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1

Thermal characterization of halloysite materials for porous ceramic preforms

Kujawa M., Suwak R., Dobrzański L.A., Gerle A., Tomiczek B.

Archives of Materials Science and Engineering

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2021

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Vol. 107, nr 1

5--15

EN

Purpose: The aim of the study was to investigate the possibility of sintering raw (natural) halloysite and pure halloysite to produce porous ceramic preforms, and determination of sintering temperature based on the results of investigations into thermal effects, linear changes and phase transitions. Design/methodology/approach: Due to mullitisation ability of halloysite at high temperature, alternative applications based on the sintering technology (including the production of reinforcement of metal matrix composites) are being searched for. Pure halloysite and Dunino halloysite were selected for the study. Findings: Pure halloysite, characterized by low impurities, dimensional stability during sintering, softening temperature above 1500ºC and ability to transform into mullite at temperatures above 950ºC could be used as a base for the production of sintered, porous mullite preforms. Research limitations/implications: Presence of impurities in Dunino halloysite, contribute to the shift of the sintering temperature towards lower temperatures and caused a rapid and uncontrolled shrinkage of the sample and the appearance of the softening temperature at 1300ºC. Practical implications: Based on the research of thermal (DTA/TG, linear changes in high-temperature microscopy) and XRD studies it is possible to determine the sintering temperature of pure halloysite to manufacture the porous mullite preforms with open porosity. Originality/value: The received results show the possibility of obtaining the new mullite preforms based on pure halloysite.

2

The Influence of Uniaxial Compression on the Friction Coefficient (Polymer–Steel Pair), Wear, and Hardness in Selected Thermoplastics

Kujawa M.

Tribologia

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2018

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nr 3

77--82

EN

Plastic plain bearings are deformed during assembly. According to one of the leading manufacturers of plastic sliding elements, the bushing’s internal diameter may be reduced by up to 2.5%. Moreover, plastic sliding elements are increasingly used in harsh conditions (e.g., under high pressure). However, there are no papers that describe the influence of deformation under compression on the tribological properties of plastics. Specimens made of PTFE, PA6, and PE-HD were deformed while conducting the current research, and this deformation was maintained during cooperation with steel. The results of microhardness, wear, and the coefficient of friction tests were compared to data gathered during tests of non-deformed specimens. During deformation under compression (e ≈ 6%), microhardness lowered by up to 30% (PTFE). A significant reduction of hardness (by up to 15%) was observed when strain was only 2%, and up to this value of strain, there is mainly elastic deformation in the polymer. Changes of the coefficient of friction values were insignificant. In terms of PTFE and PE-HD, during deformation under compression up to e ≈ 6% , the block scar volumes were 20% and 40% larger, respectively, than the non-deformed form of specimens. In terms of PA6, the change in block scar volume was insignificant. It may seem that tension and compression ought to cause totally different effects. However, the comparison of the current results and the results described in the previous paper exposes that these two different processes led to the same effects – reducing hardness and increasing wear. Deformation of plastic sliding components as an effect of assembly appears to be minor; however, it affects polymer microhardness and wear resistance.

PL

Polimerowe elementy ślizgowe podczas montażu w urządzeniu ulegają odkształceniu. Jeden z czołowych producentów elementów ślizgowych z tworzyw sztucznych podaje, że po montażu średnica wewnętrzna tulei może zmniejszyć się aż do 2,5%. Ponadto tego typu elementy są stosowane w coraz bardziej wymagającym otoczeniu (np. przy znacznym ciśnieniu), a w literaturze nie można znaleźć informacji na temat wpływu ściskania na właściwości tribologiczne. W opisanych badaniach utrzymywano w ściśnięciu próbki wykonane z PTFE, PA6 i PE-HD i w takim stanie poddano je współpracy ze stalą. Wyniki dotyczące współczynnika tarcia, zużywania i mikrotwardości porównywano z wartościami uzyskanymi dla nieodkształconych materiałów. Po ściśnięciu materiałów do e ≈ 6% mikrotwardość zmniejszyła się nawet o 30% (w przypadku PTFE). Znaczące zmiany mikrotwardości (do 15% różnicy) pojawiły się już przy odkształceniu do 2%, czyli w zakresie, gdzie dominują w polimerze odkształcenia odwracalne (sprężyste). Nie zaobserwowano znaczących zmian współczynnika tarcia. Dla PTFE i PE-HD po odkształceniu do e ≈ 6% objętość usuwanego podczas współpracy materiału zwiększyła się odpowiednio o 20% i 40%. W przypadku PA6 nie odnotowano znaczących zmian. Wydawać by się mogło, że ściskanie i rozciąganie powinny powodować przeciwstawne skutki. Porównując jednak uzyskane wyniki do tych z poprzednich badań, okazuje się, że prowadzą one do tego samego – zmniejszenia twardości i zwiększenia zużywania. Pomimo że odkształcenia wprowadzane do polimeru podczas montażu tudzież pracy elementu ślizgowego wydają się niewielkie, to mają one wpływ na twardość materiału i odporność na zużywanie.

