Characteristics Of Crack Resistance Research Articles

Fracture characteristics of SMA mixtures with hydrated lime through the semi-circular bending approach

Stone Mastic Asphalt (SMA) is a composite mixture made up of high-quality crushed stone, fine aggregates, an asphalt binder, and a significant percentage of mineral filler in contrast to conventional mixtures. Renowned for its durability and rolling resistance, it is predominantly employed as a surface “wearing” course on main roads subjected to heavy traffic, but it can also be used as a binder course under specific project requirements. In this study, we investigated the effect of hydrated lime as a partial replacement of limestone filler at various concentrations on the mechanical and cracking resistance characteristics of 10-mm SMA mixtures. The semi-circular bending (SCB) test, which is pivotal for understanding the cracking mechanism was used to assess the mixtures performance-related response to this distress type. The mixture cores were produced with granite aggregates, limestone filler as natural filler, hydrated lime as natural filler replacement, and a 30/45 penetration asphalt type. Mixtures containing 1.1 %, 2.2 %, and 3.4 % of hydrated lime by weight of aggregates were evaluated, in addition to a control mixture without hydrated lime. The factors considered for comparing the mixtures included: load and deformation curves, stiffness, fracture toughness, fracture energy, and flexibility index of the mixtures. The experimental program also comprised a set of various test temperatures (0°C, 10°C, and 20°C) to better understand the cracking mechanism. Experimental results indicated a significant performance-dependency on the HL concentration and the test temperature. Precisely, it was found that the mixture with the highest hydrated lime content (3.4 %) exhibited the best cracking performance at 0°C and 20°C, making it a suitable filler replacement concentration. However, at 10°C, the mixture containing 2.2 % hydrated lime showed the most consistent performance overall, suggesting and important improvement in asphalt mixtures’ cracking resistance. Overall, these findings obtained from the SCB test approach substantiate the potential benefit of hydrated lime filler replacement in optimizing the cracking performance and durability of SMA mixtures under varying temperature conditions and loading regimes.

Improving Environmental Stress Cracking Resistance of High-Density Polyethylene Grades by Comonomer Addition and Nanocomposite Approach.

The aim of this paper is to determine the effect of polymer density, correlated to the comonomer content, and nanosilica addition on the mechanical and Environmental Stress Cracking Resistance (ESCR) characteristics of high-density polyethylene (HDPE). In this regard, five HDPE samples with similar Melt Flow Index (MFI) and molar mass but various densities were acquired from a petrochemical plant. Two polymerization reactors work in series and differ only in the amount of 1-buene comonomer fed to the second reactor. To ascertain the microstructure of the studied samples, GPC and SSA (successive self-nucleation and annealing) analyses were accomplished. All samples resulted having similar characteristics but slightly various SCB/1000 C=7.26-9.74 (SCB=Short Chain Branching). Consequently, meanwhile studied HDPEs reveal similar notched impact and stress at yield values, the tensile modulus, stress-at-break, and elongation-at-break tend to demonstrate different results with the SCB content. More significantly, ESCR characteristic varied considerably with SCB/1000 C extent, so that higher amount of SCB acknowledged advanced ESCR. Notably, blending HDPE sample containing higher amount of SCB/1000 C, with 3 wt.% of chemically modified nanosilica enhanced ESCR characteristic by 40 %. DFT (Density Functional Theory) calculations unveiled the role of the comonomer, quantitatively by binding energies and qualitatively by Non Covalent Interaction (NCI) plots.

