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Niestabilność reologiczna węglanowych mieszanek powlekających zawierających skrobię modyfikowaną

Stanisławska Anna, Gapiński Artur

Przegląd Papierniczy

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2023

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R. 79, nr 2

102--109

PL

Celem niniejszej pracy było zbadanie wpływu dodatku skrobi modyfiko-wanej na stabilność reologiczną mieszanek powlekających zawierających węglan wapnia. Wyznaczone zostały krzywe lepkości i krzywe płynięcia z uwzględnieniem czynnika czasu zarówno dla mieszanek, jak i roztworu skrobi modyfikowanej oraz dyspersji węglanu wapnia. Zawartość skrobi modyfikowanej w mieszankach powlekających wpływa na właściwości reologiczne tych mieszanek, zwiększając ich lepkość i naprężenie ścinające. Wykazano, że mimo reostabilnego charakteru roztworu skrobi i dyspersji węglanu wapnia przygotowane mieszanki powlekające okazały się być płynami reoniestabilnymi. Ich lepkość i naprężenie ścinające zmniejszały się przy wydłużeniu czasu ścinania, co świadczy o właściwościach tiksotropowych. Im większy był dodatek skrobi, tym większa była rozpiętość ramion pętli histerezy krzywych płynięcia i lepkości. A zatem, reologiczna niestabilność mieszanek powlekających wzrastała z dodatkiem skrobi.

EN

The rheological properties of coating color affect its flow behavior during technological process. If upon constant shearing, fluid properties do not change with time, the fluid exhibits rheological stability (rheo-stability). On the other hand, a fluid is said to exhibit rheological instability (rheo-instability) if shear time (for a given shearing conditions) affects its flow behavior. The objective of the conducted research was to examine the effect of modified starch on rheological instability of the coating colors. For this purpose, viscosity curves and flow curves were determined considering the time factor. Such experiments enabled to determine time-dependent rheology. Rheological tests were carried out for calcium carbonate-based coating colors with different starch content (1 pph, 2 pph, 5 pph and 10 pph) as well as for the raw materials used for their preparation, i.e. 10% solution of modified starch and 60% calcium carbonate dispersion. During the research, the rotary rheometer Brookfield RVDV - III+ with the Rheocalc V2.3 control software was used. The measurement principle is based on the determination of the torque for a given shear rate or rotational speed. The measuring element (e.g. spindle, coaxial cylinders), immersed in the test fluid, is set in rotation. A viscous liquid resists the measuring element by generating a torque which is a function of the apparent viscosity of the liquid. During the tests, both RV spindles and DIN coaxial cylinders were used, with the rotating inner cylinder and the stationary outer one. Programs in the B.E.A.V.I.S (Brookfield Engineering Advanced Viscometer Instruction Set) programming language were developed to control the rheometer and collect measurement results. This enabled the experiments to be performed automatically. In order to examine the influence of shear time on the flow and viscosity curves, measurements were made at time intervals of 10, 30 and 60 seconds (the measurement was carried out after 10, 30 or 60 s from the moment of changing the shear conditions, i.e. shear rate or rotational speed). The effect of time on viscosity for constant shear conditions was also investigated. Measurements were made within 4 minutes, and data were collected every 2 seconds. Time factor studies enabled to research rheo-stability and/or rheo-instability (time-dependent rheology). For all tested properties, at least 7 measurements were carried out, and the coefficients of variation did not exceed 4.75%. The starch solution exhibited rheo-stable shear-thinning behavior, whereas calcium carbonate dispersion was a rheo-stable shear thickening fluid. This means that the rheological properties of these liquids depended on shear field but did not depend on shear time (for a given shearing conditions). The content of modified starch in coating colors affects the rheological properties of these liquids, increasing their viscosity and shear stress. It was found that despite the rheo-stable character of both the starch solution and the calcium carbonate dispersion, the prepared coating colors were rheologically unstable as they exhibited time-dependent flow behavior. The viscosity of the coating colors decreased not only with the increase in rotational speed, but also with the increase in shear time. The decrease in their viscosity and shear stress with increasing shear time proves that the tested coating colors exhibited rheo-unstable thixotropic flow behaviors. Additionally, the higher the addition of starch was, the wider was the span of the hysteresis loop arms for both the flow and viscosity curves. Thus, the rheological instability increased with increasing starch content.