3

Wpływ zmian klimatu na funkcjonowanie transportu kolejowego

Motowidlak U., Kujawa M.

Logistyka

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2018

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nr 5

13--17

PL

Większości elementów transportu kolejowego narażonych jest na bezpośrednie oddziaływanie czynników klimatycznych. Zwłaszcza infrastruktura narażona jest na bezpośredni kontakt czynników atmosferycznych, które mogą powodować zakłócenia w jej funkcjonowaniu. Do wdrożenia efektywnych działań adaptacyjnych i zapobiegawczych niezbędna jest ocena wrażliwości infrastruktury transportowej na czynniki klimatyczne, będąca efektem analizy danych klimatycznych i pogodowych oraz ich wpływu na stan infrastruktury, co stanowiło przedmiot rozważań podjętych w artykule.

EN

Most elements of rail transport are exposed to direct exposure to climatic factors. Infrastructure in particular is exposed to direct contact with atmospheric factors that can cause disruption to its functioning. In order to implement effective adaptation and prevention measures, it is necessary to assess the sensitivity of transport infrastructure to climatic factors, resulting from the analysis of climatic and weather data and their impact on the condition of infrastructure, which was the subject of considerations undertaken in the article.

4

The influence of a constant state of deformation on the friction coefficient in selected thermoplastics (polymer–steel pair)

Kujawa M., Wieleba W.

Tribologia

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2017

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nr 4

39--45

EN

The effect of tensile deformation on polymer structures and their mechanical properties is described in various papers. However, the majority of articles are focused on high deformation (a few hundred percentiles) at increased temperature. It causes changes in orientation and the crystallinity ratio. The authors of this paper asses the influence of strain (max. 50%) on hardness and the coefficient of friction (polymer–steel A1 couple) for selected polymers. The deformation was conducted at room temperature and maintained during tests. There was a significant reduction (up to 50%) of hardness after deformation, in the case of all examined polymers. In the case of PE-HD, the coefficient of kinetic friction almost doubled its value (89% increase). The reduction of the coefficient of static friction for sliding pairs that include PTFE and PA6 was about 26% (in comparison with non-deformed polymer). For all investigated polymers, hardness increased over time (up to 40% after 24 hours). Coefficients of static and kinetic friction decreased in 24 hours (up to 29% coefficient of static friction and 19% coefficient of kinetic friction). The research shows that a small deformation causes changes in polymer properties. Moreover, these changes appear at room temperature directly after deformation.

PL

Wpływ rozciągania na strukturę polimeru i jego właściwości jest szeroko opisany w literaturze. Jednakże publikacje dotyczące tej tematyki skupiają się na znacznych odkształceniach (kilkaset %) przy podwyższonej temperaturze. Zabieg ten powoduje orientację struktury i zmianę stopnia krystaliczności. Autorzy tej publikacji przebadali wpływ odkształcenia (max. 50%) na twardość i współczynnik tarcia po stali (A1). Próbki były rozciągane w temperaturze pokojowej, a odkształcenie utrzymywano podczas badań. W przypadku wszystkich badanych polimerów zaobserwowano znaczące zmniejszenie twardości po odkształceniu (aż do 50%). Dla pary PE-HD – stal (A1) po odkształceniu polimeru współczynnik tarcia kinetycznego niemalże podwoił swoją wartość (zwiększenie o 89%). Zmniejszenie współczynnika tarcia wynosiło do 26% dla par zawierających PTFE i PA6. Wraz z upływem czasu zwiększała się twardość polimerów (o maksymalnie 40% po 24 godzinach). Wartości współczynników tarcia statycznego i kinetycznego zmniejszyły się maksymalnie o odpowiednio 29% i19%. Badania ukazują, że nawet stosunkowo niewielkie odkształcenie powoduje zmiany właściwości polimeru. Ponadto modyfikacje pojawiają się bezpośrednio po odkształceniu w temperaturze pokojowej.

