Strength Margin Research Articles

Operating Load of Belt Conveyor as a Reflection of Actual Planogram of Coal Shearer Operation in Integrated-Powered Face

Conveyor transport at a modern coal mine is the main link that determines the overall performance of the enterprise. For safe operation of belt conveyors, it is important to ensure that shift output per face doesn’t produce average and maximum minute material flows, which exceed strength margin of the belt, power margin of the drive, and receiving capacity. Such situation, as a rule, may arise due to the strive of workers to compensate for underproduction caused by long downtimes of a face for any reason. In the paper, a method is proposed that enables determining the maximum shift output per face. According to the technique described in the “Basic Provisions for Designing Underground Transport of New and Existing Coal Mines,” the average minute material flow, which determines the operational load on a belt conveyor, depends on the material feed time factor. Accepting the assumption that a coal shearer works the entire shift in a face, the limiting value of the material feed time factor is equal to 1. To determine the actual value of this factor, it is proposed to determine the face operating (production) time using actual planogram. The shift time is spent for preparatory and finishing operations, the face equipment and conveyor line troubleshooting and failure recovery, auxiliary service operations and, finally, operational and organizational downtimes. On the actual planogram, these time intervals are displayed by straight-line portions. Thus, the shift time minus downtime for any reason, represents the face production time. The ratio of these values represents the operation factor. Applying the operation factor allows to determine the maximum limiting face production, not only taking into account the volume of coal mined per cycle, but also based on coal cuttability and technical specifications of the face equipment. This enables us to determine the face production load that ensures safe operation of the belt conveyor.

Investigating the strength and deformability of the node that connects precast slabs and monolithic joists in a flat precast-monolithic flooring slab

The paper reports a study into the strength and deformability of the node that connects precast slabs and monolithic flooring joists in a flat precast monolithic floor based on the work of dowel pins. Current regulations for the design of reinforced concrete structures do not take into consideration the calculation of nodes that connect precast-monolithic structures in flat floors using dowel pins. We have devised a procedure of experimental research that accounts for the specificity in the operation of a precast slab that forms a floor's part. It was established that a change in the type of supports changes parameters for the stressed-strained state of samples of a precast monolithic floor slab: relative deformations of concrete, deformations of samples, as well as strength.Testing the samples of a precast monolithic floor slab has demonstrated reliable operation of both the junction and the normal cross-section of the slab. It was determined that the node that connects precast multi-hollow slabs and a monolithic flooring joist using dowel pins has a 1.42-fold strength margin. The paper reports results from field testing a fragment of the frame of a building for the influence of vertical loads. It is shown that the development of deformations in the main bearing elements of a floor slab occurred almost in line with a linear dependence; they amounted to 18.55 mm (for the central precast slab of a floor slab's center) and 14.64 mm (for the bearing flooring joist). These deformations are more than 2 times less than the permissible value for vertical deformations (deflection) for these elements, which is equal to 40 mm.The results from field testing have led to a conclusion on that the precast and monolithic elements in the floor slab's disk operate as a solid structure. The tests did not detect any mutual displacements of the side ends of precast slabs relative to the load-bearing flooring joists. The procedure for calculating the strength of the connecting node has been improved. A change in the strength of samples of a flat precast monolithic floor slab is accounted for by the introduction of an appropriate coefficient for the operation conditions of transverse reinforcement, which is equal to 0.8.

Effects of Hooked-End Steel Fiber Geometry and Volume Fraction on the Flexural Behavior of Concrete Pedestrian Decks

This study investigates the effects of hooked-end fiber geometry and volume fraction on the flexural behavior of concrete pedestrian decks. To achieve this, three different fiber geometries, i.e., three-dimensional (3D), four-dimensional (4D), and five-dimensional (5D), and volume fractions of 0.37%, 0.6%, and 1.0% were considered. Test results indicate that a higher number of hook ends can more effectively enhance the flexural strength and flexural strength margin at all volume fractions than a lower number, so that the order of effectiveness of hooked-end fibers on the flexural strength parameters was as follows: 5D > 4D > 3D. To satisfy the ductility index of 0.39, the amounts of 3D, 4D, and 5D hooked steel fibers should be in the range of 0.98%‒1.10%. Moreover, at a fiber volume fraction of 1.0%, only multiple cracking behaviors were observed, and the numerical results indicated that the volume fraction should be equal to 1.0% to guarantee a deflection-hardening response of pedestrian decks, regardless of the hooked-end fiber geometry. Consequently, a 1.0% by volume of hooked-end steel fiber is recommended to replace the minimum longitudinal steel rebars and guarantee a ductile flexural behavior with multiple cracks for pedestrian decks made of high-strength concrete.