2

Behavior study of the steel plate girder with a cellular honeycomb web

Ammash Haider K., Shaffaf Noora N.

Przegląd Naukowy Inżynieria i Kształtowanie Środowiska

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2023

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Vol. 32, No. 2

101--116

EN

Based on the experimental test results of the authors, this investigation is concerned with the finite element analysis to examine and compare the load values and failure modes of the authors’ results. This research was conducted using the Abaqus software. The experimental work included the fabrication of twelve plate girders with honeycomb and flat web plate corrugation patterns, which were then tested under a single concentrated load at the midspan. According to the corrugation dimension or outer honeycomb web thickness, the honeycomb steel plate web girder is divided into three groups (60 mm, 80 mm and 100 mm). The specimens also involved plate girders with a flat web. The specimens were created with three lengths (600 mm, 1,200 mm and 1,800 mm). The Abaqus software was used in finite element models to simulate the concentrated load. The numerical results demonstrated that the 60 mm thick honeycomb web provides a greater load-bearing capacity and shear strength than other girders. The 20 mm honeycomb corrugation on the steel plate girder indicates the increased and improved shear resistance. The conclusion was that as the width of the corrugation increased, so did the steel web’s ultimate load and shear strength, resulting in a positive relationship between the critical shear buckling load of the web and the moment of inertia at the strong axis. When the dimension of the corrugation increases, the moment of inertia of the Y axis (Iy) decreases; thus, the plate girder will fail with a less critical buckling load (Pcr). Also, it can be concluded that as the steel plate thickness of the honeycomb web increases, the shear resistance increases as well. However, the spacing between the intermediate stiffener or the horizontal spacing of the web panel can enhance the shear resistance of honeycomb web girder if it was decreased due to increasing the action of tension field force that resists the diagonal tension developed at the web panel by the applied midspan concentrated force.

3

The Changes of Elongation Index of erythrocytes caused by storage of blood at low temperature

Dylong Iwona, Dolibog Paweł, Mularz Tomasz, Młynarski Jacek, Grzegorczyn Sławomir

Polish Journal of Medical Physics and Engineering

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2023

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Vol. 29, Iss. 1

35--41

EN

Introduction: An important parameter characterizing the ability of erythrocytes to deform depending on the blood flow conditions is the Elongation Index (EI), and it is a parameter defined by the shape of the erythrocyte obtained as a diffraction pattern of erythrocytes at different values of shear stresses. Material and methods: EI measurements at different shear stress were performed by Laser-assisted Optical Rotational Cell Analyzer (LORRCA) for erythrocytes derived from Tissue Bank in Katowice. Measurements were performed immediately after receiving them from Tissue Bank and after 2, 9, and 28 days of storage of samples at the temperature of 4°C in solution with the anticoagulant. Results: An increase in the erythrocytes Elongation Index in the first 9 days of storing samples at low temperatures was observed in the entire range of applied shear stresses. This indicates an increase in the elasticity of erythrocytes during short-term storage at 4°C. In turn, on the 28th day of erythrocyte storage, a significant decrease in the Elongation Index for shear stresses greater than 1 Pa was observed, which indicates the stiffening of the erythrocyte membrane structure, reducing their elasticity. The relative decrease in the Elongation Index of erythrocytes stored for 28 days compared to erythrocytes measured at the beginning was similar and slightly greater than 30% for shear stresses greater than 3 Pa. For shear stresses lower than 3 Pa, the relative change in elongation index was smaller than for shear stresses greater than 3 Pa and increased with the increase in shear stress. Conclusions: The elongation index of erythrocytes stored in the anticoagulant solution at 4°C, initially increases in the entire range of applied shear stresses in the first few days from the moment of blood collection and preparation at the Tissue Bank, and then decreases, but on the ninth day of storage the elongation index is still higher than for blood immediately after collection.