RESEARCH OF THE STRESS-STRAIN STATE OF PRECAST REINFORCED CONCRETE HOLLOW CORE SLABS UNDER THE ACTION OF A CONCENTRATED AND UNIFORMLY DISTRIBUTED LOAD

The scientific work is devoted to a comprehensive study of the stress-strain state of prefabricated hollow-core floor slabs, establishing the nature of deformation, as well as determining the characteristics of crack resistance, deformability and load-bearing capacity experimentally under short-term loads. The experimental data obtained were confirmed by theoretical calculations. The scientific novelty of the experiments carried out within the framework of the presented work lies in the improvement of the principles of direct design of floor slabs from commercially produced beam slabs, the possibility of determining the stress-strain behavior of a slab structure using the formed ends. The method of monitoring the stressed behavior of a slab structure was also further developed. For the first time, the results of full-scale experimental studies of the stress-strain behavior of a prefabricated slab, carried out using the hydraulic loading method, have been obtained, and the features of the deformation of a slab embedded in the wall of a multi-story building have been experimentally established. The article provides recommendations for the practical use of the research results obtained, and also develops technical specifications for the production of concrete slabs during design and construction. The developed proposals were used in the construction of residential buildings in Kharkiv. When using the recommended grade of concrete C25/30 (instead of the actual grade C20/25 tested), the rigidity of the slab increases and its deflections will be smaller. Based on the data obtained from the experimental testing of the slabs, a generally positive test result should be stated. During further serial production of slabs, periodic testing of batches of slabs should be carried out in accordance with DSTU B V.2.6-53:2008. In this case, the slabs are accepted according to the indicators of strength, rigidity, crack resistance, fire resistance limits, frost resistance limits, as well as water resistance of slabs intended for use in aggressive environments. Keywords: concentrated load, testing, concrete, calculation, deflection, transverse force.

Strength Indicators of Fiber Reinforced Concrete with Carbon Nanomaterials

Concrete composites with low defects, dense and homogeneous, with a high degree of adhesion between the cement matrix and aggregates, as well as a high ratio between static tensile and compressive strengths and plasticity have the best crack resistance characteristics. This ratio increases in the case of the use of fiber-reinforced concrete. Modern research in nanotechnology focuses on the management of matter at the nanoscale level, which makes it possible to create materials with new properties. Due to the high aspect ratio, flexibility, high strength and rigidity, carbon nanotubes (CNTs) exhibit reinforcing properties. Due to their nanoscale features, CNTs interact with a complex network of calcium-silicate-hydrate binder (C – S – H), contribute to a decrease in porosity and compaction of the cement stone structure, increase the shear forces of matrix adhesion in the contact zone. Thus, there are all prerequisites to assert that fiber concrete with a cement matrix modified with carbon nanotubes will have the required high strength characteristics and crack resistance due to multilevel dispersed reinforcement and the efficient operation of fiber in a nanomodified concrete matrix. This article presents the results of testing samples made of cement stone, concrete and fiber concrete with carbon nanotubes. The presence of carbon nanotubes in cement stone contributes to an increase in compressive strength by 11 %, tensile strength during bending by 20 %. The test results of samples made of reinforced fiber concrete modified with nanocarbon materials have shown an increase in tensile strength during bending up to 109 %, tensile strength during splitting up to 82 %, axial tensile strength up to 78 %.

Numerical simulation analysis of sleeper damage under dynamic load based on discrete element method

To analyze the damage development of concrete sleepers during railway operation, the discrete element method and the parallel bond degradation model are introduced into the damage analysis of concrete sleepers for the first time. The cracking resistance and dynamic characteristics of the sleeper model are verified by comparing the existing literature. The influence of load and the stiffness of the bottom support on the damage development of the sleeper is considered and the following conclusions are drawn: with the increase in the load amplitude, the damage of the sleeper will increase nonlinearly; under the conditions of the same time and the same load amplitude, the number of cracks of the sleeper will increase with the increase of load frequency, and increase exponentially with the number of loads. Different support stiffness at the bottom of the sleeper will change the dynamic characteristics of the sleeper under load, thus changing the damage development of the sleeper. For the sleeper with full support at the bottom, when the support stiffness at the bottom is low, the center of the sleeper is more likely to be damaged. When the support stiffness at the bottom of the sleeper is large, hanging the center of the sleeper about 1/3 of the length of the sleeper can reduce the damage to the center of the sleeper. The research results show that this method can be applied to the study of sleeper damage and provide a new idea for the structural damage of sleepers.

