account the dependence of the mechanical characteristics of concrete on its degree of maturity. In this case, the picture of the stress-strain state changes significantly. The proposed method was also successfully tested on experimental data. Conclusion The proposed approach can significantly save calculation time compared to the finite element analysis in a three-dimensional setting.

Analysis of stress-strain state changes in railway tracks during transition to European gauge

The geographical location of Ukraine facilitates its integration into the transportation network connecting European countries. Various options exist for transitioning from the gauge of 1 520 mm to the European standard gauge of 1 435 mm. This paper aims to analyze the changes in the stress-strain state of railway track elements during the reconstruction of existing sections from the 1 520 mm gauge to the 1 435 mm European gauge or to a dual gauge of 1 435/1 520 mm. To perform these calculations, a spatial model of dynamic deformations in the railway track is employed, based on the principles of elasticity theory. The implementation of a combined railway track complicates the stress state of the ballast layer, leading to asymmetric stresses along the length of the sleepers, which vary depending on the track on which trains operate. There is also a redistribution of stresses acting on the ground structure, which has been in operation for many years. The research results identify changes in the stress-strain state of the railway track and can be used to justify measures for the appropriate reinforcement of the ballast layer and the ground structure.

Cyclic Thermomechanical Loading of Epoxy Polymer: Modeling with Consideration of Stress Accumulation and Experimental Verification.

Developing a viscoelastic model for the cyclic thermomechanical loading of thermosetting polymers is the main goal of this study. The model includes memory for residual thermal stresses and can consider stress accumulation across many loading cycles. By considering stress accumulation, we can improve predictions and understand how thermosetting polymers' stress-strain state changes under cyclic thermomechanical loading. This approach was validated through experimental verification to ensure its applicability in practical engineering scenarios. The experiment showed that the thermosetting polymer can accumulate stress during cycles of heating and mechanical loading during use. The results of the modeling and experiment are compared. The results have led to corrections in the way this model is applied to thermosetting polymers like the epoxy resin in this study. The corrected results matched well with the experimental measurements of stress under cyclic thermomechanical load, with a difference of only 1 to 6%.

MONITORING OF CHANGES IN THE STRESS-STRAIN STATE OF GEOENVIRONMENT AT THE PETROPAVLOVSK GEODYNAMIC TESTING SITE BASED ON THE MULTI-INSTRUMENTAL BOREHOLE AND GPS DATA DURING THE ACTIVE PHASE OF PREPARING THE ZHUPANOVSKY EARTHQUAKE (JANUARY 30, 2016, Mw 7.2)

The paper presents the results of comparative analysis of the data regarding the multi-instrumental borehole monitoring data of changes in the geoenvironment stress-strain state and GPS data obtained in the time vicinity of the close strong Zhupanovsky earthquake. The purpose this study was to assess the feasibility of using GPS measurements on routine basis for effective monitoring of strong Kamchatka earthquakes in the area of Petropavlovsk-Kamchatsky. The Zhupanovsky earthquake active phase was chosen as a "test" time interval for comparing GPS and borehole monitoring data. This earthquake has been the strongest seismic event since 2000 in terms of the ratio of the earthquake focus length to the hypocentral distance. The time series borehole electromagnetic and geoacoustic data were compared with the dilatation series reflecting the relative changes in the area of a triangle composed of Kamchatka GPS observation network located in the Petropavlovsk geodynamic testing site. The analysis indicates a high degree of consistency in these time series. GPS data obtained during the active phase of the earthquake preparation is agree with the results of mathematical modeling expected values of volumetric strain on the daylight surface on the eve of the earthquake. A joint analysis of borehole and GPS data made it possible to specify the time limits for the stages of change in the stress-strain state of geoenvironment and to resolve ambiguity of interpretation of the electromagnetic and geoacoustic borehole measurement results at the final stage of preparing the Zhupanovsky earthquake.

