Destructive Load Research Articles

A geometrical morphology-enhanced computer vision approach for structural health assessment

Images contain abundant valuable information about the health state of the photographed infrastructures. However, local defects are mostly detected in vision-based structural health monitoring (SHM), while global safety and risk at a larger scale are rarely assessed. To fill up this gap, a geometrical morphology-based image analysis framework is developed for structural global health assessment. A structured random forest edge detector is adopted to extract the edges in an image, and the morphological operations are subsequently used to highlight the edge skeleton, from which the continuous line segments are estimated by the Hough transform. Via these operations, the intrinsic geometrical features of different structures can be extracted and highlighted in an unsupervised manner and at a real-time speed. A global health indicator, line-to-edge ratio, is finally calculated to assess the structural state according to the fact that the deterioration of material will introduce abundant irregular edges in an image and break the lines at the structure boundaries. A destructive beam loading test video and a set of images from different bridge piers are analyzed for verification. The images are taken from arbitrary, uncontrolled, and backlighting views. The results show that the proposed framework can correctly quantify the health condition and detect the occurrence of damage for the in-field infrastructures.

Increasing the durability of soldering wearresistant steel by regulating the redistribution of thermal stresses

Abstract. Problem. The tangential load has a significant influence on the stress state during pressure treatment of metals in the contact zone and on the nature of fatigue failure. As a result of plastic deformations, stresses are redistributed in places of concentration of defects. Since the amount of plastic displacements depends on the level of tangential stresses, the critical number of internal breaks in the material should increase with the increase in the intensity of stresses σ, as the quantity responsible for the formation of the material. Goal. The purpose of the work is to determine the critical values of external loads and the angle of initial propagation of cracks (crack-type defects) at which local or complete destruction of the body will occur. Methodology. Brazing with wear-resistant alloys of the Cr-MnTi-Si and Cr-Mn-Mo-Ti-Si systems was carried out on samples made of 50HNM steel according to the "slide" scheme with flux-cored wire. The effect of temperature on the strength and wear resistance of alloys was studied at elevated temperatures under the conditions of a volumetric stress state using the calculated criterion equations of fracture mechanics. Calculations were made using Mathcad software.Originality. It is theoretically substantiated that at temperatures of 673...873 K and large ratios of crack radii to their depth, mechanical and thermal stresses are responsible for the destruction of the investigated wear-resistant alloys, with an increase in temperature and a decrease in the ratio of the crack radius to its depth, a factor that affects their destruction, there is accumulated plastic deformation. Practical value. Analysis of the results of the influence of temperature stresses on the ultimate external load shows: – at T=673 K, the temperature stresses are 33% of the destructive load;– at T=793 K, the temperature stresses are 44% of the destructive load; – at T=893 K, temperature stresses are 50% of the destructive load

ЧИСЛЕННЫЙ ЭКСПЕРИМЕНТ В ПК ANSYS ДЛЯ ФЕРМЫ, СОЗДАННОЙ ПРИ ПОМОЩИ АДДИТИВНЫХ ТЕХНОЛОГИЙ, НА РАЗРУШАЮЩУЮ НАГРУЗКУ

The article explores the possibility of using the Ansys software package to model slabs designed as beams manufactured using a 3D printer. To evaluate the effectiveness of this model, a numerical experiment was conducted, during which the beam structure was subjected to a destructive load. The simulation results were compared with the results of a physical experiment to verify the accuracy of the model. The input data for the calculation were based on parameters similar to those of an experiment conducted by Diego Veloso at the University of São Paulo, where a truss beam was studied. The model was built using both solid and beam elements, with loads applied to the nodes of the model as distributed forces over the area, replicating the conditions of the full-scale experiment. The calculation results revealed that the failure of the beam begins when the load on the nodes reaches 500 kg. In a full-scale experiment, the destruction occurred when a load of 700 kg was reached.These data coincide with the results of the full-scale experiment, confirming the accuracy of the chosen modeling method. Thus, the proposed calculation method can be successfully applied to the design of load-bearing elements of buildings constructed using layer-by-layer 3D printing with construction printers.