О возможности локального измерения трещиностойкости конструкционных сталей с привязкой к структуре

The scale of heterogeneity of the structures of steels and alloys can be rather large both within one sample and within a product. The procedure adopted in practice for determining the integral values of crack resistance characteristics cannot always reflect this circumstance. In this regard, it is necessary to develop methods for assessing the crack resistance of a medium with a heterogeneous structure. In this work, the authors determined the crack resistance of large forgings made of heat-hardenable 38KhN3MFA-Sh steel (0.38%C–Cr–3%Ni–Mo–V) based on the critical crack opening δс and the J-integral. The presence of critical stages in the development of a ductile crack during testing was assessed by acoustic emission measurements. In combination with the obtained methods of digital fractography of 3D images of fractures, this allowed relating the shape and position of the leading edge of each crack jump to the load-displacement diagram. Measuring the crack opening geometry during the test showed the possibility of determining directly the coefficient of crack face rotation when estimating δс. In general, this allowed constructing a map of the distribution of parameter δс values over the thickness of the sample and estimating the scale of the scatter in crack resistance within one sample – up to 30 %. Such a localization of measurements, primarily of the δc parameter, is comparable to the scale of heterogeneity in the morphology of various types of structures, which was assessed based on the measurement of digital images of the dendritic structure, the Bauman sulfur print, non-metallic inclusions on an unetched section, and ferrite-pearlite banding in the microstructure. This makes it possible to link local crack resistance values to various fracture mechanisms and their accompanying structural components.

Structure and Crack Resistance of Maraging Steels under Single Loading

Abstract—The effect of structural parameters on the strength and crack resistance of maraging steels under single loading has been studied. It has been established that the increase in strength due to dispersion hardening with intermetallic compounds in the studied steels is determined by the titanium content and the presence of cobalt. It was shown that the change in crack resistance under single loading with increasing tempering temperature has a complex character. It has been established that, in contrast to dynamic crack resistance, the minimum level of static crack resistance characteristics of the studied steels corresponds to the maximum strength. Possible reasons for such a change in the characteristics of static and dynamic crack resistance are discussed.

Research and Development of Self-Waterproofing Concrete for Tunnel Lining Structure and Its Impermeability and Crack Resistance Characteristics.

This research paper systematically investigates the combined influence of fly ash, cementitious capillary crystalline waterproofing (CCCW) materials, and polypropylene fibers on the mechanical properties and impermeability of concrete through comprehensive orthogonal tests. Microscopic morphological changes in the concrete induced by different composite materials are examined via scanning electron microscopy (SEM) and X-ray diffraction (XRD) testing. The objective is to facilitate a beneficial synergetic interaction among these materials to develop highly permeable, crack-resistant concrete. Key findings of this study are: (1) The study unveils the impact of the concentration of three additive materials on the concrete's compressive strength, tensile strength, and penetration height, thereby outlining their significant influence on the mechanical properties and impermeability of the concrete; (2) An integrated scoring method determined the optimal composite dosage of three materials: 15% fly ash, 2% CCCW, and polypropylene fibers at 1.5 kg/m3. This combination increased the concrete's compressive strength by 12.5%, tensile strength by 48.4%, and decreased the average permeability height by 63.6%; (3) The collective introduction of these three materials notably augments the hydration reaction of the cement, resulting in denser concrete microstructure, enhanced bonding between fibers and matrix, and improved concrete strength and durability.

Experimental studies of the influence of biaxial bending on the crack resistance of reactor pressure vessel steel

