Complex Stress-strain State Research Articles

Analysis of the stress-deformed state of the structure of road clothing depending on the location of the load relative to the edges of the combined slab

Abstract. Problem. Cement-concrete coatings are characterized by the complexity of repair work, therefore, for their repair or new construction, it is advisable to use asphalt-concrete coating. This constructive solution during the repair of cement concrete slabs helps to improve their technical and operational condition since the asphalt concrete layer performs the function of a protective or wearresistant layer on cement concrete slabs. The operating conditions of asphalt concrete layers on cement concrete slabs are significantly different from those typical for other structural solutions. The existing methods of calculating the strength of asphalt concrete coatings for hard road wear are not accurate enough, because they take into account only certain criteria of the strength of the asphalt concrete layer. The specifics of the stress-strain state of the asphalt concrete layer on cement concrete slabs under different load conditions, such as the middle of the slab, the edge of the slab, and the corner of the slab, are not taken into account. Given the complex stressstrain state of the asphalt concrete layer on a rigid base, the analysis of the stress-strain state is particularly relevant, aimed at determining the most dangerous variant of the location of the transport load to ensure the strength of the asphalt concrete layer. Goal. The purpose of this article is to determine the stress-deformed state of an asphalt concrete layer on a rigid base with various options for applying a transport load, which will allow the establishment of the most dangerous option for the location of the load. Methodology. General methods of solving problems of the mechanics of a deformed solid body were used to develop a calculation scheme and select a material model. Simulation of the stress-strain state of the road surface was carried out using the finite element method using the ANSYS software complex, investigating three options for placing the transport load: in the center of the slab, on its edge, and in the corner. Results. According to the results of the simulation of the stress-strain state of a combined slab made of an asphalt concrete layer on a rigid base, it was established that the edge of the slab is the most unsafe both in terms of tensile and shear stresses for a cement concrete slab. For the asphalt concrete layer, placing the load in the corner of the slab is the most dangerous both in terms of tangential shear stresses and Mises stresses. Originality. According to the results of the simulation of the stress-strain state of a combined slab made of an asphalt concrete layer on a rigid base, it was established that the edge of the slab is the most unsafe both in terms of tensile and shear stresses for a cement concrete slab. Practical value. Based on the results of modeling the stress-strain state of a combined slab made of an asphalt concrete layer on a rigid base, it was established that the edge of the slab is the most dangerous both in terms of tensile and shear stresses for a cement concrete slab. For the asphalt concrete layer, placing the load in the corner of the slab is the most dangerous both in terms of tangential shear stresses and Mises stresses

INCREASING THE EFFECTIVENESS OF CIVIL PROTECTION BY THE DESIGN OPTIMIZING: THE REVIEW

Due to today's conditions, it is necessary to reconsider the purpose of buildings and structures that use a significant number of reinforced concrete elements subjected to complex stress-strain states. The researchers are faced with the task of determining the residual bearing capacity of an element with uneven damage, which will allow choosing the most optimal option for calculating and selecting materials. A detailed analysis of the most common damages to reinforced concrete structures, including protective structures and shelters, from the effects of explosives and weapons of various types was carried out to optimize and maintain strength and durability. It is also important to study the impact of damage that causes a stress-strain state that cannot be predicted by calculation.

Physico-mechanical Characteristics of the Diaphragms of a Diaphragm Piston Pump Made of Polyurethane Compound

The results of the bench tests of the diaphragms of diaphragm piston pumps made of composite materials based on twocomponent polyurethane filled with basalt fiber are presented. The tests were carried out using a tensile testing machine equipped with special equipment that allows simulating a complex stress-strain state in the diaphragm which is characteristic of pump operation in the real conditions. According to the results of the tests the diaphragms with a basalt content of 1 and 2 vol. % showed the greatest resistance to mechanical loads.

