Stress-strain State Research Articles

Research of Asymmetric and Symmetric Cold Rolling Influence on Microstructure, Mechanical Properties and Stress–Strain State of Steel Strips

Research of Asymmetric and Symmetric Cold Rolling Influence on Microstructure, Mechanical Properties and Stress–Strain State of Steel Strips

The Effects of Loading Angles on the Failure of Cross-Ply Notched Bio-Basalt Composites

A cross-ply basalt V-notched butterfly specimens were subjected to pure tension, combined tension-shear, and shear stress-strain state using a modified Arcan test fixture with loading angles from 0° to 90° with 15° increment. Multiaxial stress and strain states were studied using the principal stress and strain ratio, from which the principal angle was determined and used to represent principal states in the gauge section. The quasi-elastic to non-linear transition stresses were determined for each loading angle. In biaxial stress-strain states and pure shear, the deformation and consequently the shear-induced damage start to accumulate significantly. Also, in biaxial stress-strain states between 15°-75°, the shift from tension-shear to pure shear was observed after the transition to the non-linear part of the stress-strain curve. The digital image correlation (DIC) images and microscopic evaluation show that a large extent of damage is the consequence of the shear deformation after the rotation of 0° clamped fibres, while the 90° fibres maintained their original straight form. In off-axis tests, the principal strain axis rotates towards the weakest material axis even at small off-axis angles. This causes a transition from a tension-shear biaxial state in the linear loading part to shear in the non-linear part, leading to irreversible damage beyond the transition point.

TESTING OF ROCK SAMPLES FROM OIL AND GAS FIELDS TO DETERMINE THEIR PHYSICAL AND MECHANICAL CHARACTERISTICS

Determination of the physical and mechanical properties of anisotropic limestone rocks is an important and urgent task, since carbonate deposits are very often found in oil and gas fields of the Mangistau region. The data show that limestone creates from 70% to 90% of all problems related to the stability of wells, which is due to the peculiarities of their physical and mechanical properties. Experimental studies of the physical and mechanical properties of limestone have features both in terms of monolith selection and in terms of preparation of samples for research, and in the methods of conducting and processing experiments. These features are due to extremely low permeability, anisotropy of elastic and strength properties due to their layered structure. The experience of testing core samples of layered limestone is considered, tests are carried out on equipment under the program of consolidated-undrained loading in accordance with the standards. As a result of experiments on core samples cut at an angle, along and across the layering, the anisotropic elastic properties of rocks, as well as their dependencies on geophysical parameters, were studied. The anisotropy of elastic properties has a significant effect both on the stress-strain state when solving specific problems of continuum mechanics and on the design values of the initial stress field as a whole. Taking into account the anisotropy parameters obtained in this paper will make it possible to solve Geomechanics problems in relation to layered limestones of the Sarmatian stage.

Experimental Study on Damage Constitutive Model of Rock under Thermo-Confining Pressure Coupling

Underground engineering frequently encounters the challenges of high temperatures and high confining pressures. The combined effects of temperature and confining pressure can significantly alter the mechanical properties of rock. Evaluating the impact of these factors on rock is a crucial aspect of engineering. This study investigates the mechanical properties of rocks under various temperature and stress conditions, focusing on the deformation and failure characteristics of four typical rock types: granite, red sandstone, gray sandstone, and shale under temperature-confining pressure coupling. The results indicate that high temperatures cause internal structural damage and crack propagation in rocks, leading to a reduction in compressive strength and elastic modulus. Conversely, high confining pressures can inhibit crack propagation and enhance rock deformation capacity. Additionally, significant differences were observed in the mechanical responses of different rocks; red sandstone and shale predominantly exhibited shear failure under the coupled effects of temperature and confining pressure, whereas granite and gray sandstone exhibited bulging failure. Based on the experimental results, an elastic modulus fitting model considering the temperature-confining pressure coupling effect was proposed, and the parameters of the Drucker–Prager criterion were modified. A constitutive model was constructed to accurately reflect the stress–strain state of rocks under the coupled effects of temperature and confining pressure. The constitutive model results show good agreement with the experimental findings.