Tension Performance Prediction and Experiment of Optical Smart Composites Using Micromechanical Failure Theory

Abstract Embedding fiber optic sensors in composites can long-term instantly monitor the deformation and damage within the composite structure, which realizes structural health monitoring and life prediction. However, fiber embedding generally brings damage in terms of the composite material integrity and continuity, resulting the extreme stress concentration in the interface of the optical fiber and composite. Therefore, the mechanical properties of the composite material are potentially influenced unfavorably. To investigate the influence of microstructures such as optical fibers on the macroscopic tensile mechanical properties of composites, this paper develops a progressive damage analysis model inspired by the micromechanical failure theory. The established model can predict the stiffness and strength properties of fiber smart composites. The model is further verified by comparing the obtained tensile failure mechanism with the experimental results. The results show that the maximum relative error of the destructive load is only 3%, which demonstrates the accuracy and validity of the model. The work of this paper can provide guides for the optimization and strength prediction of smart composite structures with embedded optical fibers.

ПЛАНИРОВАНИЕ ЭКСПЕРИМЕНТА ПРИ ИССЛЕДОВАНИИ СИЛОВОГО ВЗАИМОДЕЙСТВИЯ ФУНДАМЕНТОВ С ГРУНТОВЫМ ОСНОВАНИЕМ

The article presents the results of studies of foundation models when breaking along inclined sections and in the form of punching. For rational planning of experiments, a large combination square was constructed, consisting of 25 medium-sized squares corresponding to all combinations of two factors (cubic strength of concrete and reinforcement coefficient). Each of the 25 middle squares, in turn, consists of 25 cells, corresponding to all possible combinations of other factors: the height of the foundation slab and the relative overhang of the cantilever part. Experimental studies were carried out with large-scale reinforced concrete models of foundations on a sand base, which made it possible to study the parameters of the joint operation of the foundation and soil, and to establish geometric and strength factors that play an important role in the formation of the process of brittle destruction of the foundation (overhang of cantilevers, height of the foundation slab, reinforcement, strength of concrete). Materials and methods: Our experimental studies were divided into two phases: 1 – conducting staged experiments on large-scale reinforced concrete models of foundations in order to select four factors, since a greater number of factors introduced into empirical formulas practically does not increase the accuracy of the formulas, but only increases the number and labor intensity of experiments; 2 – study of the influence of the shape of the plot, normal contact stresses and established primary factors on the strength when punching foundations of full-scale dimensions (2x2 m). Staged experimental studies were carried out on a series of three or five identical models of foundations with a plan size of 1x1x0.1 m (height) at different values of the factors under study. The foundation structures are shown in Figure 1. Results: experimental study of the effect of diagrams of contact stresses of sandy soil on the strength of full-scale columnar foundations during punching; identification of real forms of the punching pyramid on full-scale reinforced concrete foundation samples; development of a method for calculating the strength of brittle fracture of columnar foundations on a sand base; obtaining mathematical dependencies of the destructive load on the parameters of the foundation structure; New structural solutions for foundations.

ИССЛЕДОВАНИЯ СБОРНЫХ ЖЕЛЕЗОБЕТОННЫХ НЕСУЩИХ СИСТЕМ С ПЛОСКИМ ПЕРЕКРЫТИЕМ

The paper gives a brief review of existing load-bearing frame systems with a flat bottom edge of the slab, performed using prefabricated reinforced concrete products. The basic provisions and results of field testing of floor elements of the prefabricated reinforced concrete load-bearing frame, which is not widely spread in the Russian Federation, according to patent No. 132814 «Prefabricated Reinforced Concrete Frame» are also described. Research on the existing load-bearing systems with flat bottom edge of the slab was carried out by studying the patent documentation available in the All-Russian Patent and Technical Library; information posted by the authors in open sources, scientific articles by the authors of the load-bearing systems. In-situ tests of the slab elements of the framework according to the patent No. 132814 «Prefabricated reinforced concrete framework» were performed by means of empirical experiment with loading of prefabricated elements according to the considered system of prefabricated-monolithic reinforced concrete construction. During the tests, the vertical displacements of the elements, the appearance and width of their crack opening were measured, and the destructive load was recorded. The safety factor according to GOST 8829-2018 for the tested slab elements was calculated based on the recorded destructive load. The values of destructive load of the slab structures obtained in the test results confirm the reliability of the adopted solutions, which substantiates the expediency of their further development. The safety coefficients of transoms and floor slabs obtained according to GOST 8829-2018 satisfy the strength requirements for building structures.