Методология определения ресурса работоспособности РДТТ с учетом запасов прочности материалов и элементов

Методология определения ресурса работоспособности РДТТ с учетом запасов прочности материалов и элементов

Experimental Study of the Biomechanics of Maxillary Implants under Conditions of Biomechanical Modeling.

We studied the stress-strain state of the bone tissue and maxillary full-arch fixed implantretained denture. Load was applied to the anterior (150 N) and posterior (250 N) parts of the denture supported by 6 or 4 implants, including zygomatic ones and placed by on-all-4 treatment technology. The obtained stress values in the bone tissue, implants, and denture show a large strength margin of structural materials. At the same time, the bone strength values were low, especially around the zygomatic and distal implants of all-on-4-implants-supported dentures when the posterior part of the denture was under load.

Geometry of Hollow Polymer–Composite Shafts for Power and Torque Transmission

The stress and strain in the torsion of hollow polymer–composite shafts transmitting torque may be calculated from the motor power and speed, taking account of the mechanical properties of the polymer composite and the margin of strength.

РЕАЛІЗАЦІЯ ПРИНЦИПІВ ZERO WASTE В МЕХАНІЗМІ РЕСУРСОЗБЕРЕЖЕННЯ В СІЛЬСЬКОМУ ГОСПОДАРСТВІ

Introduction. Target priorities for accomplishing resource conservation tasks in agriculture require conceptual framework in order to determine the driving principles of taking effective measures in practice. As the problem of resource conservation is rather complicated, the implementation of resource conservation policy involves overcoming a number of existing organizational and economic problems, which updates the topic of the research. The purpose of the article is to explore the possibilities of implementing Zero Waste principles in the resource conservation mechanism in agriculture. Results . Basic concepts and theoretical models of resource conservation have been considered. The focus is on the Zero Waste concept, which involves : zero discharge, zero emission, and waste reduction to zero. The downside of the Zero Waste concept is that it focuses mainly on the environmental parameters of investing in the resource conservation technologies, while the enterprise is primarily interested in the profit s from them. The author proves the necessity for expanding the concept line with a specific to the agrarian complex concept of organic farming based on the agrobiological concept of farming . The place of organic agriculture in the system of multifunctional resource conservation agrarian production and ways of achieving the main goals of resource conservation organic farming are presented. Originality . Taking into account the effectiveness of the concepts of introduction of resource conservation systems of management it was proved that the main task is making scientific and technological advances in agriculture, as well as develop ing and implementi ng the mechanisms for the introduction of their elements, which in the future should change the concept underlying the resource conservation economy. The author has systematized the elements of the economic mechanism of resource conservation , the role of which is to create an environment for the interaction of the key components of agriculture in the system of the efficient resource conservation production. The experience of developing an effective practice of resource conservation in agriculture was generalized and the principles of harmonization of the management system were defined. A model scheme of the economic mechanism of resource conservation in agriculture has been developed, based on four subsystems that reflect the sources and target directions of the information , tangible and intangible flows: innovation field, functional basis (market environment and resource base), production subsystem (crop production and animal husbandry) , as well as the strategic core of the management system. It is proved that a prerequisite for the development of the system of agricultural resource use is availability of an appropriate functional basis, provided by the solvent demand from the market environment , and an appropriate resource potential of a natural origin , to create economically advantageous conditions for the development of agriculture. It is the needs of the market environment that are decisive in shaping the conditions of establishing and develop ing relevant agricultural sectors in the region concerned. The r esource potential appears to be an appropriate equalizer of competitive conditions, providing economic entities with a margin of economic strength in shaping their competitiveness. Using the proposed architecture, the scheme of the mechanism of resource conservation in agriculture in the innovative field of the Zero Waste concept was devised . Conclusion . It is concluded that the management of resource conservation in agriculture should take into account the general principle of nature management; the principle of replacing material and energy resources with intellectual and organizational ones; the principle of interconnectedness and synchronization of process es ; the principle of the proportionality of the processes of evolutionary and revolutionary approaches in the innovative provision of resource conservation processes; the principle of the need to ensure the long-term and systematic development and build-up of resources, their transformation into knowledge and their effective management, form ing the basis of the proposed mechanism of resource conservation in agriculture in the innovative framework of the Zero Waste concept.