АНАЛІЗ ХАРАКТЕРИСТИК ЛОКАЛЬНОГО НАПРУЖЕНО-ДЕФОРМОВАНОГО СТАНУ З'ЄДНАННЯ МЕТАЛЕВОГО КОМЛЯ З КОМПОЗИТНОЮ ЛОПАТТЮ ПОВІТРЯНОГО ГВИНТА

The article discusses the possibility of modeling the stress-strain state (SSS) of the connection of the metal butt with the composite cylindrical part of the blade using the specialized ANSYS software application and its Composite PrepPost module. Created connection models in ANSYS environment. The optimal designs for connecting the metal butt and composite material have been determined. For a simplified calculation of the connection strength, only the influence of the centrifugal force arising during operation of the screw is taken into account. In the ANSYS software package, a static load of the connection was carried out, which makes it possible to evaluate the nature of the stress distribution in the connection. A butt model and a finite element connection mesh were created. For the calculation, the characteristics of the materials of the blade elements are given. To determine a rational structural-power connection scheme, varying parameters were selected: the number of rows of spikes along the radius, the number of spike belts and the arrangement of the butt spikes. The dependence of the voltage in the composite part of the connection on the arrangement of the butt spikes was obtained. The shape and length of the spike were analyzed. The dependence of voltage on the radius of curvature of the tenon was obtained. The stress-strain state of a tenon-rounded flange is shown in ANSYS. The dependences of voltage on the length of the spike were obtained. The calculation showed that the length of the tenon L has a significant effect on the strength characteristics of the connection between the flange and the composite layer. To determine the rational position of the stud, a calculation was carried out in the ANSYS environment with a shift of all rows of studs by the amount K from the extreme position in engagement with the composite layer and a change in the linear order of the studs to a staggered one. The results of the calculation in the ANSYS environment are presented as a dependence of stress on the displacement K. A flange model is presented, where the stud arrangement is staggered, and the result of the stress calculation in the ANSYS environment. The calculation showed that changing the order of the studs from linear to staggered reduces the maximum stress to 385 MPa. The hydraulic pressure tests confirmed the calculation results. The simulation results showed a significant improvement in the mechanical performance of the joints with minimal design costs.

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.

КРАЙОВІ ЕФЕКТИ В БАЛКАХ ІЗ КОМПОЗИТІВ

Beams made of composites are widely used in aircraft structures, various machines and mechanisms. The experience of operation and repair of such objects shows that when designing beams and spars, one must take into account such effects as the influence of thermal stresses and the additional contribution of Poisson's coefficients to the stressed state of beam elements both in the length direction and along the width beam elements. Scientific studies devoted to the assessment of the stress-strain state of load-bearing structures made of composites demonstrate the conclusions that the effects of thermal expansion (contraction) of heterogeneous connected elements and the influence of Poisson's ratios give significant increases in stress. The value of these increases can be up to dozens of percents of the base load (that is, without taking these effects into account).The paper proposes an engineering mathematical model that allows estimating the value of normal and shear stresses from thermal loading and Poisson stresses. An analysis of the distribution of these stresses along the length and width of the beam elements was carried out.When using the structural-technological solution of beams with sub-shoulders, the proposed method allows you to reasonably choose adhesive or binder for reliable connection of the cap with sub-shoulder, as well as more correctly justify the geometric dimensions of the beam elements. Also, this technique can be used to develop new structural and technological solutions for beams and other load-bearing elements (ribs, walls, webs, doublers, overlapping joints of composite parts).Another applied direction of using the developed methodology can be considered the development and optimization of existing technological processes for the production of parts and units of composites, in which the so-called hot polymerization of the binder (at elevated temperatures) is used. The method makes it possible to estimate the level of thermal stresses that occur during the manufacture of the unit.In general, the proposed technique makes it possible to understand the principles of additional stresses occurrence, to estimate their absolute values, and to increase the accuracy of estimating the stress-strain state of beam elements.

