Wyniki wyszukiwania - BazTech

1

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

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.

3

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.

4

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.

5

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.

6

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.

7

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.

8

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.

9

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.

10

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.

11

Beam bond tests of GFRP and steel reinforcement to concrete

Szczech D., Kotynia R.

Archives of Civil Engineering

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2018

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Vol. 64, nr 4/II

243--256

EN

The paper presents research program of bond between glass fiber reinforced polymer bars and concrete in reference to the steel bars. Bond between the reinforcement and concrete is a crucial parameter governing a behaviour of reinforced concrete members and transferring of the internal forces from concrete to the reinforcement. The use of FRP bars as an equivalent reinforcement to steel in concrete structures has increased in recent years. The FRP bars are very different from steel, mainly due to much lower elasticity modulus and their anisotropic structure. Good performance of FRP reinforced concrete requires sufficient interfacial bond between bars and concrete. However, there are no specific standards referring to the surface preparation of these bars, that leads to variable bond behaviour of the composite reinforcement to the concrete. The objective of the study was to investigate the influence of variable parameters on the bond behaviour to concrete. The experimental program consisted of eighteen beam bond specimens varying in: bar diameter (12mm, 16mm, 18mm) and type of reinforcement (GFRP sand – coated and steel bars). Although the GFRP bars indicated good bond behaviour to concrete, the average bond strength was slightly lower than that of steel reinforcement of 16mm and 18 mm, while it was higher for the GFRP bars of 12mm diameter.

12

Wpływ montmorylonitu na wartość granicy płynięcia smaru plastycznego wytworzonego na bazie roślinnej

Kozdrach R.

Nafta-Gaz

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2017

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R. 73, nr 9

698--706

PL

W publikacji przedstawiono wyniki badań wpływu różnej ilości dodatku modyfikującego na wartość granicy płynięcia smaru plastycznego. Do modyfikacji smaru plastycznego wytworzonego na bazie roślinnej i zagęszczonego stearynianem litu zastosowano montmorylonit jako przedstawiciela krzemianów warstwowych. Badania doświadczalne wartości granicy płynięcia wykonano przy użyciu reometru rotacyjnego Physica MCR 101 (prod. Anton Paar), zawierającego dyfuzyjne łożysko powietrzne, podłączone do zasilania pneumatycznego – bezolejowego kompresora Jun-Air oraz bloku osuszającego powietrze. Aparat wyposażony jest w układ Peltiera kontroli temperatury w zakresie –40÷200°C oraz w zewnętrzny układ termostatujący VISCOTHERM V2, pracujący w zakresie temperatur –20÷200°C. Sterowanie reometrem oraz analizę danych pomiarowych przeprowadzono za pomocą oprogramowania Rheoplus. Badania wykonywano, stosując układ pomiarowy stożek–płytka, w zakresie szybkości ścinania 0,01÷100 s-1 w temperaturze 20°C dla smaru bazowego, tzn. niezawierającego dodatku modyfikującego, i porównano je z wynikami uzyskanymi dla smarów plastycznych zmodyfikowanych różnymi ilościami montmorylonitu. Do oceny wartości granicy płynięcia wykorzystano wyniki badań zależności naprężenia ścinającego od szybkości ścinania (tzw. krzywe płynięcia). Do teoretycznego wyznaczenia granicy płynięcia zastosowano następujące modele reologiczne: Binghama, Herschela-Bulkleya oraz Cassona. Przeprowadzone badania wykazały, że dodatek do 3% montmorylonitu wpływa na wzrost wartości granicy płynięcia badanych smarów plastycznych. Dalsze zwiększanie zawartości dodatku w smarze przyczynia się do obniżenia granicy płynięcia, co powoduje zmniejszenie oporów przepływu powstałych kompozycji smarowych w układzie smarowniczym.