Stability of a reinforced concrete column under compression with torsion caused by accidental action

Under emergency situations associated with sudden failures of the load-bearing elements of the structure, torques may additionally occur in the columns due to the specifics of the structural design of the buildings. Thus, the columns may be in a complex stress-strain state. The objective of this study was to develop a semi-analytical design model for analysis of the stability of reinforced concrete columns subjected to compression with torsion as a result of an accidental action. For achieving the objective, authors formulated the initial hypotheses, developed the determining equations for calculating the stability of a reinforced concrete column subjected to compression with torsion. To validate the reliability of the proposed model, it has been compared with the results of modeling in the software complex Ansys. Analysis of the data showed that the largest difference between the results was up to 8.08% for the case P = 0.4·Pcr,e = 126.6 kN. The smallest difference of 3.6% was for the case P = 0.9·Pcr,e = 284.85 kN. It has been shown that as the torque increases, there is a decrease in the value of the critical force causing loss of stability. This is due both to the action of the torsional pair of forces during the distortion of the rod and to the decrease in the mechanical properties of concrete under the combined action of normal and tangential stresses.

Probabilistic notch fatigue assessment under size effect using micromechanics-based critical distance theory

Geometrical discontinuities are inevitable in engineering structures due to various functional requirements, which often yield complex stress–strain state and thereby significantly impact their fatigue performances. In this study, crystal plasticity theory is coupled with traditional critical distance theory for notch effect modelling considering microstructural heterogeneity. Specifically, microstructural and geometrical size effects on critical distance and fatigue performance are studied based on Sub-modelling approach. In addition, critical distance theory is coupled with Weibull distribution for probabilistic fatigue life evaluation of notched components. The developed method is verified and compared by using experimental data of GH4169 alloy. The findings demonstrate that the evaluated P-S-N curves exhibit strong agreement with tested data and geometrical size effect poses larger influence than the grain size effect on critical distance and fatigue life.

MODELING OF STRESS-STRAIN STATE AND STRENGTH OF DAMAGED CONCRETE BEAMS REINFORCED WITH CARBON FIBER FABRIC IN PC "LIRA-SAPR"

The study examines the problem of preserving and improving the architectural heritage in Ukraine. Many buildings and structures have a long service life or are already deteriorating due to their age and other factors. This is particularly true for reinforced concrete structures, which often have various defects and damage. Unfortunately, there are no clear methods for assessing the residual load-bearing capacity of such structures. However, the research indicates that the residual potential of damaged elements may be significantly underestimated. Therefore, it is crucial to explore and apply effective innovative solutions for strengthening these constructions. One such solution involves using composite materials (fiber-reinforced polymers, FRP) for external reinforcement of structures. Composite materials offer numerous advantages, including high strength, low weight, resistance to aggressive environments, and durability. The article presents the results of a numerical experiment aimed at investigating the influence of damage and reinforcement with carbon fiber-reinforced polymer (CFRP) on the stress-strain state and residual load-bearing capacity of concrete beams with basalt-plastic reinforcement (BFRP). For the experiment, 15 rectangular beams with dimensions of 2000×200×100 mm were prepared and nonlinearly analyzed using the "LIRA-SAPR" software, which employs the finite element method. The data obtained for each beam were compared with the results of laboratory tests, revealing that CFRP reinforcement increases the residual load-bearing capacity of the beams without significantly affecting their working deformation. Additionally, a comparative analysis was conducted on the residual load-bearing capacity and stress-strain state of the beam components: CFRP fabric, concrete, and reinforcement. The authors assert that modeling the complex stress-strain state of experimental basalt-concrete beams using nonlinear finite element calculations through the "LIRA-SAPR" software accurately reproduces experimental results, provides insight into the most likely failure mode, and reliably predicts their load-bearing capacity.

EXPERIMENTAL EVALUATION OF THE STRUCTURAL INTEGRITY OF VERTICAL CYLINDRICAL STORAGE TANK SHELL-TO-BOTTOM JOINTS OF VARIOUS DESIGNS