Developing the use of domestic photoelastic coating materials to determine the deformation of parts of complex geometric shapes

The paper presents the results of using some domestic materials in the manufacture of photoelastic coatings to study the stress-strain state in the process of strength testing of parts and assemblies of complex geometric shapes. Based on the analysis of the market for domestic materials for the production of photoelastic coatings, several materials were tested, their mechanical and optical characteristics were determined, and the technology for the production of photoelastic coatings was developed. This paper presents comparative results of a study of the stress-strain state (SSS) of a number of samples and products of aviation and space technology of different levels of complexity, prepared with domestic and foreign photoelastic coatings.

Assessment of the Influence of Features of Crack Formation in Reinforced Concrete Products on their Fire Resistance

The paper considers possible scenarios of cracking during heating and their impact on fire resistance using the example of a bending reinforced concrete structure (beam). It is shown that if the calculated critical temperature of reinforcement is less than the critical temperature of concrete (this indicates a significant load on the structure), then cracks in the tensile zone of concrete are formed after reaching the second stage of the stress-strain state. The concrete of the protective layer does not have time to degrade, the depth of the crack remains constant, and the fire resistance limit is calculated taking into account that the thickness of the protective layer of concrete is reduced by the depth of the crack opening. If the calculated critical temperature of the reinforcement is greater than the critical temperature of the concrete (this indicates a slight load on the structure), then cracks are formed as a result of the degradation of the surface layer of concrete. Their depth should constantly increase with the progression of the concrete layer heating to the critical temperature. In this case, the calculation of the fire resistance limit can be performed without taking into account the formation of cracks. Based on the considered assumptions, a methodology for assessing the impact of cracks on the fire resistance limit of bending reinforced concrete structures is proposed, which consists in analyzing the possibility of open cracks (which is facilitated by heating) and estimating their depth. At the next stage, the heating time of the concrete layer to the crack opening depth τΔ1 and the temperature in the crack after this time are estimated. Next, the time until the critical temperature of the reinforcement τΔ2 is estimated when the concrete layer is heated from the bottom of the crack to the reinforcement. The fire resistance limit is defined as the sum of τΔ1 and τΔ2. The results of the calculations according to the proposed methodology showed that the presence of open cracks in bending reinforced concrete structures can almost halve the fire resistance limit.

Влияние демпфирования по Рэлею на устойчивость земляного полотна железной дороги в условиях сейсмического воздействия

Purpose: to consider the problem of railway subgrade stability under seismic conditions. Show the need to increase stability during an earthquake. Determine the possibility of increasing seismic resistance by introducing a damping layer into the structure. Determine the optimal damping parameters, taking into account the rational use of subgrade materials. Methods: calculations of embankment stability are carried out using the method of G. M. Shakhunyants. An earthquake is taken into account through an increase in shear forces acting on the cells of the sliding massif. The maximum accelerations of the compartments are determined based on the results of finite element method dynamic calculation of a stress-strain state of the embankment during an earthquake, which is specified through an accelerogram. Results: the effectiveness of using a damping layer in the embankment structure, introduced to increase seismic resistance, has been shown. The dependence of the stability coefficient of the embankment on the Rayleigh parameters of the material composing the body of the entire embankment has been determined. For the best material parameters, the optimal thickness and position of the damping layer in the structure are determined, at which the stability coefficient takes on a standard value and the volume of the damping layer is minimal. Practical importance: as an alternative to the normative approach, the possibility of increasing the stability of a railway embankment under earthquake conditions by introducing a damping layer into the structure is presented. An algorithm for selecting optimal damping parameters has been determined in order to increase seismic resistance.