5

The influence of deformation of selected thermoplastics on the friction with steel

Kujawa M, Niemiec A., Wieleba W.

Tribologia

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2016

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nr 4

137--143

EN

Friction and wear of materials with additional deformation or stress is not a broadly described case. However, scientific publications considering this issue point out that additional deformation and stress ought to be taken into account during wear and friction analysis. In this article, the influence of strain in thermoplastics (POM, PTFE, PE-HD, PMMA) over the friction coefficient is described. Materials were deformed under tensile stress and examined after 24 hours. For specimens in which plastic strain was maintained, the decline of hardness (PE-HD: approximately 70% decrease, PTFE: approximately 40% decrease) and the reduction of the coefficient of kinetic friction (both PTFE and PE-HD: about 20% decrease) were observed. POM returned to its pre-deformed shape and PMMA was deformed without reaching its elastic limit. In these cases, only small changes in hardness (POM; approximately 10% decrease, PMMA: approximately 6% increase) and friction coefficients (maximum 4% change) occurred.

PL

Tarcie i zużycie materiałów odkształconych lub naprężonych w wyniku działania sił niepochodzqcych od współpracy w skojarzeniu nie jest obszernie opisanym zagadnieniem. Jednakże publikacje traktujące o tej tematyce są zgodne w jednym: stan odkształcenia i naprężenia w materiale powinien być brany pod uwagę przy analizie zjawiska tarcia i zużycia. W artykule opisano wpływ odkształcenia polimerów termoplastycznych POM, PTFE, PE-HD i PMMA na współczynnik tarcia polimer-stal. Materiały rozciągnięto i pozostawiono w stanie nienaprężonym na 24 godziny. W próbkach, w których wystąpiło i utrzymało się trwałe odkształcenie plastyczne zaobserwowano zmniejszenie twardości (dla PE-HD o okolo 70%, dla PTFE o okolo 40%) i redukcji współczynnika tarcia kinetycznego (dla obu polimerów o ponad 20%). POM, który całkowicie powrócił do pierwotnej postaci i PMMA rozciągnięty tylko w zakresie sprężystym wykazały niewielkie zmiany odnośnie do twardości (POM spadek o okolo 10% i PMMA wzrost o okolo 6%) i współczynnika tarcia (zmiana o maksymalnie 4%).

6

The effect of the ionizing radiation on the tribological properties of thermoplastic polymers rubbing against steel

Niemiec A., Kujawa M., Wieleba W.

Tribologia

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2016

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nr 5

133--145

EN

The paper describes the effects of gamma radiation doses on the tribological and mechanical properties of selected thermoplastic polymers: PEEK, PEI, PET, and PA6. Samples of those polymers were irradiated with gamma rays of energy 1, 1.2, 3, 4, 5 MeV and with the intensity of the radiation beam 4, 7, 10, 30, 40 μA. With an increasing dose of radiation, properties such as microhardness, the friction coefficient of polymers, and the wear rate are changed. The chemical structure of the irradiated polymer may be changed by crosslinking but also by chain scission. The modified polymers may be used in medical science, electronics, and space technology. In this article, we report the results of steel C45 – thermoplastics (PEEK, PEI, PET, and PA6) friction couple during the slip motion. The analysis is focused on the friction coefficient, wear rate, and microhardness. Kinematic parameters of the experiment in slide movement were constant and defined by the following values: contact pressure p = 1MPa and sliding velocity v = 1m/s. The authors observed that, as gamma radiation dose increased, the microhardness and friction coefficient increased and their wear intensity decreased. Polymers change their microstructure and molecular structure when they are subjected to gamma ray irradiation, which results in modification on many important physical and chemical properties.