Bottom-to-shell joint is one of the most critical areas in vertical cylindrical storage tanks, both in terms of the number of detected flaws and the causes of failures. The primary factors contributing to the present state include the structural peculiarities of the shell-to-bottom joint, leading to incomplete fusion in the middle between the double filletgroove welds (double fillet welds) and, consequently, low inspectability. This results in a complex stress-strain state with maximum stress levels in the area of the shell-to-bottom joint. Thus, improving the existing design of the bottom-to-shell joint is relevant.This article presents the results of comparative resource evaluation tests conducted on the typical design of the shell-to-bottom joint and two prospective designs: one with complete penetration weld and another with a T-section. The tests were conducted using prototypes that replicate the necessary structural properties of the shell-to-bottom joint and the stress distribution diagram, allowing testing on standard servo-hydraulic machines. The results obtained indicate that all considered designs of shell-to-bottom joints, when free from flaws, exhibit high reliability, ensuring safe operation even under double the operational stresses for a minimum of 50 years. Considering the improved inspectability and feasibility of manufacturing these prospective shell-to-bottom joint designs, along with their comparable production costs, they can be recommended for practical applications.

In-situ investigation on indentation response at subsurface by multi-detector inside SEM

Indentation tests create complex stress–strain states in the region beneath the indentation tip. However, it is difficult to observe the indentation responses of bulk materials. Therefore, this study presents a wedge-indentation test technology that can investigate the subsurface deformation behavior during loading and unloading inside a scanning electron microscope. In situ observations based on multiple techniques, including a secondary electron detector, electron backscatter diffraction, and digital image correlation, are realized and used to investigate the texture evolution and stress–strain behavior of monocrystalline copper in the microregion beneath the indentation tip. Indentation induces kinked slip bands along the [01‾1‾] and [011‾] directions. The maximum shear strain of 0.324 occurs at the sides of the area in direct contact with the indentation tip. The lattice rotations in three dimensions are calculated and obtained quantitatively, and the geometrically necessary dislocation density beside the contact region reaches 0.70 × 1014/m2. The proposed method has considerable potential for explaining the deformation mechanisms of materials at microscale.

Stress-strain state during the formation of normal cracks in three-layer bendable reinforced concrete elements under the action of longitudinal and transverse forces

Most wall panels in operating multi-storey residential buildings are in a complex stress-strain state under the influence of vertical and horizontal loads, such as their own weight, wind, etc. These features must be taken into account in the calculation in order to ensure operational safety. The combination of vertical and horizontal forces acting simultaneously for three-layer bending elements leads to the fact that the boundary between the compressed and tensile zones not only moves from one layer to another, but also has a different geometric shape depending on the ratio between the vertical and horizontal load. The stress-strain state during the formation of normal cracks in three-layer bendable reinforced concrete elements is caused by the impact on layers of different concretes. The formation of normal cracks occurs due to the achievement of ultimate tensile strength by the most stretched concrete under the influence of external loads. Since three-layer reinforced concrete elements consist of two outer layers (reinforced concrete) and a middle layer (lightweight concrete), when such an element bends, the outer layers are subject to compression, and the middle layer is subject to tension. The boundary of the compressed zone can be located either in one of the outer layers or intersect the middle layer, which falls into both the compressed and stretched zones. To analyze the stress-strain state during the formation of normal cracks, it is necessary to take into account the fol-lowing parameters: geometric characteristics of the element (dimensions and shape of the section, layer thickness, etc.), physical and mechanical properties of concrete (compressive and tensile strength, elastic modulus, Poisson's ratio, crack resistance coefficient, etc.), characteristics of reinforcement (class, diameter, pitch of bars, etc.) and its location in the section.

Test results of diaphragm piston pump made of composite material based on polyurethane compound

The paper presents the results of bench tests of diaphragm membrane-piston pumps made of composite materials based on two- component polyurethane. The tests were carried out with the help of a rupture machine, equipped with special equipment, which allows to imitate the complex stress-strain state in the diaphragm, which is characteristic of the operation of pumps in real conditions. According to the results of the tests, the diaphragm with the content of basalt is 1 and 2 ob. % showed the same ultimate strength.