Software for computer simulation of multiphysics processes in electromagnets and actuators of vacuum switching devices taking into account contact interaction of structural elements. Part 2: features of commercial software and open access codes

The first part of the work presented a general overview and classification of software tools for the numerical solution of multiphysics problems of computer modelling of coupled electromagnetic, thermal and mechanical processes in modern complex technical objects, including actuators and electromagnets of vacuum switching devices taking into account contact phenomena when their stress-strain state changes. Criteria for choosing the appropriate software were also proposed and the features of in-house codes for mathematical modelling of technical objects and processes under consideration were analyzed. This paper is the second part of the work and is devoted to a detailed review of commercial codes present on the market and available, as well as open access tools for possible use in performing relevant computational studies, namely, numerical analysis of multiphysics processes in electromagnets and actuators of vacuum switching devices, taking into account contact phenomena by the Finite Element Method. On this basis, taking into account the conclusions regarding in-house codes made in the first part of the work, a selection of specific software for use in the performance of relevant calculation studies is made.

Experimental Studies of Mechanical-Electrical Transformations during the Destructive Processes Developing in Dielectric Materials

A mechanical-electrical method for testing fractures developing within the stress-strain state changes of dielectric rock samples, as an example, is discussed here. The paper discusses the results of numerical and experimental studies of changes in the electromagnetic responses parameters under the pulse deterministic acoustic excitation of rock samples with different composition and texture. The paper presents the results of mathematical calculations of the stress concentration on cracks located along and across the sample axis, perpendicular to which deterministic acoustic pulses were introduced. The cracks presented in the sample volume are stress concentrators. With a different number and sizes of cracks perpendicular to the propagation of an acoustic pulse, the intensity of stresses and their type differ significantly. This circumstance indicates the influence of the structure of the samples and their dielectric properties on the parameters of electromagnetic signals when recording the results of mechanical and electrical transformations. Thus, the use of the method of mechanical-electrical transformations under compression can be used in testing the processes of the onset of crack formation and the development of fracture in solid-state dielectric materials and products.

Experimental Studies of Mechanical-Electrical Transformations during the Destructive Processes Developing in Dielectric Materials

A mechanical-electrical method for testing fractures developing within the stress-strain state changes of dielectric rock samples, as an example, is discussed here. The paper discusses the results of numerical and experimental studies of changes in the electromagnetic responses parameters under the pulse deterministic acoustic excitation of rock samples with different composition and texture. The paper presents the results of mathematical calculations of the stress concentration on cracks located along and across the sample axis, perpendicular to which deterministic acoustic pulses were introduced. The cracks presented in the sample volume are stress concentrators. With a different number and sizes of cracks perpendicular to the propagation of an acoustic pulse, the intensity of stresses and their type differ significantly. This circumstance indicates the influence of the structure of the samples and their dielectric properties on the parameters of electromagnetic signals when recording the results of mechanical and electrical transformations. Thus, the use of the method of mechanical-electrical transformations under compression can be used in testing the processes of the onset of crack formation and the development of fracture in solid-state dielectric materials and products.

Аналіз змін напружено-деформованого стану в суглобовій губі лопатки в умовах різних типів її пошкодження

