Strength Characteristics of Quartzoid Glasses Doped with Cesium

Revisiting the concept of characteristic compressive strength of concrete

This paper reviews findings of research on the dependence fiber concrete with steel, polypropylene and glass fiber for fine-grained concrete, as fiber concrete with improved strength and deformation characteristics is increasingly used in construction. At the same time, fibers of different composition and origin, geometric characteristics and physical and mechanical properties are used as dispersed reinforcement. The characteristics of the fiber types that can be used to manufacture fiber concrete are given. The article presents the main characteristics of the considered fiber types. The authors studied the effect of different fiber types on the strength characteristics in the fine-grained mix concrete. The article’s authors determined as a whole that the addition of steel fibers reduces concrete shrinkage and significantly raises the concrete’s strength characteristics compared to polypropylene fibers. The experimental results studies in the studied articles indicated the productivity using fibers as comparison with fine-grained concrete without fiber. The article compares the main types of fiber concrete, and notes the high strength indicators of this actively developing material. The specialists can also be interested in the fact that each type of fiber gives certain properties to concrete with its advantages and disadvantages.KeywordsFibersFine-grained concreteShort AR-glass fibersStrength

To reveal the influence of water content on the strength characteristics and brittle-plastic failure process of Xiashu loess, the direct shear test and unconfined compressive strength test of Xiashu loess with different water content were carried out, and the influence of water content on its strength characteristics and brittle-plastic failure transformation characteristics was studied. Eight kinds of Xiashu loess with different moisture contents were designed, and a direct shear test and uniaxial compression test were carried out, respectively. The results show that with the increase in water content, the shear strength and unconfined compressive strength of Xiashu loess decrease continuously. The influence of water content on cohesion in the shear strength index is greater than that of the internal friction angle. The relationship curve between cohesion and internal friction angle and water content shows obvious segmentation. When approaching the optimal water content, the downward trend is slowed down. When the water content is constant, the shear strength of the sample will also increase with the increase of normal stress. When the water content is 12% to 15%, the failure mode of Xiashu loess is a brittle failure, and the unconfined compressive strength decreases by 43.23%. When the water content is 15% to 16%, the failure mode of Xiashu loess is a transitional failure, and the unconfined compressive strength decreases by 60.38%. When the water content is greater than 16%, Xiashu loess shows plastic failure, and the unconfined compressive strength decreases slightly.

All concrete mechanical properties given in design codes of concrete and reinforced concrete structures are correlated with the characteristic compressive strength fck. According to the EN 206-1 code, the characteristic strength is defined as the strength value below which 5 % of the population of all possible strength test results for given volume of concrete can be found. The value of fck can be defined as 5 % quantile of the statistical distribution of the concrete compressive strength, tested on cylindrical samples with a diameter of 150 mm and a height of 300 mm or on cubic samples with dimensions 150 × 150 × 150 mm assuming the conversion factor of 0.8. In order to verify compliance of strength of the considered concrete with the designed characteristic strength (ascribed to concrete class), it should be checked if the test results meet the appropriate statistical criteria. The characteristic strength defined by specifying of concrete class is determined at the designing stage of the structure and it is the basic controlled parameter, providing the requirements are fulfilled by the producer. Despite numerous publications on disadvantages of the code compliance criteria, marginalization of the problem is still visible. Concepts and methods based on probabilistic or statistical approaches are often sourced of skeptical views on quality control because they are not very familiar to most engineers. In the paper the assessment of the code compliance criteria has been made using the numerical simulation on the basis of the programs which has been written in C++. The innovative method for estimation test coefficients values contained in the code compliance criteria has been proposed. This method was developed on the basis of fuzzy methods.

1. The experimental investigations conducted indicate a significant influence of misalignment of application of the load on the measurement results of the characteristics of short-term strength and plasticity of a brittle cermet, tungsten-copper pseudoalloy, in the 20–1000°C temperature range. 2. A linear relationship of the results of measurements of the tensile strength of tungsten-copper pseudoalloys to the level of misalignment of application of the load was established. 3. The error in the results of measurements of the mechanical characteristics of the tungsten-copper pseudoalloy tested under misalignment conditions increases with a decrease in plasticity of the material. The characteristics of plasticity of the material. The characteristics of plasticity are more sensitive to misalignment than the characteristics of strength. 4. The effectiveness of use of clamps with boron nitride powder fillers in high-temperature tests (up to 1000°C) of brittle materials under conditions of misalignment of application of the load was shown. A difference was noted in the reasons for the occurrence of misalignment in the use of clamps for speciments with cylindrical heads and of those with powder fillers. The use of the latter reduces misalignment by four to five times.