SEMIOSPHERE OF CULTURE OF GENTRY’S ENVIRONMENT AND ITS DYNAMICS IN THE EARLY XX CENTURY

This article is about the semiosphere of culture, which was determined by the famous cultural scholar and philosopher Yuriy Lotman. In his works he developed the concept of the semiosphere of culture, conditions of transformation and dynamics of its semiotic borders. Semiosphere of culture is inherent among different team groups, classes, fractions (gentry is included), which at the turn of the XIX - early XX century experienced a number of changes and transformations. During this period the membrane of gentry’s culture was flexible and sensitive: it interacted and affected the formation of ethos of the bourgeoisie’s and the intelligentsia’s culture, changing its semiotic borders. The main functions of the semiotic border (to separate, to guard and to preserve) have been weakened, because the growing ossification and the hardiness in the new modern circumstances would have doomed the gentry’s culture to destruction. In return, the function was to detach, to detect similar and non-similar features, to create new ideas, texts and languages with the other team groups that are close in the footsteps and values. Gentry’s environment due to the process of urbanization and modernization dropped out from the “closed-system” centuries, has become more elastic to the other layers of society, in particular, to the wealthy bourgeoisie in the Western Europe. In Galicia, the gentry of Russian origin were transformed into the Greek Catholic clergy, which brought up a nationally conscious secular Ukrainian intelligentsia during the following generations. Because of the social transformations of the late XIX – early XX centuries, gentry disappeared, its titles and privileges were officially abolished, but the basic factors of its ethos became a part of the semiosphere of the burghers, clergy and intellectuals. Since culture develops with a certain inertial margin of strength, Ukrainian intelligentsia for a long time during the twentieth century enjoyed a cultural capital and a sense of duty, responsibility and self-sacrifice, taught by its predecessors. The revision of the attitude to the Ukrainian gentry as spiritual elite in Ukraine means a change in the national historiography and paradigm of cultural memory.

Modal analysis of impact test platform

In this paper, the impact dynamics and nonlinear finite element method are analysed systematically. The static analysis of the test platform was carried out, and the result of the static analysis showed that the stress concentration existed in the connector and it had a large strength margin. Modal analysis is carried out on the test platform. Through modal analysis, the natural frequency of the test platform is obtained. The impact load response is determined to be the category of complex impact by comparing the impact loading time of the hammer system.

Effect of steel fibers on the flexural behavior of RC beams with very low reinforcement ratios

This study aims to investigate the implications of hooked-end steel fibers on the flexural performance of reinforced concrete (RC) beams with very low reinforcement ratios. For this, four different fiber volume fractions, vf, of 0.25%, 0.50%, 0.75%, and 1.00%, were incorporated into the concrete mixture and plain concrete without fibers was considered as a control specimen. Four reinforcement ratios of 0.178%, 0.267%, 0.317%, and 0.406%, which are 44%, 66%, 78%, and 100% of the minimum reinforcement ratio, ρmin, were also adopted to evaluate the steel fiber effect on the flexural behavior of RC beams with various very low reinforcement ratios. The test results indicated that the overall flexural performance of RC beams, in terms of flexural strength, deflection capacity, post-cracking flexural stiffness, and cracking behavior, was improved by increasing the reinforcement ratio up to ρmin. Higher initial cracking and yield loads, post-cracking stiffness, and better cracking performance of RC beams were also obtained by including steel fibers. However, the enhancement of ultimate load carrying capacity by steel fibers was relatively minor, and the ductility index and flexural strength margin, used to guarantee a ductile failure mode, deteriorated with the inclusion of steel fibers. The lower reinforcement ratios and higher fiber volume fractions clearly led to lower ductility indices. Therefore, it was concluded that longitudinal steel rebar could not be replaced with discontinuous steel fibers at moderate volume fractions, vf ≤ 1.0%, in terms of ultimate load carrying capacity, ductility, and flexural strength margin. Lastly, analytical results considering material models for steel fiber-reinforced concrete (SFRC), given by the RILEM recommendation, generally overestimated the flexural capacities of reinforced SFRC beams, and the inaccuracy increased with increasing fiber contents.