Актуальність. Пошкодження суглобової губи лопатки є досить поширеною проблемою плечового суглоба. Наявність цієї патології в ділянці задньої порції суглобової губи залежно від типу її пошкодження значно збільшує показники напружень на суглобовий хрящ, що призводить до розвитку та прогресування дегенеративних змін у плечовому суглобі, прискорення артрозу та реалізації задньої нестабільності плеча. Така ситуація націлює хірурга на визначення тактики оперативного втручання, спрямованої на розвантаження пошкодженої ділянки та усунення біомеханічного дисбалансу. Мета дослідження — вивчення клінічно значимих пошкоджень суглобової губи лопатки залежно від типу її пошкодження на основі біомеханічного аналізу змін напружено-деформованого стану (НДС) контактних поверхонь плечового суглоба та обґрунтування тактики лікування цих пошкоджень. Матеріали та методи. Розрахунки НДС елементів плечового суглоба методом скінченних елементів були проведені на основі СКТ-сканів інтактного плечового суглоба за допомогою програмного пакета Mimics в автоматичному та напівавтоматичному режимах, відтворена просторова геометрія плечового суглоба. Засобами SolidWorks створені імітаційні комп’ютерні 3D-моделі інтактного плечового суглоба та з трьома типами пошкоджень суглобової губи. Вивчали НДС на структурах плечового суглоба при різних значеннях кута відведення та ротації плечової кістки (нейтральне, відведення верхньої кінцівки на 0–20–40–60°, внутрішня ротація 0–20–40° та комбінація цих рухів). Критеріями оцінки НДС були напруження за Мізисом, контактні напруження та максимальні деформації. Результати. Усі типи пошкоджень суглобової губи при різних положеннях кінцівки в плечовому суглобі призводять до значного збільшення показників напружень та деформацій у контактній зоні. У нейтральному положенні кінцівки пошкодження суглобової губи І типу викликає збільшення напружень на губі у 8 разів, ІІ типу — у 30 разів, ІІІ типу — у 3 рази порівняно з інтакт-ною моделлю. У положенні відведення кінцівки до кута 60° та внутрішньої ротації 40° пошкодження суглобової губи І типу викликає збільшення напружень на губі в 5 разів, ІІ типу — у 18 разів, ІІІ типу — на 14 % порівняно з інтактною моделлю. Максимальні значення НДС на елементах плечового суглоба (суглобова губа, головка плечової кістки) спостерігаються в положенні відведення кінцівки до 60° та внутрішньої ротації 40°, і вони вищі, ніж у нейтральному положенні кінцівки. В умовах пошкодження суглобової губи ІІ типу спостерігається екстремальне зростання показників напружень в усіх положеннях у плечовому суглобі, як на самій суглобовій губі (у 30 разів), так і на головці плечової кістки (у 2,7 раза). Із збільшенням кута відведення та внутрішньої ротації в суглобі значення НДС на самій суглобовій губі значно збільшуються (у 18 разів), сягаючи значень напружень 101,68 МРа та деформацій 60,77 мм у положенні відведення кінцівки до 60° та при внутрішній ротації 40°. Зростають показники НДС і на головці плечової кістки (в 1,4 раза). Висновки. Виявлено, що найбільший дисбаланс стабілізуючих структур плечового суглоба виникає при відшаруванні суглобової губи та стає критичним при його комбінації з розривом, тоді як сам по собі ізольований розрив не призводить до критичних змін напруження та деформації на структурах плечового суглоба. Доцільно проводити фіксацію відшарованої ділянки суглобової губи при виявленні цієї патології під час артроскопічного втручання, що дозволить збалансувати напруження та деформації на структурах плечового суглоба при здійсненні найбільш типових рухів. Ця процедура дозволить уникнути раннього розвитку артрозу та задньої нестабільності плечового суглоба.

ASSESSMENT OF EXCAVATION INTERSECTIONS’ STABILITY IN JOINTED ROCK MASSES USING THE DISCONTINUUM APPROACH

During ore deposit development, vast networks of excavations are designed, and the volume of their intersections reaches 10%. At excavation intersections, the prediction of stress-strain state changes is complicated due to spatial geometry, the cross-coupling effect, construction sequence, etc. Mechanical properties of rocks, joint set parameters and the initial stress field also have a significant impact on stress redistribution. According to studies, up to 40% of the total number of failures in excavations occur during their intersections’ construction or reinforcing. Loads on the intersection support in accordance with existing methods are determined as for single excavations with an equivalent span and defined as the width of the larger excavation. The trend towards the intensification of mining, an increase in depth and the complexity of mining and geological conditions also complicate stress state assessment. Existing approaches need to be revised and updated for a more accurate prediction of the stress-strain state at intersections, and should consider spatial geometry, joint sets and initial stress field parameters. In this research, discrete element numerical modelling in 3DEC is done and the results are compared with existing empirical methods. Numerical models are created in a spatial setting and contain explicit representations of joints in the rock mass. Models are verified based on in-situ data, and the obtained results show a difference of up to 2 times in comparison with empirical results. This indicates that the reliability of the existing empirical methods is low, which may lead to stability loss on an intersection. Therefore, empirical methods should be updated. This can be done on the basis of numerical modelling, which shows sufficient convergence with in-situ data.