EN

The paper presents the results of studies on the effect of different amounts of modifying additiveson the value of yield point of lubricating grease. For the modification of lubricating grease produced on vegetable base oil and thickened with lithium stearate, montmorillonite as a representative of stratified silicate was used. The yield point experimental research was carried out using a rotational rheometer Physica MCR 101 (prod. Anton Paar), equipped with a diffusion air bearing, connected to the air supply – an oil-free compressor Jun-Air and block draining the air. The apparatus was equipped with a Peltier system for temperature control in the range of –40÷200°C and an outside thermostatic system VISCOTHERM V2, working in the range of –20÷200°C. Rheometer control and measurement data analysis were performed using the Rheoplus software. The measurements were carried out using a cone-plate measuring system, with a shear rate range of 0.01÷100 s-1 at the temperature of 20°C for lubricating grease, which didn’t contain a modifier and were compared with the results obtained for lubricating greases modified with different amounts of montmorillonite. The results of the shear stress dependence test on the shear rate (so called flow curves) were used to evaluate the yield point. For the theoretical determination of yield point the following rheological models: Bingham, Herschel-Bulkley and Casson were used. Studies have shown that the addition of up to 3% of montmorillonite affects the increase of the yield point of the tested greases. Further increasing the additive content in the grease contributes to lowering the yield point, thus reducing the flow resistance of the resulting lubricant compositions in the lubrication system.

13

Wpływ metody rozdziału oddziaływań poziomych na wartości obciążenia tarcz ściennych budynku o drewnianej konstrukcji szkieletowej

Roszczyc R., Szkobodziński M.

Materiały Budowlane

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2017

|

nr 7

71--73

PL

W artykule omówiono problem wpływu doboru metody oceny oddziaływań poziomych na wartość obciążenia tarcz ściennych budynku o drewnianej konstrukcji szkieletowej. Ponadto przedstawiono przykład obliczeniowy budynku o niesymetrycznym układzie ścian usztywniających, w przypadku którego przeprowadzono rozdział obciążeń metodami analitycznymi oraz metodą numeryczną.

EN

This article presents the problem of distribution of lateral loads on the shear walls in a wood frame buildings. The paper presents methods of lateral load distribution and their comparison on the example of a building with an eccentric location of shear walls. The results obtained from the analytical methods were compared with the results obtained from numerical calculations made using the finite element method.

14

Wave-induced bedload transport – a study of the southern Baltic coastal zone

Dudkowska A., Gic-Grusza G.

Geologos

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2017

|

Vol. 23, No. 1

1--14

EN

The wave-induced bedload transport and spatial distribution of its magnitude in the southern Baltic coastal zone of Poland are estimated. The vicinity of Lubiatowo was selected as a representative part of the Polish coast. It was assumed that transport is a function of shear stress; alternative approaches, based on force balances and discharge relationships, were not considered in the present study. Four models were studied and compared over a wide range of bottom shear stress and wind-wave conditions. The set of models comprises classic theories that assume a simplified influence of turbulence on sediment transport (e.g., advocated by authors such as Du Boys, Meyer-Peter and Müller, Ribberink, Engelund and Hansen). It is shown that these models allow to estimate transport comparable to measured values under similar environmental conditions. A united general model for bedload transport is proposed, and a set of maps of wave bedload transport for various wind conditions in the study area is presented.

15

O wpływie niemetalicznego zbrojenia głównego na mechanizm niszczenia i nośność ścinania betonowych belek bez zbrojenia poprzecznego

Kotynia R., Kaszubska M.

Czasopismo Inżynierii Lądowej, Środowiska i Architektury / Journal of Civil Engineering, Environment and Architecture

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2017

|

z. 64, nr 3/I

247--258

PL

W pracy przedstawiono wyniki doświadczalnych badań belek bez zbrojenia poprzecznego zbrojonych na zginanie prętami wykonanymi z włókien szklanych. Celem badań była analiza zachowania się belek pod obciążeniem wraz z określeniem wpływu intensywności tego zbrojenia na sposób niszczenia i nośność ścinania. Do analizy odkształcalności i rozwoju zarysowania elementów badawczych użyto systemu cyfrowej korelacji obrazu ARAMIS. Korzystając z kinetycznego modelu ścinania opisano proces niszczenia belek oraz określono położenie i nachylenie ukośnych rys niszczących. Badania wykazały, że niszczące naprężenia ścinające rosną wraz ze wzrostem stopnia zbrojenia głównego, przy czym wpływ liczby prętów i ich średnicy - w ramach grupy belek o jednakowym stopniu zbrojenia - na ogół nie był istotny, większe znacznie miała liczba warstw prętów, zwłaszcza przy najwyższym stopniu zbrojenia.