Simulation of creep of a rectangular wooden beam under prolonged static load

Objective. Depending on the stress level, the operation of wooden beams under prolonged load is characterized by both linear and nonlinear creep. This has been shown by numerous experimental studies of wood. The theoretical description of these processes is poorly studied or presented extremely rarely. One of the priority areas in the calculations of wooden structure elements is the derivation of resolving equations of linear or nonlinear creep for various types of stress-strain state. Method. The Maxwell-Thomson equations are used as relations establishing the relationship between stresses and deformations. The technique was tested by comparing the solution with the calculation of well-known researchers. An example of calculation is given for various boundary conditions for fixing a beam of rectangular crosssection loaded with a uniformly distributed load. The deflection value is determined by the grid method. Result. A program has been developed for calculating in the MATLAB package with the possibility of varying the initial data and displaying a graph of the dependence of displacement, bending moment on time. The comparison of the maximum deflection value with the analytical solution is given. It is noted that the stresses practically do not change during creep. Conclusion. The proposed approach can be applied to the analysis of the stress-strain state and bearing capacity of wooden beams of arbitrary cross-section. There are no restrictions on boundary conditions and loading type, and the beam material can be not only wood, but also fiberglass.

Establishment of ductile fracture locus of 2219 aluminum alloy at cryogenic temperature

Abstract Cryogenic forming has been used to manufacture intricate curved surface aluminum components. The special geometry and mold constraints cause the stress state to continuously evolve. Coupling with the cryogenic temperature makes the deformation process more complicated. Especially for the final fracture, which greatly determines the forming quality of the components. Thus, the cryogenic fracture behavior of three typical stress states was obtained by conducting tensile experiments. Fracture strains and stress paths were obtained using a hybrid numerical-experimental method. Finally, the cryogenic fracture locus was obtained based on the MMC ductile fracture criterion. The results indicate that the AA2219-O exhibits superior ductile fracture properties at cryogenic temperature. The fracture strain of AA2219-O was increased by 52.6% at the uniaxial tensile stress state, and by up to 80.0% at under plane strain stress state. This research has a guiding significance for cryogenic forming.

LONGITUDINAL-RADIAL VIBRATIONS OF A VISCOELASTIC CYLINDRICAL THREE-LAYER STRUCTURE

The paper considers a cylindrical three-layer structure of arbitrary thickness made of viscoelastic material. It consists of two external bearing layers and a middle layer, the materials of which are generally different. The problem of nonstationary longitudinal-radial vibrations of such a structure is formulated. Based on the exact solutions in transformations of the three-dimensional problem of the linear theory of viscoelasticity for a circular cylindrical three-layer body, a mathematical model of its nonstationary longitudinal-radial vibrations is developed. Equations are derived that allow, based on the results of solving the vibration equations, to determine the stress-strain state of a cylindrical structure and its layers in arbitrary sections. The results obtained allow for special cases of transition into cylindrical viscoelastic and elastic two-layer structures, as well as into homogeneous single-layer cylindrical structures and round rods.

Optimizing Milling Processes through FEA: An In-depth Analysis of Cutting Tool Geometric Parameters and Their Impact on Performance of milling.

Abstract In the rapidly advancing world of manufacturing, the optimization of cutting processes is of paramount importance for enhancing efficiency and product quality. This work underscores the necessity of employing Finite Element Analysis (FEM) for a comprehensive understanding and improvement of cutting processes. By leveraging DEFORM we create a detailed 2D simulation of the milling process, allowing for an unprecedented inspection of the procedure in a virtual environment. Central to our investigation is the variation of geometric parameters of the cutting tool within the FEM simulation model, offering insights into how minute alterations can significantly affect the outcome of the milling process. The study systematically analyzes the impact of the milling tool’s geometric parameters on various process parameters, including chip formation and cutting forces. This analysis is critical for identifying optimization opportunities in tool design and process settings. Furthermore, we delve into the stress-strain state of the cutting zone, a factor crucial for understanding the material behavior under operational conditions and ensuring the structural integrity of the final product. Through our findings, we demonstrate that strategic modifications in the geometric parameters of the cutting tool can lead to substantial improvements in process performance. This research not only contributes to the body of knowledge on milling processes but also provides practical recommendations for engineers and manufacturers striving to optimize their cutting operations through the application of FEM.