The Effect Of The Actual Stiffness Of Bolted Hinged Joints On The Bearing Capacity Of The Elements

The article investigates the influence of partial stiffness of the hinge joint of single-span and multi-span freely supported beams with lower structures on their stress-strain state under the action of vertical evenly distributed load. Joints of freely supported beams under the action of external load are opened on supports and mounting bolts interfere with their full opening, that is joints work as partially rigid. Knowing some initial parameters of ideally hinged joints, it is possible to establish what influence their change will have both on the calculation scheme of beams, and on calculation schemes of cross frames of frameworks of buildings and constructions, to which they enter, as a whole. The method of initial parameters was used to determine the influence of the resistance of the mounting bolts on the opening of the support joints on the stress state of the elements. The offered technique allows to define real rigidity of any bolted hinge connection taking into account its actual work and to adjust it stiffness by changing the diameter of the bolts, the strength of the material from which they are made, their number, distance between them, as well as use additional material resource by reducing the maximum stresses in the calculated cross sections. This is especially true of elements made of perforated profiles, because the change of stress-strain state in the support zones will cause redistribution of stresses in the calculated points of their cross sections, both on the supports and in the span of the beams. This must be taken into account by including certain coefficients in the calculation formulas, depending on the specific operating conditions.

Electromagnetic Methods for Testing Changes in Stress-Strain State of Dielectric Materials

Electromagnetic Methods for Testing Changes in Stress-Strain State of Dielectric Materials

Study of regularities of changes in stress-strain state of coal–rock mass in fractured zones

The regularities of changes in the stress-strain state of coal in rock mass depending on the main mining geological and engineering factors are identified. Using these factors, it is possible to find the optimal support parameters in specific conditions to increase the stability of preparatory mine workings. The degree of influence of mining and engineering conditions of exploitation on displacements in marginal rocks with various types of support in excavation workings is investigated.

Computer modeling of the process of soil sealing under the pipeline

In the article, using computer simulation in Ansys environment, the working process of replacement equipment of a single-bucket excavator for soil compaction under the pipeline is investigated and the influence of working equipment parameters on the qualitative picture of soil compaction process and change of stress-strain state of main pipeline and soil is evaluated.

Stress-strain state of the building foundations with taking into account the possible water saturation of loess soils

In Ukraine, the problem of construction on loess soils is relevant due to the widespread use of these soils and their negative property - the ability to give additional deformations of subsidence during water saturation. Flooding of territories by groundwater, emergency leaks from aquifers cause significant problems during the exploitation of buildings and engineering structures on such soils.
 Computer simulation of the interaction of the building with the soil base allows to investigate the influence of all negative factors on the change of the stress-strain state of both the soil base and the load-bearing structures of the building.
 The study of the interaction of the building with the foundation was performed using the software package LIRA-CAD. The interaction of the building with the soil base, the soils of which are able to reduce their mechanical properties with increasing humidity and give additional subsidence deformations, was studied. A variant design of the foundations was performed taking into account the occurrence of uneven deformations during subsidence of the loess soil due to its moistening in case of possible emergency losses from aquifers. The change of stress-strain state of the foundations of the building depending on the spatial rigidity of the foundation, the location of the soaking zone within the building spot, the shape and size of the zone of soil moisture is analyzed.
 It is shown that taking into account the possible water saturation of loess soils when calculating the collaborate of the building with the soil base, allows to obtain stress-strain state of foundations and load-bearing structures of the aboveground part of the building for the most unfavorable conditions that may occur. The search for the optimal variant of the foundation structures of the building, which, while remaining cost-effective, provides reliable operation of the building in conditions of possible occurrence of uneven deformations of subsidence of the soil base during water saturation of the layer of loess soils.
 According to the research results, a rational variant of the foundation structures has been designed taking into account the possible occurrence of non-uniform deformations.