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Rheological behavior of polymer-based drilling fluids: experimental study of temperature effects

Safi Brahim, Aboutaleb Djamila, Haider Soumya

International Journal of Applied Mechanics and Engineering

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2023

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Vol. 28, no. 1

95--104

EN

Drilling fluids most commonly used are generally based on polymers. Polymers such as methylcellulose carboxylate (CMC), polyanionic cellulose (PAC) and xanthan (Xn) have a very important role in the success of drilling operations. Indeed, they are also used to improve certain properties, in particular rheological. However, these polymers can lose their characteristics under the influence of increasing temperature at the bottom of oil wells, thus affecting the ability of the mud to perform its useful role in the drilling operation, namely to raise the cuttings from the bottom of the well to the surface. The present work aims to study the effect of temperature on the main rheological properties (shear stress and plastic viscosity) as well as on the rheological behavior of water-based drilling muds (WBM). WBM_CMC and WBM_PAC (at Xn content fixed) were selected to evaluate the temperature effect (20°C; 40°C; 60°C and 80°C) on the rheological parameters and the rheological behavior. The results revealed that the shear stress and the plastic viscosity of the studied muds were considerably affected by an increase in temperature. A significant decrease in these drilling mud parameters as a function of temperature up to 80°C. A reduction of 58.8% in shear stress and 78.5% in plastic viscosity was observed. The results show that regardless of the test temperature, the shear thinning behavior of the WBM_CMC and WBM_PAC drilling muds is the same as the Herschel-Bulkley model.

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Wykorzystanie odpadów wydobywczych modyfikowanych wapnem do budowy wałów przeciwpowodziowych

Pilecka Elżbieta, Morman-Wątor Justyna

Materiały Budowlane

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2022

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nr 7

33--37

PL

W artykule przedstawiono wyniki badań właściwości fizycznych i mechanicznych odpadów wydobywczych o uziarnieniu mniejszym od 2 mm, zmodyfikowanych spoiwem wapiennym, w aspekcie wykorzystania ich jako materiału budowlanego do budowy wałów przeciwpowodziowych. Wyniki badań laboratoryjnych wskazują na poprawianie właściwości fizycznych, a przede wszystkim zmniejszenie współczynnika filtracji o 98%. Analiza wyników obliczeń MES modelu wału przeciwpowodziowego w programie MIDAS wykazała zwiększenie współczynnika stateczności do bezpiecznego poziomu.

EN

This article presents the results of tests of the physical and mechanical properties of mining waste with a grain size less than 2 mm and modified with lime binder in the context of its use as a building material for the construction of flood embankments. The results of the laboratory tests indicate the improvement of the physical properties, particularly the reduction of the filtration coefficient by 98%. The analysis of the results of FEM in the MIDAS program of the flood embankment showed an increase in the stability coefficient to a safe level.

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Non-prismatic channels for reducing shear stress

Haddad Samir

Journal of Water and Land Development

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2022

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no. 52

87--94

EN

To reduce the sediment transport capacity, shear stress needs to be reduced as well. The article describes work that has been done to find a way to make these reductions possible. The theoretical study and the approach proposed allowed us to obtain a general equation that determines conditions and calculates the most important parameters which support the reduction of shear stress. This describes the mechanism that erodes soils by free surface water flow. In a similar vein, we have shown that adding a short non-prismatic channel to the entrance of a prismatic channel, which has the same geometric shape, is a very powerful way to reduce shear stress. With the idea of reducing shear stress, we have shown that the water-surface profile type plays a key role and must therefore be included in future reflections on reducing the importance of shear stress. Additionally, the notion of efficiency was introduced that allows to evaluate the expected gain after the reduction of shear stress and adding a short non-prismatic channel. The laws of similarity applied to free surface flows allowed us to obtain an equation with several equivalence scales and compare different geometric shapes in terms of their efficiency in the reduction of shear stress.