Virtual Modelling of the Stress-Strain State of the Bar Thrust System in the Chrome Plating Technological Process

Abstract Chrome plating of long bars in conventional batch plants proves to be challenging, requiring complex lifting equipment and considerable vertical space. Therefore, the use of continuous chrome plating plants, which allow controlled passage of the bars through the chrome plating bath, is preferred. The continuous hard chrome plating plant operates automatically, controlling the entire process from the loading to the discharge of chrome plated bars. The feed and discharge mechanisms must allow the flow of electric current through the bars subject to the chrome plating. This calls for the design of some mechanisms capable of ensuring a constant feed of bars and their efficient discharge. This paper presents a virtual study using finite element analysis (FEA) focused on the strength assessment of the mechanism including the drive pin, the levers and the sliding plates responsible for the movement of the bars. As a result of the study, essential data on critical stresses, local deformations and factor of safety (FOS) for the whole mechanism were obtained, thus providing valuable information for the optimization of the chrome plating process.

Analytical Overview of the Methods of Controlling the Parameters of Vibratory Compaction of the Concrete Mixes

Introduction. A historical (retrospective) overview of the evolution and application of the methods of concrete mixture compaction by vibration, as well as an overview of the breakthrough scientific+ advancements in the studied field have been presented. The use of the dry concrete mixes that reduce cement consumption, accelerate the strength gain of concrete, reduce the shrinkage strain and heat emission and increase the strength and durability of products has been proposed. The theoretical and practical issues of vibratory compaction of the concrete mixes, the research on the effect reached by the various vibration modes of the vibrating tables, the issues of choosing an efficient mode of vibration impact during compacting the concrete mixes and optimisation of their parameters have been studied. The vibrating table design, the installation layout of the vibrator’s eccentric weights to obtain a given value of the exciting force and the layout of a vibration module with the directed vibrations have been studied in detail. The criteria of duration of the concrete mixture compaction have been defined, changes of the impact parameters during compacting the concrete mixes have been characterised and technical specifications of the vibrating tables have been defined. In the article considerable attention has been paid to the main parameters of the vibrocompacting machines: frequency, amplitude and acceleration of the working member. Most often, the parameter of intensity is used to assess the efficiency of the vibration impact received by the mixture during the compaction process.Materials and Methods. A mixture that turns into concrete after compaction, setting and hardening was selected for the research. The various methods and parameters of concrete mixture compaction to obtain the high-quality concrete were studied. The impact of the various vibration modes on the process of compaction of concrete mixes was investigated, the criteria for the efficient selection and optimisation of the vibration impact parameters were revealed. The paper presents the criteria for assessing duration of the concrete mixture compaction and describes the changes in the parameters during compaction of the concrete mixes. The technical specifications of the vibrating tables of different types and sizes were also presented. The choice of the vibration compaction mode for the concrete mixture is a complicated task, which includes many parameters.Results. Upon the research, the data on the process of concrete mixture compaction under the impact of vibration forces has been obtained. The process results in the destruction of the structural bonds and weakening the bonds between the particles, which leads to the emergence of a variable stress-strain condition. It has also been found that under such settings, the mineral particles get transferred and a denser packing is formed.Discussion and Conclusion. The resulting denser packing of the concrete mixture particles ensures the undoubted economic advantage due to reduced consumption of a binder without loss of the strength properties of concrete.

Stress-strain state of dental immediate prosthesis and associated tissue under the influence of external force