IMPROVEMENT OF GEOTECHNICAL MONITORING OF STRENGTHENING OF DEFORMED BUILDINGS ON PILE FOUNDATION

Object. Improve the geotechnical monitoring of the system “deformed building – driven prismatic piles in the composition of the strip grille – soil base with a weak underlying layer” before, during and after the supply of the existing grilles of the monolithic reinforced concrete slab. Method. Standard field and laboratory methods for determining the physical and mechanical properties of soils; normative methods of inspection of a technical condition of bearing building designs, their bases and the bases; methods of mathematical statistics for processing the results of experiments; long-term geodetic observations of deformations of a brick building on a pile foundation before and after its strengthening. Results.A system of geotechnical monitoring and scientific and technical support of the system "deformed building – driven prismatic piles as part of a belt grid – soil base with a weak underlying layer" was developed and tested on a typical natural object before and after supplying monolithic reinforced concrete slabs, in particular: the actual parameters of its foundations and foundations and their changes over time are determined; conducted geodetic observations of the deformations of the object before, during and after its strengthening to establish patterns of development and stabilization of these deformations over time, etc. Scientific novelty. The structural and technological solution of strengthening the foundations of driven prismatic piles in the belt grid by bringing under the existing grilles monolithic reinforced concrete slab and obtained new research data on the change of stress-strain state of the system “deformed building – driving prismatic piles in the belt grid – soil weak underlying layer” due to the supply under the existing grilles of the plate. The practical significance. Developed and implemented in geotechnical practice constructive-technological solution of reinforcement of foundations from driven prismatic piles as a part of a tape grid by bringing under existing grilles of a monolithic reinforced concrete plate and the corresponding technique of geomonitoring.

Modeling of stresses in inorganic composite plates under non uniform high temperature heating

An asymptotic theory of thin composite plates with multi-stage high-temperature phase transformations is proposed. The theory is based on an asymptotic analysis of 3-dimensional equations of the mechanics of composite materials, taking into account phase transformations. Phase transformations are described by a system of kinetic equations, which is solved in conjunction with the equations of internal heat and mass transfer. The so-called local problems for plate theory are obtained and the averaged equations of plate theory with phase transformations are derived. An example of a composite based on an aluminum-chromo-phosphate matrix under uneven heating is considered. A numerical-analytical solution showed that although the heating is uneven due to the peculiarities of phase transformations, the stress-strain state changes significantly in time and is variable across the plate thickness. The developed theory allows us to calculate the stress distribution in the plate with high accuracy.

Investigating the variation of the fields of elastic stresses in the rock mass when developing the Peschanskoye deposit

Research aim is to study parameter variations in the stress state of the rock mass to ensure safe and efficient mining of the Peschanskoye magnetite deposit (Northern Ural) to the full depth, which has been carried out by Severopeschanskaya mine since 1958 in a complex of hard rock at a depth of 200 to 700 m. Blind, thick, and steep ore bodies are developed by a block-caving method with ore breaking to a clamped medium. From a depth of 400 m, the field is classified as rock burst hazardous. The first rock burst was recorded in 1981 at a depth of 450 m. Research methodology includes full-scale experimental measurements of the rock and ore mass stress state at accessible depths and horizons of the deposit, establishing patterns of stress growth with depth, as well as long-term (since 1990) geo-deformational monitoring of an untouched rock mass stress level in time. Research results analysis has allowed to establish the patterns in stress-strain state changes during mining. Gradients of gravitational and tectonic stresses growth with depth are determined. Alternating (astrophysical) stresses are highlighted in a special line, the extreme values of which are linked chronologically with various information factors. Conclusions. The determined values of rock mass natural stress state variation parameters in combination with the established stresses around the workings and goafs (technogenic impact) make it possible to take into account the main tempo-spatial factors of the impact made by the mentioned loads when selecting rockburst-safe and effective mining parameters for underground geotechnology both at the top horizons when applying controlled collapse of overlying blind deposits and in the prevention of rockburst hazard in the lower horizons of the developed field