Experimental study on mechanical properties of pin-trunnion connection nodes of temporary steel brackets for elevated bridges

Currently, the pin connection test exists mainly for unidirectional force loading, while the pin connection of a temporary steel bracket applied to elevated bridges is for bi-directional force. The damage mechanism of the pin connection with bi-directional force is not yet fully understood in research. The effect of the loading direction, single-hole plate end distance and unilateral width ratio a/b, ear plate thickness ratio t1/2 t2, and ear plate shape on the mechanical properties of the pin connection need to be considered. In this study, destructive static loading tests were conducted on eight groups of double-hole pin connections, and the damage mode, bearing capacity, deformation, and strain of the pin connections were determined. The results show that the thickness of the trunnion plate primarily controls the damage mode of the pinned connection and the ratio is smaller for single-trunnion plate damage, which can achieve larger bearing capacity and deformation. The ratio of the end distance of the monocore plate to the width of the single side primarily controls the damage location of the monocore plate, and the ratio varies from large to small, gradually causing tensile damage to the side section, end cleavage damage, and end shear damage. The loading direction has a minor effect on the mechanical properties of the pin connection; however, the tensile deformation is significantly larger than the compressive deformation. By chamfering, the M shape is properly adjusted to optimize the shape of the double trunnion plate, which does not reduce the load-carrying capacity and deformation of the pin connection and can reduce the amount of steel used by 10 %. A comparative analysis of the change in the ear-plate shape before and after the open ear-plate test, determination of the cross-sectional damage location and effective calculation distance b1, and improvement and derivation of a practical method for calculating the load-carrying capacity for engineering are performed, at the same time, it can be applied to projects of different spans, which can greatly improve construction efficiency and reduce labor costs.

Recording of ultra-low frequency electromagnetic emission during loading of a rock sample

The review of publications devoted to the study and features of the registration of electromagnetic emission observed during the loading of samples of rocks, metals, composite materials in laboratory conditions, as well as in areas of disintegration of rock massifs at mining sites is given. Electromagnetic emission observed during the destruction of rock samples in laboratory experiments and field conditions can appear itself not only in the high and low frequency ranges (1000–3·106 Hz and 500–1000 Hz, respectively), but also in the very low and ultra-low frequency (200–500 Hz and 0.01–200.00 Hz, respectively) ranges. However, the overwhelming majority of experimental studies of rock samples under the influence of a destructive load in laboratory conditions are aimed at measuring electromagnetic emission of the high frequency range. An instrumentation and measurement complex is described that allows recording electromagnetic emission in the ultra-low frequency range. The composition of the instrumentation and measurement complex includes magnetic modulation transducers of magnetic induction as magnetic field sensors. The methodology of laboratory experiments on recording electromagnetic signals arising from the influence of an external load on rock samples using an instrumentation and measuring complex is presented. An example of uniaxial loading of a basalt sample is given. When loading the sample under consideration, the amplitude of the electromagnetic emission pulses exceeds the background values of technogenic magnetic noise by two orders of magnitude. The high sensitivity of the magnetic modulation transducer of magnetic induction allows it to be used to register the components of magnetic induction in the process of destruction of rock samples in conditions of interference from technogenic magnetic noise. The results obtained are important for monitoring and forecasting the process of cracking before mining impacts, as well as for studying the geological environment and processes that generate low-frequency electromagnetic emission in the mining areas.

Technology of Manufacturing Hollow Soil-Cement Blocks

The author analyzed technological solutions for the production of blocks from soil cement. It is proposed to make soil cement blocks from portland cement brand 400 in the amount of 20 % of the mass of soil and water. Experimental addition of fly ash to the solution in different amounts depending on the cement content. It is proposed to add ash removed from the Darnytsya thermal power plant, which was sifted through a 4 mm sieve, because the ash contains a significant amount of impurities. The content of inclusions from 1 to 4 mm was up to 40 %. It is proposed to make blocks from soil cement with the addition of fly ash with the aim of improving the thermotechnical properties. It is proposed to make soil-cement blocks with two voids. To ensure high-quality compaction of products in forms, the moisture content of the content for most soils should be within 14–23 %. The maximum force that the sample can withstand was taken as a destructive load. It was decided that the use of fly ash as part of the mixture in the production of soil cement gives a positive effect. With an increase in the period of exposure of samples in water to 90 days, the average compressive strength of soil cement samples without additives and with the addition of the appropriate percentage of fly ash increases.