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The assessment of an acoustic Doppler velocimetry profiler from a user’s perspective

Liu Da, Alobaidi Khaldoon, Valyrakis Manousos

Acta Geophysica

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2022

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Vol. 70, no 5

2297--2310

EN

Acoustic Doppler velocimetry profilers (ADVPs) are widely used in both experimental and field studies because of their robustness in velocity measurements. The acquired measurements do not only offer estimates of the local and instantaneous flow velocity at the interrogated measurement volume, but can also be further processed for the estimation of the bed surface shear stresses, thus they are finding a wide range of applications ranging from water engineering to geomorphology and ecohydraulics. This study aims to evaluate the performance of an ADVP in obtaining hydrodynamics measurements under fixed flow conditions, with various probe configurations. To this goal, a robust search is conducted where ADVP probe settings are sequentially altered. A number of assessment criteria are used including qualitative observations, such as checking the shape of the velocity profile, as well as quantitative error metrics, including signal-to-noise ratio, correlations and number of spikes. Further, estimation of the bed shear stresses computed by means of using the log Law of the Wall and turbulent kinetic energy, allow obtaining a better understanding of the uncertainties involved and the importance of making a better informed choice with respect to the probe configuration settings. Thus, the methodology and performance metrics provided herein, although presented for a given flow, can generally be applied from practitioners and researchers alike.

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Wpływ zbrojenia spoin wspornych ścian ścinanych z otworami, wykonanych z silikatowych elementów murowych, na zależności naprężenie ścinające – kąt odkształcenia postaciowego oraz naprężenia rysujące i niszczące

Jasiński Radosław

Materiały Budowlane

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2021

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nr 12

3--5

PL

W artykule przedstawiono wyniki badań ścian zbrojonych z otworami o rożnym kształcie wykonanych z silikatowych elementów murowych. Określono wpływ zbrojenia na zależność naprężenie ścinające – kąt odkształcenia postaciowego oraz wartość naprężeń rysujących i niszczących. Wykonano i zbadano 12 ścian o zewnętrznych wymiarach l = 4,45 m, h = 2,45 m, t = 180 mm z otworami zróżnicowanymi pod względem kształtu i wymiarów. W przypadku wszystkich zbrojonych modeli stopień zbrojenia elementów wynosił ρ = 0,07 (> ρmin = 0,05). Ściany badano przy wstępnych naprężeniach ściskających σc = 0,1; 1,5 lub 0,75 N/mm2. Wykazano istotny wpływ zbrojenia na sztywność ścian oraz wartość analizowanych naprężeń w chwili zarysowania i zniszczenia.

EN

The article presents the results of research on reinforced walls with openings of various shapes made of calcium-silicate masonry units. The main aim of the conducted experiments was to determine the influence of the applied reinforcement, on the relationship shear stress – shear strain angle and the value of cracking and ultimate stresses. 12 walls with external dimensions of l = 4,45 m, h = 2,45 m, t = 180 mm with openings of different shape and dimensions were constructed and tested. In all reinforced models, the element reinforcement ratio was ρ = 0,07 (> ρmin = 0,05). The walls were tested at the initial compressive stress of σc = 0,1; 1,5 or 0,75 N/mm2. The significant influence of the reinforcement on the wall stiffness and the values of the analyzed stresses at cracking and ultimate was demonstrated.