From surface morphologies to inner structures: insights into hypermobility of the Nixu rock avalanche, southern Tibet, China

Large rock avalanches often result in many deaths and catastrophic damage to infrastructure far from source. No consensus has yet been reached on mechanisms causing their extraordinarily long runout since the first study at the Elm Slide, Switzerland. Much current understanding of rock avalanche kinematics and dynamics has been gained from observations of their surface morphologies and inner structures. Based on field surveys, high-resolution satellite image interpretation, and laboratory sieving, we analyzed the ancient, earthquake-induced Nixu rock avalanche in southern Tibet, China, which has unique exposures of both morphological features and inner structures of the deposits. The study revealed that (1) the Nixu rock avalanche probably could be disintegrated into three emplacement stages, transforming from an initial deep-seated rockslide into a large secondary debris avalanche, plus a relatively small third debris avalanche. The spreading of the secondary debris avalanche contributed to the subsequent long-runout propagation. (2) The morphological features observed in successive proximal to distal exposures (such as scarps, flowbands, transverse ridges, grid grooves, hummocks, and splash zones) reflect the change in stress-strain state of debris in motion from tension, to compression, to shear and tension. (3) The complicated inner structures exposed along river banks (such as jigsaw structures, fragmented clasts, inner shear zones, conjunction faults, convoluted lamination, decollements, sand injections, and intrusions) indicate the existence of a thin basal shear zone and a pressurized entrained substrate between the substrate and rock avalanche debris. (4) This suggests turbulent flow with bulldozing in the front, but a laminar flow under a simple shear model for the main body. (5) The analysis suggests that the rock avalanche’s extraordinary mobility involves a combination of momentum transfer, substrate entrainment, liquefied basal shearing, internal shearing, and rock fragmentation.

Change in stress-strain state of disc brake elements during braking

Change in stress-strain state of disc brake elements during braking

Analysis of models for porosity evolution in reservoir during steam injection

Depletion of traditional hydrocarbon reserves leads to the development of extracting methods for heavy crude oil and bitumen characterized by extremely high viscosity. The most effective technology is the steam-assisted gravity drainage. The aim of this method is to decrease oil viscosity by injection of hot steam into the reservoir. Increase of temperature, pore pressure and change of stress-strain state during this process significantly affect porosity which is the key storage parameter of the reservoir. This work is devoted to the analysis of models for porosity evolution during the steam-assisted gravity drainage process. The authors have developed an original model to describe steam-assisted gravity drainage which includes the mass balance equation for a three-phase flow, the energy balance equation involving latent heat due to vaporization/condensation of water/steam and Darcy’s law for fluid filtration. Numerical implementation of the proposed equations was based on the pressure-saturation algorithm. The results have shown a substantial qualitative and quantitative disagreement between the considered models. Coupling of porosity with volumetric strain leads to the rise of its magnitude. Models relating porosity to pore pressure show simultaneous existence of high-porous (near the injection well) and low-porous (near the production well) areas. In case when porosity is dependent on effective stress a circular area of a compacted soil is formed. Therefore, to obtain a correct estimation of the oil production rate in an arbitrary reservoir it is necessary to define the prevailing mechanism of porosity evolution (volumetric strain, pore pressure or effective stress).