PL

Celem niniejszej pracy było określenie wpływu dawki promieniowania gamma na właściwości tribologiczne i mechaniczne wybranych polimerów termoplastycznych: PEEK, PEI, PET, PA6. Wraz ze wzrostem dawki tego promieniowania właściwości takie jak microhardness, współczynnik tarcia statycznego oraz intensywność zużycia ulegają zmianie. Wymienione właściwości mogą być modyfikowane na skutek zachodzących zmian w strukturze chemicznej naświetlonych polimerów poprzez sieciowanie łańcuchów polimerowych, ale także ich rozerwanie. Zmodyfikowane polimery mogą być wykorzystane m.in. w medycynie, elektronice i technologii kosmicznej. W pracy opisano badania par ślizgowych stal C45 – wybrany polimer. Analizie poddano wartości współczynnika tarcia statycznego oraz intensywności zużycia materiału. Dla wszystkich analizowanych przypadków wartości parametrów ruchowych były stałe: siła nacisku wynosiła 1 MPa, a prędkość ślizgowa 1 m/s. Eksperyment wykazał zwiększenie wartości mikrotwardości i współczynnika tarcia oraz zmniejszenie intensywności zużycia.

7

Manufacturing of Porous Ceramic Preforms Based on Halloysite Nanotubes (Hnts)

Kujawa M., Dobrzański L. A., Matula G., Kremzer M., Tomiczek B.

Archives of Metallurgy and Materials

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2016

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Vol. 61, iss. 2B

917--922

EN

The aim of this study was to determine the influence of manufacturing conditions on the structure and properties of porous halloysite preforms, which during pressure infiltration were soaked with a liquid alloy to obtain a metal matrix composite reinforced by ceramic, and also to find innovative possibilities for the application of mineral nanotubes obtained from halloysite. The method of manufacturing porous ceramic preforms (based on halloysite nanotubes) as semi-finished products that are applicable to modern infiltrated metal matrix composites was shown. The ceramic preforms were manufactured by sintering of halloysite nanotubes (HNT), Natural Nano Company (USA), with the addition of pores and canals forming agent in the form of carbon fibres (Sigrafil C10 M250 UNS SGL Group, the Carbon Company). The resulting porous ceramic skeletons, suggest innovative application capabilities mineral nanotubes obtained from halloysite.

8

Corrosion behaviour of aluminium matrix composites reinforced with sintered halloysite nanotubes

Dobrzański L. A., Reimann Ł., Kujawa M., Tomiczek B.

Journal of Achievements in Materials and Manufacturing Engineering

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2015

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Vol. 73, nr 2

92--99

EN

Purpose: The aim of this study was to determine the effect of mass fraction and sintering temperature of the halloysite nanotubes on the corrosion behavior of the infiltrated AlSi12 matrix composites, concerning the matrix alloy. Design/methodology/approach: The corrosion resistance research was done with a potentiodynamic method. Electrochemical corrosion research was made in water centre of 3% NaCl at room temperature. Electrochemical studies of corrosion resistance were performed by determine the open circuit potential and saving the anodic polarization curves by applying to potential changes in the direction of anode and cathode at 1 mV/s. Based on the registered anodic polarization curves were determined: corrosion potential, passive layer breakdown potential, corrosion current density, polarization resistance. The value of corrosion current was determined using the Tafel extrapolation. Findings: Mass fraction of the halloysite nanotubes does not affect the corrosion resistance of the composites as opposed to their sintering temperature. The increase in temperature of a 200°C resulted in a significant reduction in corrosion resistance, but it is still higher than the corrosion of the matrix material. Practical implications: The aluminium alloy matrix composites reinforced with sintered preforms made by sintering halloysite nanotubes are modern materials that could find application in the automotive industry. The mechanical properties are greater than the alloy matrix while retaining a low density. It was necessary to examine the corrosion resistance as one of the important properties of the composites which are exposed to corrosive environments. Originality/value: Beyond the articles of the authors, analysis of mechanical properties and corrosion resistance of the infiltrated AlSi12 matrix composites reinforced by preform made by sintered halloysite were not found in the available literature.

9

Strength parameters of masonry walls in modelling historic constructions

Gołębiewski M., Lubowiecka I., Kujawa M.

Civil and Environmental Engineering Reports

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2015

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No. 18

55--63

EN

The paper presents the determination of the basic material properties of a historic brickwork. Experimental studies were used to identify the basic material properties of bricks. The mechanical properties of the masonry, as an orthotropic homogenized material, were calculated. Then, numerical simulations using the Finite Element Method (FEM) were performed to verify the experimental outcomes. Macromodels with element sizes of 40, 20, 10 and 5 mm, and a micromodel with an element size of 5 mm were applied. The results were compared with experimental data and results available in literature.