Purpose: to analyze the stress-strain state (SSS) of a removable plate immediate denture with a printed dentition made of polymethyl methacrylate (PMMA) and a polyethylene terephthalate (PET) base under multifactor loading conditions based on the principles of mathematical modeling. Materials and methods: For mathematical modeling of SSS, Comsol Multiphysics 5.6 software (Comsol Inc., USA) was used, which provided numerical data for analytical interpretation. We considered a flat 2D model consisting of a printed monolithic dentition and a PMMA bonding layer, a PET base, the mucous membrane of the prosthetic field and jaw bone tissue. Results: The fields of von Mises stresses (VM) and deformations under the influence of normal, oblique and tangential loads (up to 500 N), the localization of their maximum values and the average value inside the prosthetic structure, mucous membrane and bone tissue were determined. The maximum values of VM in the mucous membrane are compared with the pain threshold based on known literature data on algesiometry of the oral mucosa. An assessment was made of the critical length of microcracks (CLM) according to Griffiths, which lead to the formation of a main crack followed by brittle fracture of the structure base. Using the phase field method, the probability of crack formation in the considered model of an orthopedic structure under the influence of static loads of various magnitudes and directions was calculated. Conclusions: Using the method of mathematical modeling of SSS, it was shown that failures when using immediate dentures with printed teeth made of PMMA and a PET base can be caused by the effect of overloading the areas of the base and caused by the deformation process inside the prosthetic structure. The maximum stress in the prosthetic elements was 79.7 MPa and deformation – 0.47 mm. The pain threshold of the oral mucosa is higher than the highest stress value in the prosthetic bed according to Mises (0.002 MPa) for normal load of 500 N. The SSS heterogeneity coefficient of the removable plate immediate prosthesis model is 8.6. The critical length of a microcrack according to Griffiths is lcrit = 1.9...2.7 µm. Using the Comsol Multiphysics phase field method, it was established that the probability of the formation of a large crack in the base of the prosthesis was 6·10–3 %, 0.36 %,0.73 % for a normal, inclined and shear load of 500 N, which is a sufficient value for the operation of removable laminar dentures with printed teeth from PMMA and a PET base during the warranty period.

Experimental studies of the influence of deformations in nodal joints on the stress-strain state in a full-scale support made of MIC-C

Experimental studies of the influence of deformations in nodal joints on the stress-strain state in a full-scale support made of MIC-C

CALCULATION OF FLAT SHELLS BY THE BOUNDARY ELEMENT METHOD

This article describes the iterative process of solving the problem of the stress-strain state of a long flexible cylindrical panel. Stress-strain state and the study of the stability of flat shells taking into account the physical, mechanical properties of the material, the process of deformation change. It is based on sequential approximation methods and the boundary element method (MGE). The results of algorithmic weighting are presented in the form of a table showing what value each band represents. The equations are determined by solving twelve unknown values of functions at the ends of the segment. Linear problems of elasticity theory and plate theory fundamental solutions have a simple form, so the method is widely used here. For flat shells, the matrix of fundamental solutions is determined by complex volumetric expressions, and for flat shells - by special functions. Therefore, there is little research on solving problems in the theory of flat shells by the boundary element method. In this regard, an urgent topic of research is the development of methods of boundary integral equations for solving linear and nonlinear problems in the theory of flat shells based on the application of fundamental solutions defined by simple analytical expressions. The scientific novelty of the work consists in the development of a methodology for assessing the reliability of thin-walled spatial structures using the boundary element method.

COMPUTER SIMULATION OF THE STRESS-STRAIN STATE OF BAR BLANKS MADE OF ALLOY 7075

The article presents a study of the characteristics and technological parameters of bar blanks made of aluminum alloy 7075, depending on the temperature and the forming process. The main goal is to determine the stress-strain state at various temperatures during the production of blanks, which contributes to understanding the mechanism of formation of the structure and properties of bar blanks. To do this, a computer simulation of the process based on the finite element method is used, using the Forge3D software environment. The results obtained confirm the uneven structure in the volume of workpieces, with a pronounced intensity of deformation in the surface layers. The formation of workpieces at different temperatures (200 and 250 °C) showed differences in stress intensity and strain rate, which is important for understanding the processes of formation of microstructure and material properties. Special attention is paid to the influence of temperature on the formation of stresses in the rods, as well as their distribution in thickness and length. The results obtained can be used to optimize the technological parameters of the aluminum alloy forming process in order to improve the quality of the final product and production efficiency. In general, the scientific conclusions of this study contribute to the further development of aluminum alloy processing technologies and their application in various industries. Keywords: computer modeling, finite element method, numerical model, processing technology, Forge3D, deformation characteristics, microstructure formation process.