ELASTIC-PLASTIC DEFORMATION OF STEEL-CONCRETE BEAMS WITH LOCAL CRUMPLING DURING THREE-POINT BENDING

The study presents the results of experimental modeling of elastoplastic deformation of bent massive concrete filled steel tube beams under three-point bending. It has been shown that local deformations and local crushing in such structures have a significant impact on their behavior. The applicability of the theory of bending of a hollow steel beam according to the Bernoulli model is analyzed. A comparison has been made of the bearing capacity and stress-strain state of hollow steel tubes (according to the Bernoulli model and the results of experiments) and concrete filled steel tube beams, and the contribution of the concrete core to the bending resistance during elastoplastic deformation has been quantitatively assessed. The actual load-bearing capacity of a hollow pipe during three-point bending does not exceed 50% of the calculated theoretically determined one, which indicates the impossibility of using the classical bending model when designing systems of this kind. In this case, the concrete filled steel tube beam not only ensures the full functioning of the metal during the deformation process, preventing its disruption, but also provides some increase in load-bearing capacity due to the inclusion of a compressed zone in the concrete work. The increase in the load-bearing capacity of a beam due to the introduction of a concrete core can reach 70%. Despite their significant weight, bendable tube-concrete rods can be recommended in conditions of a complex stress-strain state, in which, in addition to transverse bending loads, significant longitudinal forces arise, as well as local force factors that contribute to the occurrence of local crushing deformations, since, unlike a thin-walled hollow tube, concrete the core significantly prevents these effects. Based on the results of the study, the potential effectiveness of flexible tube-concrete elements for a number of structures was proven.

Analysis of the influence of anchor piles on test results

The paper considers the main problems of design and calculation of deep foundations of high-rise buildings in the form of piles-barrettes. The results and methodology of field tests of barrette piles for the foundation of a 56-storey residential building in Moscow are presented. The characteristics of engineering-geological conditions of the future construction site and design solutions for pilot tests are presented. Given a large cross-section of the barrette, which involves a significant amount of pile-type soil mass with the formation of a complex stress-strain state, to obtain reliable results and verification of the calculated model is recommended to perform numerical tests in full compliance with the field experiment, taking into account the anchored piles. The paper describes the method and the results of the numerical calculation of the load-carrying capacity of a barrette taking into consideration the modeling of an anchoring system in the Midas GTS NX program complex by the finite-element method and shows the basic possibility of using the program complex and the described method for practical purposes with an admissible accuracy. The paper contains diagrams of vertical displacements of a barrette head as a function of the applied load in full-scale tests and a general evaluation of the carrying capacity of a barrette pile obtained by numerical solutions. It is found that by taking into account the anchoring system (beams and piles) in the numerical simulation, the calculation results obtained are the most accurate to the field tests in describing the behavior of the pile under load in comparison with the calculation of a single barrette pile. In spite of the fact that the barrette bottom is embedded into the rocky soils, the barrette piles are referred to the hanging piles according to the interaction conditions with the soil due to the significant load transfer along the lateral surface.

Strength and deformity of the osteosynthesis system of a damaged upper jaw with orthodontic apparatus

Mathematical modeling was used to determine the stress-strain state of the developed simulation model of the biomechanical system "Orthodontic appliance – maxilla". The patterns of changes in the stress state were determined and the values of deformation displacements in the structural elements of the biomechanical system were determined under a force stress of the orthodontic device with an amplitude of 50 N. The strength and strain changes of the mutual location of unfused maxillary fragments and the orthodontic appliance of a given type were evaluated using the data of a numerical experiment. Simulation computer modeling of the stress-strain state of the system showed that activation of the kinematic mechanism of the appliance with a force of 50 N causes the emergence of a complex stress-strain state of midface bones, which contain tensile, compressive, shear and torsion deformations. Equivalent von Mises stresses in the maxillary bone tissue are distributed unevenly. When the orthodontic appliance is activated, there is an asymmetry in the distribution of stresses between the right and left sides both for the appliance itself and for the maxillary bone tissue. When the appliance is activated with a force of 50 N, the stresses in the base of the appliance and bone tissue do not exceed the maximum permissible values.