Selected issues concerning the use of Shredded Rubber Waste (SRW) in binder-bound mixtures

This paper presents the results of a composite consisting mainly of industrial waste bound by a hydraulic binder. The composite consists of unburnt coal-mining slate, shredded rubber waste (SRW), fly ash and CEM I cement. The purpose of using the above components was to protect the unburnt coal-mining slate from the negative effects of water, which causes degradation of the aggregate grain size and significantly affects the load-bearing capacity of the aggregate. This was achieved through the use of a binder consisting of shredded waste rubber, fly ash and cement, which imparts hydrophobic properties to the composite. The composite is to be used in road pavement construction and earthworks as a substitute for standard materials. This paper focuses on testing the effects of 5, 10 and 15% additions of shredded rubber waste (SRW) on the physical and mechanical parameters of the composite, mainly compressive strength, water absorption by mass, capillary rise and deformability under cyclic loading. The composite was tested under cyclic loading conditions using a measurement system based on digital image correlation (DIC), with which the deformations occurring on the surface of the test specimens were determined. The results obtained showed the influence of shredded rubber waste additives on the decrease in compression strength (after 7 and 28 days of specimen care), mass water absorption and capillary rise, as well as an increase in the deformability of the composite under destructive loading and cyclic loading.

Multi-Story Volumetric Blocks Buildings with Lower Frame Floors

This article presents the results of experimental studies of the stress–strain state of volumetric blocks based on the underlying frame structures. The aim of the research is to evaluate the stress–strain state and the nature of damage development as a result of an increase in the load up to a critical level. Based on the analysis of the nature of the damage, recommendations have been developed to strengthen the destruction zone. Data were collected on the redistribution of stresses and deformations, the formation of cracks and joint openings, the magnitude of horizontal displacements, and the failure mode of volumetric blocks and floor frames. Five full-scale volumetric blocks were tested under the loading of hydraulic jacks, differing in concrete type, reinforcement, presence of doors, and dimensions of the stylobate beams. When the volumetric modules were supported by a frame floor the results revealed that the maximum destructive load of 10,462 kN was observed in the first specimen; the horizontal displacements of the walls decreased by 13–18 mm, and there was a decrease in the crack opening width to 0.5 mm. The cracks decreased the strength of the walls, leading to a redistribution of the compressive stresses and their increase in the support zone. The most significant compressive strains in concrete in the corner parts of longitudinal walls were in the range of (600–620) × 10−6, and in the middle part of the walls, 370 × 10−6 were observed. Furthermore, the largest cracks caused significant horizontal displacements (deplanation) of the walls, which decreased the stiffness of the conjunction of longitudinal walls with the floor slab and created an additional eccentricity of the vertical force. Based on the findings, the correlation between the measured parameters of each specimen at all stages of vertical load increase is demonstrated and illustrated in graphs of the measured parameters. The importance of quantity compliance with the initial rigid connection between the longitudinal wall and ceiling plate has been estimated.

Damage characteristics and dynamic responses of high arch dams under rockfall impact loads

Rockfall is a typical natural disaster that is sudden, high in speed, unpredictable, and can easily adversely affect the structures. High arch dams are usually constructed in deep valleys, where rockfall is a typical destructive load. However, there is currently a lack of research on the effects of rockfall on the safe operation of high arch dams. Therefore, the Wudongde arch dam in China is selected in this paper for exploring damage characteristics and dynamic responses of high arch dams under rockfall impact loads. To improve the authenticity of numerical simulation, a coupled model is established based on the actual dam shape and terrain characteristics of the dam. The concrete damaged plasticity model is used for dam concrete and the rockfall is described by the JH-2 model to simulate mechanical properties of materials and reflect strain rate effects. The trajectories of falling rocks at the dam site are first investigated to analyze the locations where they may impact the dam. Based on the obtained results, two impact positions are considered possible in the analysis, namely, the dam crest and the gate slot, and then the nonlinear dynamic responses of the dam impacted by rockfall at different positions are compared. Finally, a sensitivity analysis is carried out to evaluate the influence of the rockfall properties on the damage characteristics of the dam. The results indicate that the trajectory and impact velocity of falling rocks are related to the falling height, rock size, and initial velocity. The rockfall impact on the dam crest has little influence on the safety of the dam for the robust mass dam concrete, while the track beam near the gate slot is vulnerable to rockfall impact. The damage degree to the structure is related to rockfall properties. Compared to larger-sized rockfalls, rockfalls with a diameter of 1 m cause minimal damage to the structure and have little impact on its safety. Higher impact velocity and stiffness of the rock lead to more severe damage, while the effect is relatively smaller compared to the rockfall size. The high stiffness also reduces the damage to the rock itself.