EN

The paper presents experimental test results of concrete beams with longitudinal GFRP reinforcement without transversal reinforcement. The aim of the test was analysis of the beams’ behavior under loading and influence of the flexural reinforcement on the failure mechanism and the shear capacity. For analysis of the beams’ deformability the digital image correlation system ARAMIS was used. Based on kinematic shear model the process of failure was described in details with location of the critical shear crack and its inclination. Test results indicated that the ultimate shear stress increases with increase in the flexural reinforcement ratio, while the shear stress is not affected by a number of the bars and their diameter. Much more affected was a number of the reinforcement levels, especially in the beam with the highest longitudinal reinforcement ratio.

16

Wzmocnienie kompozytowe PBO-FRCM. Cz.2

Urbańska D., Musiał M.

Builder

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2017

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R.21, nr 9

64--66

PL

Kompozyty PBO-FRCM (Fibre Reinforced Cementitious Matrix) składają się z włókien PBO (p-Phenylene Benzobis Oxazole) i zaprawy mineralnej, która pełni rolę matrycy. Dzięki temu, w przeciwieństwie do kompozytów FRP, mogą być one stosowane w obiektach narażonych na oddziaływanie wysokiej temperatury. Zastosowanie zaprawy jako matrycy wiąże się jednak ze specyficzną mechaniką pracy tego systemu, która znacznie odróżnia go od systemów FRP. W badaniach przeprowadzonych na kompozytach PBO-FRCM wykazano, że w tym systemie dochodzi do poślizgu między włóknami a warstwą matrycy. Wiąże się z niedokładnym pokryciem wszystkich włókien zaprawą i występowaniem tzw. efektu teleskopowego. W artykule opisano mechanizm pracy wzmocnienia kompozytowego PBO-FRCM poddanego rozciąganiu oraz naprężeniom ścinającym. Omówiono trójfazowy mechanizm pracy kompozytów FRCM oraz główne problemy związane z zastosowaniem tego typu systemu, czyli przedwczesne odspajanie się włókien od matrycy.

EN

PBO-FRCM (Fibre Reinforced Cementitious Matrix) composites cosist of PBO fobers and mineral mortar used as a matrix. It can therefore be used in places exposed to high temperatures, contrary to the systems FRP. The use of mortar, however, is associated, however, with the specific mechanics of work of this system, which significantly differentiates it from FRP systems. The performed studies have shown that in the FRCM system slippage occurs between the fibers and the matrix layer, which is associated with inaccurate coverage of all fibers by mortar and the occurrence of "telescopic effect". The article describes the work mechanism of PBO-FRCM composites subjected to tensile and shear stresses. Three-phase work of FRCM composites and main problems associated with the use of this type of system, which is among other things premature debonding of the fibers from the matrix, were discussed.

17

Investigation of blood flow rheology using second-grade viscoelastic model (Phan-Thien–Tanner) within carotid artery

Ramiar A., Larimi M. M., Ranjbar A. A.