Process Pipeline Strength Calculation Methodology Enhancement Using Finite-Element Method

The paper analyzes possible approaches to the technical evaluation of the process pipelines according to the diagnostic results using strength calculation based on the finite-element method. Process pipelines have a complex dimensional configuration and a complex stress–strain state, so traditional approaches to technical diagnostics and assessment of the technical condition of main pipelines are not applicable. Qualities of the process pipelines as objects bring relevance to the development of the practical approaches to its numerical modeling and formalization of boundary and loading conditions when using software systems based on the finite-element method. This paper presents the results of experimental studies of the stress–strain state of a number of test benches simulating elements of pipeline structures. Therefore, analytical research is presented that allows recommendations to be formulated for the numerical modeling of the process pipelines. The formulated recommendations allow us to correctly simulate process pipelines when calculating their stress–strain state using the finite-element method to model the conditions of fastening and loading, thereby ensuring high accuracy of the assessment of the technical condition of structures based on the results of their diagnostics.

Mathematical modelling of stress-strain state of steel-concrete beams with combined reinforcement

Abstract Most of the modern computer software for the building structures‘ calculation is based on mathematical dependencies which make it possible to analyse rather complex stress-strain state of structures subjected to loading. As a rule, the calculation is based on the finite element method and is reduced to the calculation of deformations arising in structures due to the action of external forces with the use of real strain diagrams of materials, σ-ε diagrams for concrete and reinforcement. Modern normative regulations for reinforced concrete structures‘ calculation are also based on the deformation model using material deformation diagrams, which are as close to the real ones, as possible. Therefore, this study was aimed to investigate in more detail the stress-strain state and the physical essence of the processes occurring in reinforced concrete structures with combined reinforcement according to mathematical approaches and regulations of DBN B.2.6-98:2009 and DSTU B. In 2.6-156:2010. Namely, in the research is analysed the combined reinforcement of S245 steel tapes and A1000 rebar, which is used in the production of reinforced concrete elements. The results of mathematical modelling were compared with the calculation results, according to DBN B.2.6-98: 2009 and DSTU B. B 2.6-156:2010, as well as with field experimental data. Therefore, the conclusion could be made, whether it is possible to use this technique with sufficient accuracy to calculate reinforced concrete structures with combined reinforcement.

Criteria for opening an axial cavity in cross-wedge rolling

The application of empirical, phenomenological deformation and energy theories of metal fracture in relation to the process of cross-wedge rolling is considered. A distinctive feature of cross-wedge rolling in comparison with other metal pressure treatment processes is the complex stress-strain state in the deformation focus and the possibility of opening the axial cavity. The existing empirical criteria of destruction are given. The scheme of a new calibration test based on crosswedge rolling and the fracture criterion proposed by Zbigniew Pater are considered. It is shown that the Zbigniew Pater’s empirical criterion for the destruction of Zbigniew Pater provides a correct determination of the moment of opening the cavity during cross-wedge rolling. The improved phenomenological deformation theory is based on the theory of fracture developed by V. L. Kolmogorov. It is proposed to evaluate the plasticity of the metal depending on the stress state in the form of two independent invariants of the stress tensor: the average stress and the parameter of the third invariant of the stress tensor. The dependence of the limit value of accumulated deformation, at which destruction occurs, on the stress state is constructed in the form of a plasticity surface. The phenomenological deformation criterion of metal destruction during plastic deformations allows us to determine the moment of opening the cavity during cross-wedge rolling and the plasticity resource of the metal.

Analiza uzroka loma magistralnog gasovoda

A complex of research has been conducted to establish the causes of the accident of the main gas pipeline made of 1420x15.7 mm X70 steel after 20 years of operation. It is found that pipe destruction was initiated by the longitudinal crack with a length of 470 mm and a maximum depth of 6.8 mm, oriented in the direction of the pipe and perpendicular to the outer surface of the pipe identified as stress-corrosion cracking. The crack initiation is due to the disboundment of the tape protection coating, the high corrosion activity of the soil, and the complex stress-strain state caused by deviations from the design objectives during construction. The chemical composition the base metal of all investigated pipes corresponds to the requirements of the technical conditions for steel pipes in category X70; pipes welding are performed with the typical materials used in pipe welding plants. Despite the differences, the structural and mechanical characteristics (yield strength, ultimate strength, and impact strength) of the steel and weld metal of the studied pipes are identical. The relative elongation (d5) of the operated pipes is below the normalized values, but, it is necessary to take into account the possibility of deviations in these characteristics of steel in the initial state. Significant reserves of toughness indirectly indicate low damage of metal and, accordingly, satisfactory resistance to destruction of the metal of the studied pipes.