Estimation of carrying capacity of metallic corrugated structures of the type Multiplate MP 150 during interaction with backfill soil

We estimated the stressed state of a railroad structure with a large cross section spanning more than 6 m, which is made from metallic corrugated sheets of the type Multiplate MP 150. The stressed-strained state of the corrugated structure was estimated depending on the residual deformation of vertical diameter of the pipe, the modulus of elasticity of backfill soil, and the degree of compaction. The study conducted has demonstrated that maximum stresses occur on the horizontal sides of a metallic pipe, and maximum deformations – in the pipe vault. It was established that an increase in the degree of compaction of backfill soil leads to a decrease in the stresses in a metallic pipe by almost half. The stresses grow much faster with an increase in irregularity on the railroad track. Numerical calculations have shown that the equivalent stresses exceed the permissible magnitude of 235 MPa when the degree of compaction of backfill soil is below 90 % and an operational irregularity on the track develops beyond the permissible magnitude. Operational observations have shown that the pipe is most vulnerable, in terms of resistance against the formation of a plastic hinge, in the initial period of operation when the backfill soil has not yet reached the standard compaction. At the initial stage of operation of a metallic corrugated pipe it is necessary to improve the level of technological control in order to timely detect railroad track’s irregularities that exceed the standards, and to eliminate them. Under normal operational conditions, a metallic corrugated structure has a rather large reserve of carrying capacity, which amounts to 80 %. However, these structures, despite their high initial strength margin, are very sensitive to an increase in external dynamic loads due to the occurrence of irregularity on the railroad track.

RESOURCE–SAVING RESERVE OF STRENGTH CHARACTERISTICS OF LONGITUDINAL BEAM OF THE METRO WAGON TRUCK

In this paper, an analysis of methods for calculating structures from allowable stresses and from limiting states is made. It is shown that when the transition from the longitudinal beam calculation to the allowable stresses to the calculation of the limiting state, the strength limit increases by 1.5 times. A mathematical model of the stress–strain state of a longitudinal beam of metro wagon truck without taking into account the transverse force is developed. The mathematical modeling with the given margin of strength of the power calculation of the longitudinal beam metro wagon track, which is a simple beam of a constant hollow rectangular section, pinched at its ends and loaded along the middle of the span by a concentrated stationary force, is carried out. Thus, the application of the method of calculation for the limiting state makes it possible to identify the resource–saving reserve of the strength characteristics of the longitudinal beam of the metro wagon truck – a 3-fold increase in the maximum permissible load.

Biomechanics of implant retained fixed prosthesis in patient with edentulous upper jaw

The purpose of the study was to study the stress-strain state of bone tissue and a permanent prosthesis on implants installed in the frontal part of the upper jaw. The 150N load was applied to the frontal and 250N to the side of the non-removable prosthesis on six or four implants, including zygomatic and 'All-On-Four' technology. The values of stresses in bone tissue, implants and prosthesis are obtained, which show a large margin of strength in structural materials. At the same time, the bone strength is low, especially around the zygomatic implants and the extreme implants 'All-on-4' with the load of the lateral part of the prosthesis.