Poisson's ratio testing method and multi-factor influence quantification model of asphalt pavement materials

The current standard in China does not specify the standard test method for determining Poisson's ratio, and the Poisson's ratio used in pavement design is often roughly fixed, which can result in large errors in the calculations and analysis of road structure. In this paper, the research on different test methods for Poisson's ratio is carried out and the non-linear characteristics of tensile and compressive Poisson's ratio on pavement materials under different influencing factors are analyzed. The results indicate that the absolute value of the ratio between transverse rebound strain and longitudinal rebound strain under 50% of the maximum destructive load can objectively characterize the mechanical properties of Poisson's ratio, and it is the optimal measurement method for Poisson's ratio in asphalt pavement materials. The Poisson's ratio of two pavement materials both decreases with the increase of loading rate and gradually tends to a constant value. Cement dosage and temperature are the most significant factors affecting the tensile and compressive Poisson's ratio of cement stabilized crushed stone and asphalt mixture, respectively. Specifically, when cement dosage increases by 1%, the Poisson's ratio of cement stabilized crushed stone decreases by approximately 10%, and the temperature has a significant influence on the difference in tension and compression for Poisson's ratio of asphalt mixture (up to 40%). The asphalt content corresponding to the minimum Poisson's ratio is basically consistent with the optimal asphalt content obtained by the Marshall volume method. Based on these, a quantification value-taking model is established of the tensile and compressive Poisson's ratios of typical asphalt pavement materials varying with multiple factors. The research results can serve as a reference for the scientific value-taking of pavement structural design parameters considering the different mechanical characteristics of materials in tension and compression.

Determination of soya grain strength, reduction and loss in storage and processing

This scientific article analyzes, that with an increase in soybean production, an important role is given to reducing the loss of soybean grain per harvester and from crushing, when the plants are harvested, and post-harvest processing of grain in the production of reproductive seeds. The studied climatic conditions of the Amur region during the soybean harvesting period (October) are characterized by low precipitation and low relative air humidity, it helps dry the plants. Identified, that under these conditions, soybeans and grain are losing strength and, under the influence of the working bodies of motovil and reaper, beans are pulled off or uncovered and grain losses are noted, a threshing and separation devices (MSU) of a grain harvester crush grain when milled, resulting in crop losses. Formulated in the process of scientific research, that the tensile strength or destructive load of soybean kernels by grade at humidity 6,5% change from 13.03 before 29.02 kg. Knowing the destructive load for soybean grain, proposal for Action, prevent destructive modes of operation for the working organs of the threshing and transporting devices of the combine. Based on the reliably obtained regression equation, the response surface is represented, determining the force of the action of the working bodies of the combine in the function of the changing speed from 8.0 before 20 m/s, mass of grain from 0.15 before 0.35 g., which in the September variety increases to 10 N.