Welded joint generally has heterogeneity of strength, material, and fracture toughness. It is important to understand the characteristics of material strength and fracture of welded joint considering heterogeneous effect. Furthermore, material behavior becomes more complicated when the welded joint is subjected to dynamic loading like as earthquake. In this paper, characteristics of strength and fracture of an undermatched joint under dynamic loading is studied by round-bar tension tests and thermal elastic-plastic analyses. The results show that the strength and fracture of the undermatched joints should be evaluated based on the effects of the strain rate and the temperature including temperature rise during the dynamic loading. Tensile strength and yield stress of the undermatched joints increase with strain rate and with decreasing temperature. The strength of the soft layer approaches to that of the base metal when the thickness of the soft layer becomes smaller, and does not depend on strain rate. Finally, it is found that the stress-strain distribution affects the fracture characteristics like such as ductile-to-brittle transition behavior. The fracture characteristics are well precisely explained from the results obtained by numerical analysis.

1. In the uniaxial static elongation of geometrically similar samples, the strength characteristics (σB and σ0.2) and the relative elongation (e) are practically independent of sample diameter. The relative contraction (ψ) increasing with falling diameter, this effect being particularly sharp below 4 mm. 2. In estimating the mechanical properties of materials tested in two states (annealed and coldworked), the diameter has the greater effect on the relative contraction for the cold-worked metal, i. e., the scale effect appears more strongly for a less well-developed process of plastic deformation, such as occurs in high-strength samples. 3. In the shock (impact) extension of geometrically similar samples by loads of equal mass, over the range of small elastic-plastic deformations the relative elongations are no longer constant when the specific absorbed impact energy remains so (A/V=const); however, in the case of a well-developed process of plastic deformation the general law of similarity remains intact. 4. An estimate of the ductility of high-strength materials based on the relative contraction of samples of small diameter (under 4 mm) tends to be too high (by 20 to 40%) and cannot serve as a criterion for justifying any particular technical operation carried out with a view to improving the mechanical properties of metals.

In this paper, the influence of the size of coarse aggregate and aggregate/cement ratio on the strength and abrasion properties of pervious concrete is reported. Pervious concrete mixes are prepared with single-sized aggregates (4.75, 10 and 12.5 mm), blends consisting of three different aggregate sizes and aggregate-to-cement ratios of 3.2, 4.5 and 5. Experimental results indicate that the strength characteristics and abrasion resistance of pervious concrete decrease with increase in the size of aggregate as well as aggregate-to-cement ratio. As voids created by higher size aggregates were filled up by lower size aggregates, mixtures with blended aggregates achieved the lowest void content. Existing equations relating splitting-tensile and flexural strengths with cube compressive strength is verified. As density increases, void content of pervious concrete mixtures decreases. A simple regression model relating abrasion resistance index, which is defined as the ratio of square root of dimensionless number of revolutions to weight loss/initial weight of specimen in Cantabro test, to cube compressive strength of concrete is proposed. The developed model had reasonable goodness of fit, which indicated high accuracy.

Geogrid reinforcement has a limiting effect on the lateral deformation and thus improves the shear strength of the soil, the overall strength of the soil and the overall stability of the corresponding geotechnical structure. In this study, large-scale triaxial tests without and with geogrid reinforcement were conducted on three typical gravelly soils in Xinjiang using a large-scale triaxial apparatus. The shear strength and deformation characteristics of gravelly soils with different particle shapes and the stress-strain relations, strength characteristics, damage patterns, and reinforcement effects of gravelly soils with and without reinforcement were investigated. Geogrid reinforcement effectively enhances the strength of the soil; the internal friction angle remained relatively constant with and without reinforcement, whereas the cohesive force increased significantly. The reinforcement effects interpreted from the results obtained from the triaxial tests were discovered when a certain deformation or relative displacement with the reinforcement materials of the soil occurred. Under uniform test conditions, the volumetric strain of the samples of gravelly soil with reinforcement significantly decreased with increasing confining pressure, and the difference in volumetric strains with and without reinforcement was greater when the confining pressure was higher. The highlight of this study is its significance in explaining the reinforcement mechanism in gravelly soils and in selecting engineering design parameters.