Background: to assess the residual life of nuclear reactor hulls in Ukraine, normative temperature dependences of the crack resistance of hull steels obtained on standard samples with a deep through crack under plane strain conditions are used. However, it is known that the thickness of the wall of the reactor body is subject to biaxial loading, which affects the value of the crack resistance characteristics. Therefore, in order to substantiate the possibility of lengthening beyond the design resource of VVER-1000 reactor hulls, an experimental study of the effect of biaxial load on the crack resistance characteristics of hull reactor steel 15X2NMFAA is relevant. Objective: development of an experimental technique and investigation of crack resistance under biaxial loading on small-sized samples in the the brittle-ductile transition temperature range of reactor steels. Methods: on the basis of numerical and engineering calculations, a specimen was developed, the corresponding additional equipment for its tests under biaxial loading on a uniaxial servo-hydraulic machine. The influence of biaxial bending on the fracture toughness of reactor steel 15X2NMFAA was experimentally investigated. Results: the results obtained on cruciform specimen are calculated according to the ASTM 1921 standard and plotted on the Master curve (temperature dependence of fracture toughness). The analysis showed that the data on crack resistance obtained on samples with "short" (a/W=0.1...0.2) linear and surface semi-elliptical cracks exceed the upper limit of the confidence interval of the Master curve, and biaxial loading of cruciform specimen reduces crack resistance compared to uniaxial loading.

ТРІЩИНОСТІЙКІСТЬ БЕТОНІВ З ПОЗИЦІЇ МЕХАНІКИ РУЙНУВАННЯ (ОГЛЯД)

This paper presents the generalized results of the analysisand synthesis of scientific and technical sources of investigation the heavy concrete on the basis of fracture mechanics for the last 25-30 years.New criteria and models for heavy concrete, which were obtained during this period have been described and generalized, in particular, a new deformation model of concrete crack resistance on the basis of fracture mechanics. The analysis of results of experimental and theoretical researches of heavy concrete crack resistance on disk-shaped samples at eccentric stretching by concentrated forces has been presented. A number of methods have been elaborated i.e. a method for experimental determination of the concrete crack resistance characteristics under static loads, a method for determining the length of the fracture zone in the crack, the relationship between the mechanical characteristics of heavy concrete and the parameters of acoustic emission measurement. The method of concrete cracking resistance with the addition of basalt fiber was also developed and the influence of basalt fiber on crack resistance and crack opening was studied in field tests. The generalized results have been presented.It has been stated about the significant development over the last three decades of methods for determining the strength, crack resistance and deformation of concrete in reinforced concrete elements from the standpoint of reinforced concrete mechanics and mechanics of concrete destruction. The conclusions about the expediency of using the Leonov-Panasyuk deformation model for concrete and the prospects for fictitious crack model have been made.On the basis of the generalized data given in the specified publications the technique of technical diagnostics and a technique of repair and restoration works at strengtheningwith use of modern technologies and materials has been developed that gives the chance to increase considerably a resource and reliability of reinforced concrete buildings and constructions

CRACK RESISTANCE CHARACTERISTICS OF MICROSTRUCTURE OF HAVERSIAN CORTICAL BONE

Background: The current research on crack propagation resistance characteristics of osteons is based on the single osteon model, which cannot reflect the interaction among osteons and the influence of material-property changes on the crack propagation. Moreover, the Haversian canal and the cement line were not included in the model, which could not reflect the influence of the true structural characteristics of the cortical bone on the microcracks. Objective: To investigate the effects of osteons, cement line and its material parameters on the stress intensity factor at the crack-tip based on theoretical formula calculation and finite element calculation. Results: The single osteon model, multi-osteon model and Haversian cortical bone model were established according to the microstructural characteristics of Haversian cortical bone. The calculation results of the first two models show that the “soft” osteon accelerates the crack propagation and the “hard” osteon hinders crack propagation, and the effect of multi-osteon model on a microcrack is significantly larger than that of single bone model. The calculation results of Haversian cortical bone model show that the stress intensity factors at both ends of the microcrack decreased when the distance from the “soft” osteon was within a certain range ([Formula: see text]). The stress intensity factor of endpoint ‘a’ in the crack-tip increases sharply when the microcrack is close to the osteon. Conclusions: The analysis results of the three models present that the microcrack propagation is affected by the material properties as well as the quantity of osteon, and the cement line is conductive to enhance the fracture toughness of the cortical bone.