Strength and durability analysis of a flat spring at vibro-impact loadings

Volodymyr Gursky, Igor Kuzio We present the scheme of realization of a vibro­impact system with one flat spring and locally focused mass. The means of implementation of asymmetric piecewise linear elastic characteristic is the use of two intermediate cylindrical supports. We calculated the bending and contact stresses that take into account the asymmetry of change in the elastic characteristic and instantaneous displacement of the local mass. The parametric dependency is taken into account of the contact rigidity between the cylindrical support and the flat spring on the displacement of the local mass. This is carried out in order to assess in the course of dynamic analysis the stressed state of a flat spring under conditions of implementation of elastic characteristic. The contact rigidity is taken into account through the change in own oscillations frequency of the spring. We numerically solved the dynamic problem and obtained the ratio between kinematic characteristics (displacement and acceleration) and parameters of the stressed state (bending and contact stresses). The contact stresses are nonlinearly dependent on displacement, the bending –linearly. The strength margin factors by the stresses were defined, as well as the equivalent strength margin factor and the lifetime of the rod as the function of effort of perturbation. The equivalent strength margin factor takes into account the joint action of bending asymmetric and contact stresses. The obtained formulas realize the method of analysis of the stressed state under conditions of vibro­impact loadings. The method may be successfully applied in the course of design and synthesis of resonant vibro­impact systems and modes.

Some Aspects of Inclusion of Loading History in the Fracture Strength Analysis of Reactor Pressure Vessels Under Thermal Shock Conditions

The paper addresses some aspects of inclusion of loading history in the fracture strength analysis of reactor pressure vessels under thermal shock conditions. The strength assessment of a reactor pressure vessel and its lifetime extension are shown to essentially depend on reliability of results of elastic-plastic modeling of stress-strain kinetics and determination of design values of the fracture mechanics parameters. The present findings of the finite-element analysis demonstrate that the loading history must be taken into account in the determination of the temperature dependence of stress intensity factor for a postulated specified crack. It is shown that, in the fracture toughness analysis of a reactor pressure vessel, the temperature dependence of the stress intensity factor has to be derived from the results of the analysis of kinetics and mode of loading of metal at the crack tip under thermal shock conditions. For construction of the above dependence, we proposed approach, which accounts for the active loading and unloading processes occurring in the metal in the crack front vicinity. Incorporation of the loading history into the analysis of the temperature dependence of the stress intensity factor using the proposed approach forcan permit revealing some additional margin of strength during the substantiation of lifetime extension for a reactor pressure vessel under thermal shock conditions.

Evaluation of the Residual Life of the Casings of Steam Turbines Used by Nuclear Power Plants (NPP)

The experience of the operation of nuclear power plants allows us to substantiate the revision of earlier specified lifetime for the power units of nuclear power plants. In December 2016 the specified lifetime expires for the power unit No3 at the Rivne NPP equipped with the reactor of a BBEP-1000 type and the turbine К-1000-60/3000 and the residual life of the equipment must be evaluated to provide a reliable operation for new power units and the reduction of the expenditures for putting them into the operation. The purpose of this scientific paper is to extent the operation life for the power equipment. For structurally complicated HPC casings three-dimensional structures with horizontal flanges, steam supply pipe branches and other elements are taken into account. The methods were developed to create dimensional analogues of the elements of turbine machines using Solidworks software product for the HPC casing. The geometric model was constructed on the basis of the certificate drawing for the К-1000-60/3000 turbine. A maximum intensity value of conventional elastic stresses caused by a difference in the temperature and steam pressure in HPC is observed in the steam inlet zone near the flanges and it is equal to σ імах = 526 MPa in the case of cold start. A reduced deformation of casing is 0,0018 % in the case of cold start (CS) at a time point of 1800 s and it is equal to 0,00276 % in the case of hot start (HS) at a time point of 360 s, which corresponds to allowable norms of 0,09 %. A maximum temperature gradient in the case of hot start arises in the HPC for all control units at a time point of 360 s. Extension of the operation life of power equipment was substantiated by carrying out computing investigations of the thermal state and the mode of deformation and the evaluation of the residual life of the HPC casing of the steam turbine К-1000-60/3000 for the power unit of 1000 MW ²Rivne NPP² owned by the state company ²Energoatom². The estimated life of the casing metal for the high pressure cylinder of steam turbine К-1000-60/3000 is worked out by 10 %. The margins of statistical strength of the HPC casing are everywhere within allowable limits. The individual residual life of the casing of high pressure cylinder of the steam turbine К-1000-60/3000 is 272676 hours that allows us to extend the term of operation for 10 years taking into consideration reactor operation conditions.