9

Modeling the hydrodynamic interactions between the river morphology and navigation channel operations

Neveen Badawy Abdel-Mageed, El-Hazek Alaa N., Elsersawy Hossam Mohamed, Mohammed Ebtesam Rezk

Journal of Water and Land Development

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2021

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no. 51

1--10

EN

The Nile River is the main route for inland navigation in Egypt. The vessels navigating through inland waterways generate complex physical forces that need to be studied extensively. Quantifying the effects of vessels sailing along a waterway is a complex problem because the river flow is unsteady and the river bathymetry is irregular. This paper aims to investigate the hydrodynamic effects resulting from the movement of vessels such as return currents around the vessel, the draw down of the water surface, under keel clearance, and the shear stress induced by vessels operating in the Nile River. Modeling such effects has been performed by applied the two-dimensional ADH (adaptive hydraulics) model to a river reach for different navigation channel operation scenarios. The obtained results show that the draw down heights, the water fluctuation, and the shear stress magnitude are larger when the river cross sectionals are narrow and the shallow water depths. These river sections are considered more disposed to bed erosion and it is morphologically unsafe. The section having the narrowest width and the lowest depth was associated with the largest drawdown percentages of 98.3% and 87.3% in one-way and two-way scenarios. While the section having the widest width and the largest depth was associated with the least drawdown percentages of 48.5% and 51.9% in one-way and two-way scenarios. The section having the narrowest width and the lowest depth was associated with the largest fluctuations of 22.0 cm and 41.9 cm in one-way and two-way scenarios. While the section having the widest width and the largest depth was associated with the least fluctuations of 0.6 cm and 1.8 cm in one-way and two-way scenarios. The section having the narrowest width and the lowest depth was the worst section for under keel clearance of 5.0 cm and 33.3 cm in one-way and two-way scenarios. While the section having the widest width and the largest depth was the best section, where its clearance values were 183.2 cm and 155.0 cm in one-way and two-way scenarios. It is concluded that a numerical model is a valuable tool for predicting and quantifying the hydrodynamic effects of vessels moving through a two-dimensional flow field and can be used to evaluate different scenarios that are difficult to measure in the field or a physical model. Also, it provides visualization products that help us understand the complicated forces produced by vessels moving in a navigation channel.

10

Effects of stenosis and dilatation on flow of blood mixed with suspended nanoparticles: a study using homotopy technique

Sudha T., Umadevi C., Dhange M., Manna S., Misra J. C.

International Journal of Applied Mechanics and Engineering

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2021

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Vol. 26, no. 1

251--265

EN

The paper deals with a theoretical study on blood flow in a stenosed segment of an artery, when blood is mixed with nano-particles. Blood is treated here as a couple stress fluid. Stenosis is known to impede blood flow and to be the cause of different cardiac diseases. Since the arterial wall is weakened due to arterial stenosis, it may lead to dilatation /aneurysm. The homotopy perturbation technique is employed to determine the solution to the problem for the case of mild stenosis. Analytical expressions for velocity, shear stress at the wall, pressure drop, and flow resistance are derived. The impact of different physical constants on the wall shear stress and impedance of the fluid is examined by numerical simulation. Streamline patterns of the nanofluid are investigated for different situations.

11

Shear Flow of Guncotton Pulp

Banishevsky Victor, Zakusylo Roman, Zakusylo Daryna

Central European Journal of Energetic Materials

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2021

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Vol. 18, no. 1

124--142

EN

This article considers aspects of the flow, rheology, and viscometry of guncotton pulp. It is substantiated that during production guncotton pulp is subjected to shear deformation, taking into account sliding over smooth surfaces, in the input zones of the dies, in the barrel, and on the crimped finned tube of the screw extruder. At the same time, the presence of shear stress in guncotton pulp has not been established. A rotational viscometer with a torque meter, which was developed during this research, enabled the presence of shear stress in guncotton pulp to be demonstrated. The values of the flow stress depend on the solvent content in the guncotton pulp; as this is decreased, the τ0 value increases. When the flow curve for the section from τ0 to τRmax was constructed, the flow curves of the guncotton pulp were described by the Herschel-Bulkley equation. The flow curves of guncotton pulp obtained on corrugated capillaries of different sizes are non-invariant and depend on the magnitude of the deformation of the guncotton pulp in the capillaries. Guncotton pulp flows in a narrow range of pressures and deformations.