APPLICABILITY ASSESSMENT OF THE VICKERS INDENTATION FOR DETERMINING THE FRACTURE TOUGHNESS OF YTTRIA-STABILIZED ZIRCONIA

Crack growth resistance of ZrO2-(3-8) mol% Y2O3 ceramics was investigated. Young's modulus by the ultrasonic flaw detection method were determined. Vickers hardness and parameters of cracks after Vickers indentation were obtained. Based on the Young's modulus values, Vickers hardness, and parameters of cracks, the fracture toughness of the investigated ceramics was calculated using 9 different equations of the Vickers indentation method. A comparative analysis of the calculated fracture toughness values with those obtained by the single-edge notch beam method was carried out. It was found that choosing the optimal equation for calculating fracture toughness by the Vickers indentation method is quite difficult and requires comparison with the results of standardized tests. It was shown that to determine crack resistance characteristics of the yttria-stabilized zirconia ceramics, the use of only the Vickers indentation method without comparison with other methods of fracture mechanics is incorrect.

Evaluation of dispersion reinforcement in concrete in terms of strength and crack resistance

Introduction. The purpose of the study was to evaluate the effectiveness of dispersed concrete reinforcement in terms of strength and crack resistance.Materials and methods. When conducting research, test methods were used, regulated by the provisions of national standards, equipment specially designed for this study was used.Results. The results of testing fiber-reinforced concretes made using low-modulus and high-modulus fibers are presented.Discussion and conclusions. As a result of the analysis of the data presented, it is shown that in order to assess the effectiveness and the correct choice of reinforcing fibers, it is not enough to characterise fiber-reinforced concrete only by tensile strength in bending. For a more accurate assessment, it is proposed to use crack resistance characteristics, for example, the critical stress intensity factor, or to supplement the description of the advantages of dispersed reinforcement with the features of the behavior of fiber-reinforced concrete under load.

Structural Response of High-Strength Wire-Reinforced UHPC Slabs Subjected to Bending.

Using high strength wire (HSW) as a longitudinal reinforcement in UHPC can make full use of the outstanding properties of UHPC. In this paper, the flexural test was carried out on normal rebar-reinforced UHPC (NRRU) and HSW reinforced UHPC (HSWRU) slabs. The cracking resistance, failure modes, bearing capacity and deformation characteristics of specimens were investigated. The test results indicated that both HSWRU and NRRU specimens exhibited excellent flexural performance under concentrated loads. Fewer inclined cracks and a slower cracking development process were observed for HSWRU specimens, and brittle failure did not occur during the whole loading process. As compared to HSWRU specimens, the cracking and ultimate load of NRRU specimens increased by 24.64% and 85.47%, respectively, due to a higher reinforcement ratio. Then the theoretical method available for flexural capacity and ductility calculation was proposed, and the feasibility was substantiated through test results. In addition, the traditional deformation ductility coefficient was found to be 30% conservative against the applied energy ductility coefficient. Finally, the extensive parametric analysis revealed that the increase of the reinforcement ratio and the strength of the steel rebar significantly enhanced the ultimate capacity, while the ductility coefficient was obviously weakened. Inversely, those two factors had little impact on the cracking capacity. Moreover, section height was found to be beneficial for both the flexural capacity and ductility of specimens.

Effects of Fly Ash Dosage on Shrinkage, Crack Resistance and Fractal Characteristics of Face Slab Concrete

The crack resistance of face slab concretes to various shrinkages is crucial for the structural integrity and the normal operation of concrete-faced rockfill dams (CFRDs). In this work, the effects of fly ash with four dosages (i.e., 10%, 20%, 30% and 40%) on the drying shrinkage, autogenous shrinkage and the cracking resistance of face slab concrete were studied. Besides, the difference in shrinkage behavior due to fly ash addition was revealed from the viewpoint of the pore structure and fractal dimension of the pore surface (Ds). The findings demonstrate that (1) the incorporation of 10–40% fly ash could slightly reduce the drying shrinkage by about 2.2–13.5% before 14 days of hydration, and it could reduce the drying shrinkage at 180 days by about 5.1–23.2%. By contrast, the fly ash addition could markedly reduce the autogenous shrinkage at early, middle and long-term ages. (2) Increasing fly ash dosage from 0 to 40% considerably improves the crack resistance of concrete to plastic shrinkage. Nevertheless, the increase in fly ash dosage increases the drying-induced cracking risk under restrained conditions. (3) The pore structures of face slab concrete at 3 and 28 days become coarser with the increase in fly ash dosage up to 40%. At 180 days, the pore structures become more refined as the fly ash dosage increases to 30%; however, this refinement effect is not as appreciable as the fly ash dosage increases from 30% to 40%. (4) The Ds of face slab concrete is closely related with the concrete pore structures. The Ds of face slab concrete at a. late age increases from 2.902 to 2.946 with increasing of the fly ash dosage. The pore structure and Ds are closely correlated with the shrinkage of face slab concrete. (5) The fly ash dosage around 30% is optimal for face slab concretes in terms of lowering shrinkage and refining the pore structures, without compromising much mechanical property. However, the face slab concretes with a large fly ash dosage should be well cured under restrained and evaporation conditions at an initial hydration age.