Acta of Bioengineering and Biomechanics

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2017

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Vol. 19, no. 3

27--41

EN

Purpose: Hemodynamic factors, such as Wall Shear Stress (WSS), play a substantial role in arterial diseases. In the larger arteries, such as the carotid artery, interaction between the vessel wall and blood flow affects the distribution of hemodynamic factors. The fluid is considered to be non-Newtonian, whose flow is governed by the equation of a second-grade viscoelastic fluid and the effects of viscoelastic on blood flow in carotid artery is investigated. Methods: Pulsatile flow studies were carried out in a 3D model of carotid artery. The governing equations were solved using finite volume C++ based on open source code, OpenFOAM. To describe blood flow, conservation of mass and momentum, a constitutive relation of simplified Phan-Thien–Tanner (sPTT), and appropriate relations were used to explain shear thinning behavior. Results: The first recirculation was observed at t = 0.2 s, in deceleration phase. In the acceleration phase from t = 0.3 s to t = 0.5 s, vortex and recirculation sizes in bulb regions in both ECA and ICA gradually increased. As is observed in the line graphs based on extracted data from ICA, at t = 0.2 s, τyy is the maximum amount of wall shear stress and τxy the minimum one. The maximum shear stress occurred in the inner side of the main branch (inner side of ICA and ECA) because the velocity of blood flow in the inner side of the bulb region was maximum due to the created recirculation zone in the opposite side in this area. Conclusions: The rheology of blood flow and shear stress in various important parts (the area that are in higher rates of WSS such as bifurcation region and the regions after bulb areas in both branches, Line1–4 in Fig. 7) were also analyzed. The investigation of velocity stream line, velocity profile and shear stress in various sections of carotid artery showed that the maximum shear stress occurred in acceleration phase and in the bifurcation region between ECA and ICA which is due to velocity gradients and changes in thinning behavior of blood and increasing strain rate in Newtonian stress part.

18

Zastosowanie systemu Aramis do trójwymiarowego pomiaru lokalnych odkształceń kompozytów

Oliwa R.

Mechanik

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2015

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R. 88, nr 12CD2

147--151

PL

W pracy przedstawiono możliwości wykorzystania tzw. metod badań nieniszczących do charakterystyki kompozytów polimerowych. W tym celu zastosowano system Aramis umożliwiający trójwymiarowy pomiar odkształceń na powierzchni próbki w trakcie oznaczania naprężenia ścinającego laminatów podczas rozciągania pod kątem 45° w stosunku do ułożenia włókien.

EN

The study presents the possibilities of using the nondestructive testing methods (NDT) to characterize the polymeric composites. For this purpose the Aramis system is useful tool allows to measure the three-dimensional strain on the sample surface during the tensile test at 45° relative to the fibers.

19

Evaluation of the influence of shrinkage strain on the fatigue strength of the connection in steel–concrete composite beams

Furtak K.

Archives of Civil and Mechanical Engineering

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2015

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Vol. 15, no. 3

767--774

EN

The paper presents the author's proposal for calculation of shear stresses (disintegrating) induced by concrete shrinkage at the interface of steel and concrete. The proposal also presents expressions to calculate the fatigue strength of a connection in steel–concrete composite girders. The expressions to calculate fatigue strength are based on the results of experiments performed by the author. Based on the results of analyses it can be stated that the load bearing capacity of a connection with flexible shear connectors is strongly affected by a concrete slab adhesion to a steel girder. This effect depends on the stiffness ratio of the girder to concrete deck (coefficient δ), concrete strength and diameter of shear studs d, as well as the value of shrinkage strain of concrete. Fatigue strength of a connection with strip connectors is affected by the geometry of the composite girder and its components, concrete strength and concrete shrinkage strain. At low values of δ, low concrete grades and large diameters of shear connectors or holes, the fatigue strength of the composite connection is likely to be exhausted.

20

Estimation of Apollo Lunar Dust Transport using Optical Extinction Measurements

Lane J. E., Metzgert P. T.

Acta Geophysica

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2015

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Vol. 63, no. 2

568--599

EN

A technique to estimate mass erosion rate of surface soil during landing of the Apollo Lunar Module (LM) and total mass ejected due to the rocket plume interaction is proposed and tested. The erosion rate is proportional to the product of the second moment of the lofted particle size distribution N(D), and third moment of the normalized soil size distribution S(D), divided by the integral of S(D)⋅D2/v(D), where D is particle diameter and v(D) is the vertical component of particle velocity. The second moment of N(D) is estimated by optical extinction analysis of the Apollo cockpit video. Because of the similarity between mass erosion rate of soil as measured by optical extinction and rainfall rate as measured by radar reflectivity, traditional NWS radar/rainfall correlation methodology can be applied to the lunar soil case where various S(D) models are assumed corresponding to specific lunar sites.