One of the ways to improve the strength and deformation characteristics of reinforced concrete structures is the use of indirect reinforcement. Such reinforcement, located perpendicular to the compressive force, by limiting transverse deformations creates a volumetric stress state and increases the efficiency of concrete in compression. The article presents a method for assessing the stress-strain state of structures, which allows to take into account the reserves of bearing capacity and apply more economical design solutions. The calculation of strength is considered and the diagram of concrete deformation reinforced by indirect reinforcement is obtained. It is shown that the relative deformations at the apex of the compression diagram depend mainly on the relative level of lateral reduction and concrete strength. It is shown that the lower the concrete class, the less indirect reinforcement affects its strength characteristics, but the limiting deformations increase more strongly, and therefore an almost horizontal section appears near the top of the diagram, the longer the concrete class and the higher the reinforcement percentage.

Annotation. Statement of the problem. Heat treatment significantly enhances the properties of metals and alloys, thereby extending their service life. The microstructure of many metallic materials undergoes transformation following heat treatment. The operation of oil and gas fields containing hydrogen sulfide (H₂S) necessitates the use of tubing and casing pipes resistant to sulfide stress cracking. Currently, imported pipes, such as those of grade C75-2, are employed for this purpose. Heat treatment of steels improves the operational properties of pipeline steels used in aggressive H₂S-containing environments. Consequently, testing manganese steel under the MCKP 01-85 methodology, which involves assessing resistance to sulfide stress cracking through constant strain rate testing in an H₂S-containing aggressive environment, is particularly relevant. The H₂S environment induces hydrogen embrittlement and stress corrosion cracking, leading to the formation of cracks with self-similar (fractal) morphology. To study this morphology, various approaches are employed alongside fractal theory. This study focuses on investigating the effects of an aggressive hydrogen sulfide (H₂S) environment on the microstructure and properties of manganese steel 30G2. Purpose and setting of the task. The aim of this study is to evaluate the impact of an aggressive H₂S environment on the strength and ductility characteristics of manganese steel, as well as to analyze changes in the fracture mechanisms to develop recommendations for enhancing its operational reliability. To achieve this objective, the following tasks must be accomplished: 1. Conduct heat treatment of manganese steel and perform microstructural analysis before and after exposure to the H₂S environment. 2. Perform fractographic analysis of the fracture surfaces of the steel. 3. Investigate the effect of hydrogen embrittlement induced by the H₂S environment on the microstructure and properties of manganese steel. Materials and Research Methods. Experimental tests were conducted on samples of 30G2 manganese steel in two states: the initial state (after heat treatment) and after prolonged exposure to an H₂S environment (720 hours, according to the MCKP 01-85 methodology). In the initial state, the steel exhibited high mechanical properties: ultimate tensile strength (σВ) of 842 MPa, yield strength (σT) of 736 MPa, relative elongation (δ5) of 19.6%, and relative reduction in area (ψ) of 65.6%. These values significantly exceed the standard specifications for 30G2 steel, indicating the effectiveness of the applied heat treatment. Research material and methods. Following exposure to the H₂S environment, a slight reduction in strength characteristics (by 2–3%) was observed, indicating the steel's resistance to strength degradation under aggressive conditions. However, ductility experienced a more significant decline, with relative elongation and reduction in area decreasing by 10–13%. Despite this, the ductility values remained within acceptable limits to ensure reliable operation of coupling pipes. After exposure to the H₂S environment, a transition to a more brittle fracture behavior was noted, accompanied by the formation of hydrogen-induced cracks. These changes are attributed to hydrogen penetration into the steel’s microstructure, which causes localized embrittlement and reduced ductility. The obtained results confirm the suitability of the modified 30G2 steel for use in coupling pipes for oil and gas pipelines operating in aggressive H₂S environments. However, the observed changes in ductility and fracture behavior highlight the need for further optimization of the steel’s chemical composition and heat treatment regimes. Specifically, it is recommended to consider the addition of alloying elements to enhance resistance to hydrogen embrittlement and to improve heat treatment technologies to minimize internal stresses and microstructural defects. These measures will contribute to enhancing the durability and reliability of pipes under challenging operational conditions. Conclusions. 1. The mechanical properties of coupling pipes made from 30G2 manganese steel in the initial state are characterized by high strength (σВ ≈ 842 MPa, σТ ≈ 736 MPa) and good ductility (δ₅ ≈ 19.6%, ψ ≈ 65.6%). These values exceed the standard specifications for 30G2 steel, indicating effective heat strengthening of the material. 2. After exposure of the samples to a hydrogen sulfide (H₂S)-saturated environment for 720 hours, the reduction in strength is minimal, at only 2–3%, demonstrating the resistance of 30G2 steel to strength degradation under H₂S conditions. 3. The most significant changes are observed in the ductility properties: relative elongation and reduction in area decrease by 10–13%, which is associated with hydrogen embrittlement and the formation of intergranular cracks. However, even after H₂S exposure, the ductility remains satisfactory for operational purposes (δ₅ > 14%, ψ > 54%). 4. Fractographic analysis revealed a transition from ductile-brittle fracture in the initial state to a more brittle fracture after H₂S exposure, confirming the accumulation of hydrogen in the steel’s microstructure and its influence on crack formation. 5. Overall, the modified 30G2 steel exhibits satisfactory resistance to H₂S-induced effects and can be considered a promising material for oil and gas pipelines operating in aggressive H₂S environments. To enhance durability, further optimization of the chemical composition and heat treatment regimes is recommended (e.g., alloying with Cr/Mo, additional tempering at 600–650 °C).