ЕКСПЕРИМЕНТАЛЬНІ ДОСЛІДЖЕННЯ СЕРІЙНОЇ ДОРОЖНО-АЕРОДРОМНОЇ ЗАЛІЗОБЕТОННОЇ ПЛИТИ

The results of experimental studies of the load-bearing capacity and crack resistance of the serially produced road-airfield reinforced concrete slab PAG, manufactured at Velikodolinsky Reinforced Concrete Plant LLC by order of the Odessa State Academy of Construction and Architecture, are presented. In accordance with the regulatory documents in force in Ukraine, one of two possible loading schemes was considered ― with a load by a concentrated force applied on the cantilever part of the slab. The slab was tested on a specially made stand, which consists of four support posts connected in pairs by beams on which the slab rested. The load was applied along the width of the slab in steps ― 0.04 from the destructive load, along two concentrated vertical stripes. Each load stage ended with a five-minute hold, at the beginning and end of which readings were taken on the measuring instruments. All tests were carried out using two 30t jacks and a 50t dynamometer. The principle of operation of the jack was that its lower plane pressed on a two-level cross-beam system, and through it the load was distributed onto the slab. During testing, the applied load, deflections and deformations were recorded on the slabs. Dial indicators and deflectometers were used as measuring instruments. The process of crack formation on the surfaces of the slabs was observed using a Brinell tube in the places of the greatest opening of the cracks. As a result of the tests, the load-bearing capacity of the slab was 163.2 kN with a bending moment of 78.3 kNm. The load corresponding to the onset of cracking is 86.4 kN with a bending moment of 36.9 kNm. The maximum crack opening width was 1.0 mm. Based on the indicator readings, graphs of the dependence of relative deformation on load were constructed. Graphs of the dependence of deflections on load are constructed using data from two deflection meters. Before the first crack appears, the maximum deflection of the slab is 12.0% of the deflection recorded at the end of the tests.

EXPERIMENTAL STUDIES OF SERIAL REINFORCED CONCRETE PAG SLAB WITH ADDITIONAL STEEL FIBER REINFORCEMENT

Thus, in laboratory conditions, experimental studies of the bearing capacity and crack resistance of a serial PAG plate with additional steel fiber reinforcement in the amount of 1% were carried out. In accordance with the regulatory documents in force in Ukraine, one of two possible load schemes was considered ― when loaded by a concentrated force applied to the cantilever part of the slab. The plate was tested on a specially made stand consisting of four support racks connected in pairs by beams on which the plate rested. The load was applied across the width of the slab in steps of 0.04 from the destructive load, in two concentrated vertical strips. Each level of load ended with a five-minute exposure, at the beginning and end of which the readings on the measuring devices were taken. All tests were carried out using two 30-ton jacks and a 50-ton dynamometer. The working principle of the jack consisted in the fact that its lower plane pressed on a two-level cross-beam system, and through it the load was distributed on the slab. In the process of testing the plates, the applied load, deflections and deformations were recorded. Clock-type indicators and protractors were used as measuring devices. The process of crack formation on the plate surfaces was observed with the help of a Brinell tube in the places of the largest crack opening. 
 As a result of the tests, the bearing capacity of the plate was 211.2 kN with a bending moment of 101.4 kNm. The load corresponding to the beginning of crack formation is equal to 96.0 kN at a bending moment of 46.1 kNm. The maximum width of crack opening was 0.25 mm. According to the readings of the indicators, graphs of the dependence of the relative deformation on the load were constructed. Graphs of the dependence of deflections on the load, constructed from the data of two deflection gauges. Before the appearance of the first crack, the maximum deflection of the plate is 17.0% of the deflection recorded at the end of the tests.

Multi-indicator optimization of riveting joint forming quality of aluminum alloy sheets based on response surface test

In this paper, the effects of the interaction between punch diameter, die depth and punch speed on the quality of riveted joints are investigated using the BBD response surface test method. The results show that the mold depth has the greatest influence on the key dimensional parameters of riveted joints, followed by the punching speed, and then the punch diameter, while the punch diameter and the mold depth are the two factors with the most obvious interaction. The optimum riveted joint process parameters determined are punch diameter of 5.24 mm, die depth of 1.44 mm, and stamping speed of 5.00 mm/s. The corresponding relative errors predicted by numerical simulation and response surface optimization objective are 5.96 % for neck thickness, 3.29 % for interlocking value, and 1.37 % for bottom thickness; and the relative errors predicted by experimental results and optimization objective are 13.42 % for neck thickness, 13.42 % for interlocking value, and 1.37 % for bottom thickness. 13.42 %, interlock value is 4.23 %, and bottom thickness is 2.23 %, the model accuracy is high, and the optimization method of response surface test can effectively improve the quality of riveted joints. Through numerical simulation, the metal flow law and stress distribution during the riveting and forming process of aluminum alloy plate were analyzed, and the strength test of riveted joint was carried out, and the maximum destructive shear load of the joint was 1.8 KN, and the strength of the joint was improved, which verified the validity of the response surface optimization method.