12

Theoretical and experimental analysis on the interaction properties between tracks and sediments considering sand content for unmanned underwater tracked bulldozer

Li Yong, He Dingchang, Si Qiaorui

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2021

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Vol. 69, nr 1

art. no. e136036

EN

The unmanned underwater tracked bulldozer (UUTB) is an indispensable equipment for dredging and cleaning obstacles on the river bed in the flood season. The investigation on the interaction properties between the UUTB tracks and sediments provides foundation for the evaluation of operation performance when it works on the inland river bed. Based on the current worldwide research, the sediments mixed by sand, bentonite and water with sand content 0%, 10% and 20% were configured in this study to replace the real sediments on the inland river bed in China. The current pressure-sinkage model and shear stress-shear displacement model were discussed. Three different tracks were tested for the pressure-sinkage and the shear stress-shear displacement on the platform. The relationship between pressure and sinkage under sand content 0%, 10% and 20% are revealed based on the experimental results. The modulus of cohesive deformation and friction deformation of the sediments under said sand content are presented. The curves of shear stress and shear displacement are also obtained, which demonstrates the properties between the tracks and configured sediments under sand content 0%, 10% and 20%. The relationship between the tractive force and slip ratio with three different tracks under said sand content is also presented based on the quantitative analysis, which provides reference for the dynamics control and performance evaluation of UUTB on the inland river bed.

13

Shear stresses of hollow lightweight concrete beams made with wood waste

Alharishawi Salam Salman Chiad, Rajaa Nagham, Shihab Lina Abdulsalam

Archives of Civil Engineering

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2021

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Vol. 67, nr 1

657--672

EN

Hollow Lightweight Concrete (HLC) beams are gaining popularity due to low cost and low weight as compared with the Solid Lightweight Concrete (SLC) beams. HLC and SLC beams decrease in weight, without losing strength and durability. Flexural and shear behavior of reinforced HLC and SLC beams made with sawdust under two-point load is investigated in this study. The ultimate deformation efficiency and shear resistant mechanism of HLC beams are discussed experimentally and compared with other SLC beams. The beams, tested in this research, are rectangular. Beams were designed and constructed as 12 * 23 * 100 cm. Six concrete beam models were prepared including three SLC beams without the hollow and the other three HLC beams poured hollow 50 * 7.5 cm throughout the all beam of 100 cm. All beams were split according to the distance between vertical stirrups, these stirrups were divided into three specimens 45, 13, and 6 cm. By analyzing six experimental test beams, in this research, investigated the effect of diverse factors on the shear of beams. On comparison with normal concrete beams, this work describes the failure of mechanism, process, and ductility. The first crack loads, ultimate loads, load-deflection behavior, crack patterns and shapes of failure were investigated in this study. The experimental results show the ultimate performance of HLC beams are pure shear and controlled by yielding tension and compression steel bars. Also, it is found that the measured size and configuration of the hollow opening had an effect on the load-carry capacity and mid-span deflection of HLC beams. Thus, the design and construction details of beams can be additionally customized to reduce the total cost and weight of the HLC beams.

14

Effective parameters of tail processing gold-bearing ore hydrotransport for verninskaya processing factory

Alexandrov Victor I., Maharatkin Pavel N., Trufanova Inna S.