DETERMINATION OF CRACK RESISTANCE OF CONCRETE ON THE BASIS OF DESTRUCTION MECHANICS

Purpose The objective of the paper is to study and generalize the characteristics of heavy concretes crack resistance based on real experimental research, – the coefficient of stress intensity Kсexp, the coefficient of energy characteristic of effective surface energy γexp, opening the banks at the top of the crack δсexp and establishing the dependence of acoustic emission AE-SEq with the specified parameters of concrete crack resistance and in accordance with current standards. Methodology. To achieve this goal, a review and synthesis of scientific and technical sources were made and comprehensive experimental and analytical studies were conducted Kсexp, γexp ,δсexp and the dependences of acoustic emission are established AE–SEq with the specified parameters of crack resistance of concrete and in accordance with current standards. A series of experiments was made to study the concrete crack resistance, in particular, to determine the stress intensity coefficient (SIC). In parallel, the relationship with the measurement parameters of AE acoustic emission in heavy concretes of five series of different composition and strength was studied. Longitudinal and transverse deformations were measured with indicators, which made it possible to determine the Poisson’s coefficient V. Under load, fracture diagrams were recorded on a two – coordinate recorder in the coordinates "Force P-opening of the crack v on the line of force action". Results. The analysis of scientific and technical sources of domestic and foreign materials for determining the heavy concretes crack resistance is carried out. The characteristics of crack resistance of concrete various compositions and strength, in particular the coefficient of stress intensity, are obtained Kсexp of the coefficient of energy characteristic of effective surface energy γexp, opening the banks at the top of the crack δсexp and the corresponding dependencies are installed AE–SEq with the specified parameters of concrete crack resistance. The stress intensity coefficient is determined with the parameters α0, β0 when loading with concentrated forces at certain points of applying the load. The influence function of geometric parameters of the sample is also determined f(α0, β0,ε), which was determined by calibration curves. A diagram of calculating the energy balance and a graph of load changes from the intensity AE are obtained. Based on the P-v diagrams, a formula is obtained for determining δсtheor at the top of the crack and graphical dependency δс from change fctk. The experimentally known ratio of fracture mechanics is tested δсσ0=2γ. Scientific novelty. This paper summarizes a number of experimental and theoretical researching the heavy concrete crack resistance features based on fracture mechanics. In particular, the following was specified and established: stress intensity factor Kсexp surface energy coefficient ; opening the banks at the crack tip ; the dependences between АЕ–SEq with the specified parameters of concrete crack resistance are established; the classical relation of fracture mechanics for concretes is confirmed. In addition, based on the fracture mechanics approaches for five series of concrete disk samples the force energy γ and deformation crack resistance features are determined by independent experimental methods. Practical significance. The comparison of the specified approaches of fracture mechanics is carried out and satisfactory convergence of the received results for heavy concretes is established.