STUDY OF THE STRESS-STRAIN STATE OF THE MAXILLA DURING ORTHODONTIC TREATMENT OF DENTOGNATHIC DEFORMATIONS IN CHILDREN WITH CONGENITAL CLEFT LIP AND PALATE.

The aim: To create a three-dimensional simulation mechanical-mathematical model of the biomechanical system "Orthodontic appliance-maxilla", to study peculiarities of the stress-strained state of the maxilla. Materials and methods: A simulation model of the biomechanical system "Orthodontic appliance-maxilla" was created using computed tomography (CBCT) data. Mathematical modeling was used to determine the stress-strain state of the simulation model. Results: The patterns of changes in the stress state were determined and the values of deformation displacements in the structural elements of the biome-chanical system "Orthodontic appliance-maxilla" were determined under a force stress of the orthodontic device with an amplitude of 50 N. Conclusions: Simulation computer modeling of the stress-strain state of the "Orthodontic appliance-maxilla" system showed that activation of the kinematic mechanism of the appliance with a force of 50 N causes the emergence of a complex stress-strain state of bones. When the orthodontic appliance is activated, there is an asymmetry in the distribution of stresses by Mises between the right and left sides both for the appliance itself and for the maxillary bone tissue.

Analysis of multiaxial fatigue models based on the results of biaxial tests for aluminum alloys

During operation, modern structures and their parts are subjected to complex cyclic loads. In this case, a complex stress-strain state can arise in products, which can lead to a significant decrease in their fatigue life. In this regard, the development of methods for predicting fatigue fracture of critical structures becomes urgent. The purpose of this work is to test a simple approach for describing multiaxial fatigue datasets presented in the literature and compare it with known multiaxial fatigue models. Within the framework of the study, actual experimental data was considered, containing experimental data on the multiaxial fatigue of aluminum alloys 2024-T3 and 2024-T4. The alloys are actively used in the designs of aircraft, ships and spacecraft. As a result, the Sines model and its modernized version were considered (taking into account the first invariant of the stress tensor with respect to amplitude values). At the same time, an approach was developed to determine the constants of the models based on the results of two variants of training experiments. The paper presents the results in the form of relationships of the predicted and experimental fatigue life, obtained using the Sines model and its modification for two types of training tests. In the final part of the work, a comparative analysis of the Sines model and its modification, Smith-Watson-Topper, Fatemi-Socie and its modification is carried out. The analysis showed that the modified Sines model significantly improves the predictive ability, the proposed model better described the experimental data than the traditional Sines model and the Smith-Watson-Topper approach. At the same time, the descriptive ability of the model is comparable to the Fatemi-Socie one.

ПРЕДВАРИТЕЛЬНОЕ ОПИСАНИЕ РАБОТЫ ЖЕЛЕЗОБЕТОННЫХ ЭЛЕМЕНТОВ С ВНЕШНИМ АРМИРОВАНИЕМ КОМПОЗИТНЫМИ МАТЕРИАЛАМИ ПРИ ИЗГИБЕ С КРУЧЕНИЕМ

The calculation methods of reinforced external reinforcement elements when working on torsion are considered succinctly in available sources and current regulatory documents. This article discusses a number of existing proven methods for calculating reinforced concrete bendable elements with external composite reinforcement, including when working with torsion. The necessity of introducing into the existing calculation dependences of the prerequisites for substantiating the behavior of reinforced concrete bendable elements, including those with external composite reinforcement, when working in a complex stress-strain state is described. The cases of occurrence of additional torsional forces in the conditions of classical variants of loads and impacts on the element are considered. A description of the work of reinforced concrete elements with external reinforcement with composite materials during bending with torsion is proposed. The main provisions of the work of reinforced concrete structures in bending with torsion are given. The main limiting states are presented. An assumptions are made about the possible presence of additional limiting states of reinforced concrete elements with external reinforcement with composite materials. A variant of the condition of proportionality of longitudinal relative deformations for reinforced concrete elements with external reinforcement with composite materials during bending with torsion is proposed.