Zeszyty Naukowe. Organizacja i Zarządzanie / Politechnika Śląska

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2020

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z. 145

9--21

EN

Purpose: The paper shows that in order to increase the efficiency of hydraulic transport systems in mining a transition to the transportation of slurries with a high concentration of solids in the slurry flow is necessary. Design/methodology/approach: The aim of the research is to determine the optimal concentrations to ensure effectiveness of thickened tailings hydrotransport using the example of the Verninskaya processing factory, taking into account the maximum possible concentration of the solid phase and the rheological properties of the pulp. Findings: Experimental studies have shown that slurry tailings of gold-containing ore with mass concentrations of more than 55% are viscoplastic fluids. Experiments on a rotational viscometer allowed us to establish the main rheological characteristics of the studied slurries — shear stress and the dynamic effective viscosity. It has been established that over the entire range of concentrations from 55 to 65%, the flow of slurries is described by the Bingham rheological equation. Experimental studies of hydraulic transport performed on a laboratory setup with a pipeline diameter of 50 mm confirmed the results obtained on a rotational viscometer. Curves of mixture stream are inclined straight lines that cut off on the axis of head of the sections, which determine the initial hydraulic slope corresponding to the yield shear stress on the rheological curves. Originality/value: According to the results of the experiments, a method has been developed for calculating the hydraulic transport of high concentrated slurries of tailings of gold-bearing ore. Calculations showed that in a given range of performance of hydrotransport system and the mass concentration of the solid phase pressure losses vary from 11 to 84 m water column/m. Head loss values grow with increasing concentration. A sharp increase in head loss occurs in the concentration range from 60 to 65% and above.

15

A shear deformation theory of beams with bisymmetrical Cross-sections based on the Zhuravsky shear stress formula

Magnucki Krzysztof, Lewinski Jerzy, Magnucka-Blandzi Ewa

Engineering Transactions

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2020

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Vol. 68, iss. 4

353--370

EN

This paper is devoted to simply supported beams with bisymmetrical cross-sections under a generalized load. Based on the Zhuravsky shear stress formula, the shear deformation theory of a planar beam cross-section is formulated. The deflections and the shear stresses of exemplary beams are determined. Moreover, the numerical-FEM computations of these beams are carried out. The results of the research are shown in figures and tables.

16

Tests of polymeric adhesive joints in aspect of their application in prefabricated timber structures

Śliwa-Wieczorek Klaudia, Zając Bogusław, Kozik Tomasz

Archives of Civil Engineering

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2020

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Vol. 66, nr 1

113--125

EN

The article concerns modern, flexible adhesive joints, which might be used in timber construction. The article discusses the test results carried out for timber elements joints using polymeric adhesives produced by Sika®. The scope of the tests includes the analysis of strength criteria, tests of polymer adhesion to the timber with a pull-off method, tests of polymer layer shearing between timber elements as well as examination of bending of timber elements joined with polymer. The conclusions indicate the types of these polymers which are recommended for the creation of polymeric joints of timber-polymeric type in timber constructions.

PL

Dynamiczny rozwój połączeń klejowych, umożliwia ich zastosowanie już nie tylko w naprawach, czy wzmocnieniach głównie konstrukcji żelbetowych oraz murowych. Coraz częściej mówi się o zastąpieniu tradycyjnych łączników przez połączenia klejowe. Szczególnie interesujący jest rozwój połączeń na bazie polimerów w zastosowaniu w konstrukcjach drewnianych, który umożliwia eliminację lub znaczne ograniczenie występowania zjawiska koncentracji naprężeń, jak ma to miejsce w przypadku najbardziej powszechnych połączeń trzpieniowych. Szczególne znaczenie ma eliminacja tego zjawiska w obiektach drewnianych, poddanych oddziaływaniu silnych wiatrów, trzęsień ziemi, czy też dużych gradientów temperaturowych oraz wilgotności. Głównym celem artykułu jest omówienie wyników badań przeprowadzonych dla połączeń elementów drewnianych przy wykorzystaniu podatnych klejów polimerowych produkcji Sika®. Zakres badań obejmuje analizę kryteriów wytrzymałościowych, badania przyczepności polimeru do drewna metodą pull-off (na odrywanie), badania ścinania warstwy polimeru pomiędzy elementami drewnianymi oraz badania zginania elementów drewnianych zespolonych polimerem.