PL

W artykule przedstawiono metodę określania podstawowych parametrów wytrzymałościowych zabytkowego muru ceglanego. Zastosowano badania eksperymentalne, aby określić podstawowe parametry wytrzymałościowe cegieł. Uzyskane wyniki porównano z wartościami wymienianymi w literaturze. Tak uzyskane wartości wprowadzono do algorytmów homogenizacyjnych umożliwiających obliczenie parametrów wytrzymałościowych muru jako materiału jednorodnego (zhomogenizowanego). Poprawność wykorzystanych metod zweryfikowano opracowując modele numeryczne MES wykorzystujące uzyskane parametry zhomogenizowanego materiału. Zbadano zbieżność modeli o rozmiarach elementów skończonych 40, 20, 10, i 5 mm. Wyniki uzyskane z modeli zhomogenizowanych oraz mikromodelu porównano z wynikami uzyskanymi przez innych badaczy oraz z wynikami eksperymentalnymi.

10

Influence of technological parameters on additive manufacturing steel parts in Selective Laser Sintering

Król M., Kujawa M., Dobrzański L.A., Tański T.

Archives of Materials Science and Engineering

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2014

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Vol. 67, nr 2

84--92

EN

Purpose: The investigations have been carried out on test pieces of 316L stainless steel parts fabricated by Selective Laser Sintering technique. The effect of selective laser sintering parameters such as power output, laser distance between the points sintered metal powder during additive manufacturing as well as the orientation of models relative to the laser beam and substrate on the roughness, surface morphology and wear resistance of manufactured models were performed. Design/methodology/approach: To fabricate 316L stainless steel parts, the method using selective laser sintering (SLS) technique, using Renishaw AM 125 machine is utilised. Wear resistance, roughness and surface morphology of SLS produced samples prepared via different process parameters are investigated. Findings: The results show that the wear resistance and surface morphology are strongly influenced by orientation of the parts relative to the laser beam, power output of laser and laser distance between the points sintered metal powder during additive manufacturing. Research limitations/implications: In the nearest future, studies will be conducted to establish influence of laser parameters such as scan speed, focus offset, exposure time, diameter of laser beam and hatch parameters such as hatch type and hatch distance on the quality and density of AM steel parts. Practical implications: Stainless steel is one of the most popular materials used for selective laser sintering (SLS) processing to produce nearly fully dense components from 3D CAD models. Reduction of surface roughness is one of the key research issues within the additive manufacturing technique SLS, since one of the major cost factors is the post processing of surfaces by means of milling, turning, grinding and polishing. Originality/value: This paper can serve as an aid in understanding the importance of technological parameters on quality and wear resistance of manufactured AM parts made by SLS technique.

11

Elastic Distortional Buckling of Thin-Walled Bars of Closed Quadratic Cross-Section

Kujawa M., Szymczak C.

Mechanics and Mechanical Engineering

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2013

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Vol. 17, nr 2

119--126

EN

In this study a thin–walled bar with closed quadratic cross-section is considered. The elastic stability of axially compressed bar related to the cross–section distortion is investigated. The governing differential equation is derived with aid of the principle of stationary total potential energy. The critical load for the simply supported bar is found in analytical form and it is compared with the FEM solution. Sufficient accuracy of the results is worth of noticing.

12

Properties of stainless steel based on ferritic steel X6Cr13 made by powder metallurgy

Dobrzański L. A., Kujawa M.

Archives of Materials Science and Engineering

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2013

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Vol. 64, nr 2

135--143

EN

Purpose: of this paper is to define influence of different concentration of reinforcement in form of X2CrNiMo25-7-4 steel powder on the properties of sintered ferritic stainless steel X6Cr13. Design/methodology/approach: In presented study, material for investigation was manufactured by powder metallurgy from ferritic powders with appropriate contribution of austenitic-ferritic stainless steels powders. Prepared mixes have been pressed by cold isostatic pressing (CIP) at 350 MPa and sintered in vacuum furnace at 1250°C for 1 h. Obtained samples were examined by scanning electron microscopy (SEM), X-ray diffraction analysis and confocal microscopy for depth of the wear traces observation. Properties like porosity, density, wear resistance, macro- and microhardness were evaluated. Findings: Researches show that addition of 5-15% powder duplex stainless steel caused the significant increase in hardness and microhardness of X6Cr13 steel. Small amount of reinforcement powder improved the value of wear resistance of base material. Research limitations/implications: Contribute to study the properties of materials with the base of ferritic stainless steel reinforced by X2CrNiMo25-7-4 particles using powder metalurgy. The next step for research will be to examine tensile properties and corrosion resistance which is a fundamental property required for the described steels. Practical implications: Development of a new type of materials applicable in the industry which are characterized by a higher wear resistance and good mechanical properties. Originality/value: The obtain results show the possibility of creation the newest materials base on X6Cr13 steels with better properties caused by proper volume fraction of reinforcement.