Deformational and breakage behaviors of concrete and cement mortar greatly influence various engineering structures, such as dams, river bridges, ports, tunnels, and offshore rig platforms. The mechanical and petrophysical properties are very sensitive to water content and are controlled by the liquid part in pore spaces to a large extent. The objective of this paper is to investigate the water saturation effect on the strength characteristics and deformability of cement mortar under two loading conditions, static and dynamic compression. A set of cement mortar samples was prepared and tested to study the mechanical behavior in dry and saturated states. The first part of the research incorporates the study of static mechanical properties for dry and brine-saturated cement mortar through uniaxial compressive strength tests (UCS). Second, drop-weight impact experiments were carried out to study the dynamic mechanical properties (impact resistance, deformation pattern, and fracture geometry) for dry and saturated cases. The comparative analysis revealed that water saturation caused substantial changes in compressive strength and other mechanical characteristics. Under static loading, water saturation caused a reduction in strength of 36%, and cement mortar tended to behave in a more ductile manner as compared to dry samples. On the contrary, under dynamic loading conditions, water saturation resulted in higher impact resistance and fracture toughness as compared to dry conditions. In addition, fractures could propagate to smaller depths as compared to dry case. The study will help resolve many civil, mining, and petroleum engineering problems where cement structures undergo static as well as dynamic compression, especially in a hydraulic environment where these structures interact with the water frequently. To the best of our knowledge, the effect of water saturation on the dynamic mechanical properties of cement mortar has not been well understood and reported in the literature.

Reinforced wooden beam structures under the influence of critical loads are subject to brittle fracture, which is dangerous when operating beams in buildings. To solve this problem, reinforcement of wooden beams for civil and industrial buildings was invented using steel rope as a reinforcing element. The rope is located in the stretched area of the beams along the original S-shaped trajectory. Numerical studies of the deformation of the reinforcement model using the LIRA program are performed. Based on numerical studies, samples were made for testing for pulling S-shaped anchoring elements from solid wood. The analysis of deformation - strength characteristics based on the results of tests on a tensile testing machine glued curved rods. A triple increase in the ductility of the deformation of the paste in the zone of destructive loads was revealed. The main problems of this type of reinforcement are the appearance of stress concentrators in areas with a small radius of curvature of the reinforcement. As a result of the study, the optimal trajectory of the reinforcement insert was determined with the aim of obtaining higher strength and deformation characteristics - with a reduced oscillation amplitude. The possibility of using structures in the form of safety elements has been established, which allows to increase the destruction time of beam systems when exceeding the permissible load.

Natural rock mass contains defects of different shapes, usually filled with inclusions such as clay or gravel. The presence of inclusions affects the failure characteristics and mechanical properties of rock mass. In this study, the strength and failure characteristics of rock with inclusions were studied using the particle flow code under uniaxial compression. The results show that the presence of inclusions not only improves the mechanical properties of rock with defects but also increases the bearing capacity of rock. Circular inclusion has the most obvious effect on improving model strength. The inclusions affect the stress distribution, development of initial crack, change in crack propagation characteristics, and failure mode of rock. In defect models, concentration area of the maximum tensile stress is generated at the top and bottom of defect, and the maximum compressive stress is distributed on the left and right sides of defect. In filled models, the tensile stress and compressive stress are uniformly distributed. Failing mode of defect models is mainly tensile failure, while that of filled models is mainly shear failure.

A study on workability, strength and microstructure characteristics of graphene oxide and fly ash based concrete