An imitation model of a power-supply system of oxygen-converter manufacturing to analyze switching overvoltage

This paper considers switching overvoltage that occurs in the power-supply system of oxygen-converter manufacturing when a circuit vacuum breaker is triggered. The particular features of such systems are analyzed, and a typical power supply scheme is considered. It is noted that overvoltage manifesting a highfrequency behavior can be produced as a result of the peculiarities of arc interruption in vacuum (current chopping, voltage escalation, and arc reignition). Such overvoltage negatively affects electric motors with insulation that have the lowest margin of dielectric strength. Conventional means of overvoltage protection—such as conventional spark-gapped arresters, metal-oxide surge arresters, and spark gaps—are inefficient at high-frequency overvoltage because of a sharp increase in their voltage-second characteristics at low pulse duration. This paper suggests using RC circuits as protection from such overvoltage. Their application is accompanied by quite exact simulations since an incorrect choice of their parameters can worsen the commutation process. The main particular features of construction of a simulation model to study switching overvoltage and to analyze protection functioning are considered. A depiction of the simulation model and results of simulations are also presented. The validity of the suggested model is determined.

Estimation of Some Admissible Deviations from Design Size and Location of Structural Elements of Quick-Release Fasteners of Natural Gas Cleaning Filter Separators

An estimation of admissible deviations of size and location of structural elements of quick-release fasteners of natural gas cleaning filter separators from the design is given. A generalized computational model for analyzing stress-strain state and strength of cheeks of securing unit of quick-release fasteners with deviations is substantiated. Stress-strain and strength analysis revealed insufficient strength margin of the cheeks in the most stressed section. A method is proposed for strengthening the cheeks without disassembling the securing unit, which ensures the required strength margin in this section.

Fatigue Resistance of Reinforcing Steel Bars

During the last few years there has been an intensification of interest in the fatigue performance of steel reinforcement bars in concrete structures. Although fatigue has not proved to be a problem to date, loading cycles are becoming increasingly severe so that the margin of reserve strength is progressively being reduced. In this paper the authors present and discuss results of fatigue life tests performed for reinforcing steel bars which is one of the most widely used construction material in the world. Endurances can be influenced by type of steel, geometry and size of the bars, nature of the loading cycle, welding and presence of corrosion. The experimental part deals with fatigue testing of specimens for identification of the strain-life behaviour of reinforcing bars and determining the number of cycles to failure.

Физико-механические свойства девитализированных ксеноимплантатов на основе перикарда, створок аортального клапана и артерий

Physical and mechanical properties of the tissues of porcine pericardium, aortic valve leaflets and arteries have been studied following devitalization by cryoirradiation method. Low temperatures and ionizing radiation were used for pre-implantation treatment of xenotissues. Uniaxial tension of tissues was tested after freeze-thawing, radiation with flow of electrons, as well as after their combined impact. The extracellular matrix (ECM) of devitalized tissues has been shown to retain its integrity and to possess physical and mechanical properties characteristic for native tissue in both the longitudinal and transverse directions. Pre-freezing to –196°C exhibits a radioprotective effect and eliminates the negative influences of [beta–]-radiation on the ECM. Deep freezing and [beta–]-radiation induce the formation of additional intra- and intermolecular cross-linking as well as demonstrate a synergistic effect: elastic properties of tissues are significantly strengthened. Modified tissue of pericardium, valve leaflets and arteries with pre-determined physical and mechanical characteristics can be used as tissue implants and scaffolds: elastic properties provide lasting existence in a recipient's body (allowing the repopulation and formation of new structure); the strength margin to withstand the operational loads during functioning; preserved carcass ability, elasticity, extensibility, breakage and twisting resistance. Probl Cryobiol Cryomed 2015; 25(4):311-328.