Технология изготовления образцов из полимерных композиционных материалов

The article considers the materials, composition and methods of manufacturing samples from polymer composite materials (PCM). There is presented the method of testing samples of PCM for mechanical properties. For testing, plates were made from which samples from PCM were cut, based on glass roving, glass wool and polyester resin with the addition of a hardener. Using mechanical tests, the influence of the quantitative ratio of layers of glass wool and roving fiberglass has been determined when testing samples for three-point bending, stretching and compression. A scheme of structural reinforcement of PCM plates is given, graphs of the average values of breaking loads and ultimate strengths when testing samples for three-point bending, dependences of average values of breaking loads and ultimate strengths when testing samples for tension and compression are illustrated. Comparative analysis of the average values of the tensile strength of the samples during the compression test has been carried out. As a result of processing the data obtained during the study, it was found that with an increased number of layers of roving glass in the PCM composition increases the destructive load and tensile strength, compression, but the values of the applied load of PCM samples decrease during three-point bending tests. The experimental data obtained from the test results of PCM samples are the main indicators of the mechanical properties of PCM with various reinforcement schemes for their use in ship hull structures, in particular as a material for ship tanks.

Influence of Layer-Thickness Proportions and Their Strength and Elastic Properties on Stress Redistribution during Three-Point Bending of TiB/Ti-Based Two-Layer Ceramics Composites

A mathematical model was developed to determine the order of failure of layers in a two-layer ceramics composite and to determine the conditions for achieving the maximum limit load under three-point loading. The model was set in the space of three “bilayer parameters”: the ratio of the thickness of the lower layer to the whole thickness of the beam, the ratio of Young’s moduli of the lower layer to the upper layer, and the ratio of flexural strengths of the materials of the lower layer to the upper layer. The adequacy of the model obtained was confirmed by experimental results on the three-point bending of the experimental specimens. The experimental samples were two-layer composites consisting of a cermet layer TiB/Ti and a layer of α-Ti. The samples were obtained by free self-propagating high-temperature synthesis (SHS) compression and with varying their thickness. The results obtained make it possible to predict in advance which layer, based on the specific bilayer parameters, will trigger the brittle fracture mechanism as well as to set the maximum destructive load of bilayer composites.

Wind loads tests of external walls blocks masonry of noncombustible polystyrene concrete

Introduction. Blocks of non-combustible polystyrene concrete of D300 density grade, B1 compressive strength class with normalized thermal conductivity λ0 = 0,078 W/(m·°C) and frost resistance grade not lower than F75, developed by LLC “Institute VNIIZhelezobeton”, were used in masonry with a thickness of 375 mm without special fireproof lining. Such masonry successfully passed standard fire tests for fire hazard and fire resistance, which showed the possibility of its use in external non-bearing energysaving walls of multi-storey buildings (up to 25 floors inclusive, about 75 m high).Aim. Evaluation of the strength and deformation characteristics of non-combustible wall masonry made of noncombustible polystyrene concrete blocks with a density of D300 at design wind loads at a height of about 75 m. Materials and methods. Fragments of uncoated wall masonry 375 mm thick, 2,7 m high and 1,2 m wide of noncombustible polystyrene concrete blocks mounted on a mortar with over-all dimensions of 295 × 375 × 595 mm were tested.The test procedure is in accordance with State Standard 8829-2018.Results. The destructive bending load exceeded the calculated one by an average of 4,1 times, while the deflection in the middle of the fragment was 1,9 times less than the permissible one.A methodology has been developed for calculating the strength and deformability of masonry of polystyrene concrete blocks under wind loads, taking into account the influence of horizontal and vertical masonry joints, which is scheduled to be reflected in Amendment No. 1 SP 434.1325800.2018.Conclusions. The results of wind load tests showed that for unlined masonry made of non-combustible polystyrene concrete blocks with a density of D300 and a thickness of 375 mm, the requirements for strength and deformability are met with a significant margin. The results of tests for wind and fire effects of the specified block masonry make it possible to use it in nonbearing external walls of multi-storey residential energyefficient buildings up to 75 m high in virtually all regions of Russia.