17

Naprężenia styczne w zginanej belce dwuwarstwowej badania analityczne

Łagoda Karolina

Modelowanie Inżynierskie

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2019

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T. 40, nr 71

56--62

PL

Podczas zginania materiałów wartości naprężeń stycznych są tak niewielkie, że można je pominąć. Warto jednak zauważyć, że na przykład w przypadku laminatów kompozytowych naprężenia styczne są uwzględniane w znacznie większym stopniu niż w materiałach izotropowych. W związku z powyższym postanowiono lepiej poznać rozkład naprężeń stycznych występujących w materiałach. Z reguły stosuje się wzór Żurawskiego, który odzwierciedla rozkład naprężeń stycznych występujących w materiałach izotropowych. Jednak zastosowanie tego wzoru do materiałów warstwowych daje błędne rezultaty. W związku z tym, korzystając z metody elementów skończonych, postanowiono przeanalizować rozkład naprężeń stycznych w próbkach wykonanych z dwóch warstw z różnych materiałów.

EN

When bending materials, the values of shear stresses are so small that they can be omitted. It is worth noting, however, that for example in the case of composite laminates, shear stresses are taken into account in a much greater extent than in isotropic materials. In connection with the above, it was decided to learn better the distribution of shear stresses occurring in the materials. Usually, the shear stress in beams equation is used, which reflects the distribution of shear stresses occurring in isotropic materials. However, the use of this equation for layered materials gives erroneous results. In connection with the above, using the finite element method, the distribution of shear stresses in specimens made of two layers from different materials was analyzed.

18

Investigation of shear stress distribution in a 90 degree channel bend

Lee S. K., Dang T. A., Le V. T.

International Journal of Applied Mechanics and Engineering

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2019

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Vol. 24, no. 1

213--220

EN

Shear stress is a key parameter that plays an important role in sediment transport mechanisms; therefore, understanding shear stress distribution in rivers, and especially in river bends, is necessary to predict erosion, deposition mechanisms and lateral channel migration. The aim of this study is to analyze the shear stress distribution near a river bed at 90-degree channel bend using a depth-average method based on experimental measurement data. Bed shear stress distribution is calculated using the depth-averaged method based on velocity components data has been collected from a 3D-ADV device (three-dimensional acoustic doppler velocity) at different locations of a meandering channel. Laboratory experiments have been made at the hydraulic laboratory of the RCRFIDF (Research Center for River Flow Impingement and Debris Flow), Gangneung-Wonju National University, South Korea to provide data for simulating the incipient motion of the riverbed materials and then predicting the river morphological changes in the curved rivers. The calculated results show that the maximum value of shear stress distribution near the riverbed in the different cross sections of the surveyed channel occurs in a 70-degree cross section and occurs near the outer bank. From the beginning of a 40-degree curved channel section, the maximum value of the shear stress occurs near the outer bank at the end of the channel.

19

Assessment of shear stresses from shrinkage and thermal deformation in wood-concrete bridge beams

Furtak K.

Archives of Civil Engineering

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2019

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Vol. 65, nr 4

37--50

EN

The aim of the paper is to assess the values of shear (delaminating) stress in the composition plane between the concrete (RC) deck slab and wood girder from concrete shrinkage, and shrinkage and swelling of wood, as well as difference in temperature between the wood web and concrete slab.

20

Numerical and experimental research on delamination of glulam elements

Kawecki B., Podgórski J.

Archives of Civil Engineering

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2018

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Vol. 64, nr 3

15--29

EN

The paper presents numerical and experimental research on glulam delamination in a double lap connection with predominant shear stresses. Laboratory tests and wide literature survey enabled to determine timber and glue joint parameters. Cohesive zone theory, generally used for epoxy matrix and fiber reinforced composites, was adopted to modelling glue layer delamination in glulam elements. Numerical models were validated with laboratory tests.

PL

W artykule podjęto temat komputerowego modelowania połączenia dwu-zakładkowego w drewnie klejonym. Dokonano dwuetapowej kalibracji modelu numerycznego na podstawie badań laboratoryjnych. Próbki wykonano poprzez pocięcie belek z drewna klejonego, pomijając większe sęki lub połączenia lameli w celu uzyskania możliwie jednorodnego materiału. Zarówno w przypadku badań laboratoryjnych jak i w analizach numerycznych sterowano przyrostem przemieszczenia mierząc wartość siły pionowej.