Thermal, chemical and rheological properties of asphalt binders extracted from field cores

The intermediate-temperature performance of extracted asphalt binders (EABs) is altered when recycled asphalt shingles (RAS) and/or reclaimed asphalt pavement (RAP) are included in asphalt mixes. This happened as a result of the RAP’s aged asphalt binder and the RAS’s oxidized air-blown asphalt. Thus, the rheological properties of EABs from field cores were examined at intermediate temperatures. The fatigue life and the Superpave fatigue cracking parameter were among the rheological properties. Thermogravimetric analysis and Fourier transform infrared were used to analyze EABs’ thermal and chemical characteristics, respectively. The relationships between EABs’ fatigue cracking resistance, thermal, and chemical characteristics were scrutinized. Ages of mixes, percentages of RAP and/or RAS, and intermediate performance grade (PG) temperatures of virgin asphalt binders (VABs) controlled the resistance of EABs to fatigue cracking. Considering VABs with the same intermediate PG temperatures, EABs from older mixes with higher RAS percentages had higher resistance to fatigue cracking than those from younger mixes with lower RAP percentages. When RAP percentages in asphalt mixes were increased, EABs’ resistance to fatigue cracking deteriorated. Thermal and chemical analyses along with rheological characteristics are suggested as indicators of EABs’ intermediate-temperature performance.

Calculation and Experimental Method of Evaluation of Residual Working Resource of Reinforced Rods of Concrete Structures of Hydrotechnicalreinforced Structures

The work carried out complex and systematic studies based on of which the causes of accidental destruction of reinforcement of reinforced concrete structures of hydraulic structures is established, which is that corrosion damage to metal reinforcement is accompanied by its active flooding and embrittlement, resulting in reduced material properties against corrosion and mechanical destruction of reinforced concrete structures, especially after 20-40 years of operation. Based on existing approaches to the assessment of ageing equipment, developed in various branches of mechanical engineering, including the construction industry, identified trends and shortcomings in determining the efficiency of metal structures and their residual life, in connection with which the calculation and experimental methods of using the criteria of crack resistance, sensitive to changes in the structure of the metal during long-term operation. It is established that the decrease in crack resistance characteristics in the surface layers of reinforcement of reinforced concrete structures in contact with the aggressive environment is caused by the degrading effect of hydrogen on the crystal structure of the metal. The calculated-experimental method is offered, allowing to carry out engineering forecast estimation of residual (working) resource of the reinforced concrete designs operated in corrosive-aggressive environments of hydraulic engineering constructions, which adequately reflects physical and mechanical processes in metal which occur during its long operation.

On Experimental Procedure Development for Evaluating the Effect of Biaxial Loading on the Static Crack Resistance Characteristics of Reactor Vessel Steels

On Experimental Procedure Development for Evaluating the Effect of Biaxial Loading on the Static Crack Resistance Characteristics of Reactor Vessel Steels

ВЛИЯНИЕ КРУПНОГО ЗАПОЛНИТЕЛЯ НА ЭНЕРГЕТИЧЕСКИЕ И СИЛОВЫЕ ХАРАКТЕРИСТИКИ СТАЛЕФИБРОБЕТОНА

At present, composite materials are gaining more and more development in construction, including the use of dispersed reinforced concrete, which is due to its significantly improved physical, mechanical and operational characteristics compared to traditional concrete and reinforced concrete. The article presents the results of the influence of coarse filler in the composition of the composite on the energy and power characteristics of the crack resistance of fiber-reinforced concrete reinforced with steel anchor fibers. The process of deformation and the mechanism of destruction of steel fiber reinforced concrete have been studied. To do this, in accordance with the provisions of GOST 29167 "Methods for determining the characteristics of crack resistance (fracture toughness) under static loading", steel-fiber-reinforced concrete sample beams were tested with control of the applied load and the deflection caused by it. Based on the data obtained, diagrams of the dependence of the load on the deflection were constructed, after their processing and additional constructions, the energy costs for static destruction, tensile strength in bending, and the stress intensity factor were determined. It has been established that the value of the conditional specific effective energy consumption for static failure and tensile strength in bending of fiber-reinforced concrete samples with a matrix of heavy concrete with coarse aggregate turned out to be lower than that of fiber-reinforced concrete samples with a matrix of fine-grained concrete, which is explained by the lower adhesion of the steel anchor fiber to the matrix, and a corresponding decrease in their efficiency.