13

Torsional Buckling of Restrained Thin-Walled Bars of Open Bisymmetric Cross-section

Kujawa M.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2012

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Vol. 16, No 3-4

301--306

EN

The problem of torsional budding of restrained thin-walled bars of an open constant bisymmetnc cross-section was solved using the minimum total stationary elastic energy condition (J. S. Przemieniecki 1968 Theory of Matrix Structural Analysis McGraw-Hill, New York) and the Newton-Raphson method (S. C. Chapra and R. P. Canale 1998 Numerical Methods for Engineers McGraw-Hill Book Company). The consideration was restricted to the elastic structures. The example presented in the paper helps to assess the correctness of the proposed solution. This article is an addition to the author's considerations contained in M Kujawa 2012 TASK Quart. 16 (1/2) 5.

14

Torsion of Restrained Thin-walled Bars of Open Constant Bisymmetric Cross-section

Kujawa M.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2012

|

Vol. 16, No 1-2

5-15

EN

Elastic and geometric stiffness matrices were derived using Castigliano’s first theorem, for the case of torsion of restrained thin-walled bars of open constant bisymmetric cross-section. Functions which describe the angles of torsion were adopted from the solutions of the differential equation for restrained torsion. The exact solutions were simplified by expanding them in a power series. Numerical examples were taken from Kujawa M 2009 Static and Sensitivity Analysis of Grids. . . 97, GUT Publishing House, and Szymczak C 1978 Engineering Transaction 26 323. Convergence of the solutions was analyzed using the matrices derived for torsion angles, warping, bimoments and critical forces.

15

Distorsional Analysis of I-section Beam

Kujawa M.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

|

2012

|

Vol. 16, No 1-2

17-22

EN

An elastic stiffness matrix was derived in the case of distortion of a restrained thin- walled I-section beam using the minimum total stationary elastic energy condition (Przemie- niecki J S 1968 Theory of Matrix Structural Analysis, McGraw-Hill, NY). The function describ- ing the angle of distortion was adopted form the solution of differential equation in the case of restrained distortion. The example presented in the paper helps to assess the correctness of the proposed solution. The proposed elastic stiffness matrix is applicable for solving distortion problems of bar structures composed of thin-walled members.

16

Modelowanie procesów o różnych skalach czasowych na przykładzie instalacji Clausa do odzysku siarki

Jaworski M., Kujawa M., Piotrowski R., Duzinkiewicz K.

Modelowanie Inżynierskie

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2012

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T. 14, nr 45

161--170

PL

W przemyśle petrochemicznym odzyskiwanie siarki stanowi jeden z ważniejszych procesów towarzyszących kompleksowemu przetwarzaniu ropy naftowej i substancji pochodnych. W artykule przedstawiono matematyczny model instalacji odsiarczania gazów Clausa wraz z układem sterowania. Wnikliwa analiza procesów zachodzących w obiekcie pozwoliła zaproponować metodykę budowy i strukturę modelu adekwatną do potrzeb syntezy układu sterowania. Model ujmuje odwzorowanie procesów chemicznych i pozwala badać zmiany ich przebiegu w wyniku działania układu sterowania. Ze względu na różne skale czasowe dynamiki modelowanych procesów zachodzących w instalacji i elementów układu sterowania, zaproponowano model w części statyczny, a w części dynamiczny. Przedstawiono inżynierską metodę optymalizującej estymacji parametrów modeli. Zaprezentowane zostały wyniki weryfikacji modeli na podstawie danych obiektowych. Opracowane modele stanowią proste, użyteczne narzędzie analizy, pozwalające na badanie przebiegu zmiennych procesów fizykochemicznych oraz sygnałów związanych ze sterowaniem instalacją. Wskazano na ich przydatność przy wykrywaniu nieprawidłowości pracy elementów wykonawczych układu sterowania. W analizowanym obiekcie niezgodnie z założeniami pracował jeden z zaworów doprowadzających powietrze do instalacji. Po zdiagnozowaniu i usunięciu nieprawidłowości uzyskano poprawę jakości działania całego obiektu.

EN

Sulfur recovery is one of the most important processes accompanying crude oil refining and derivative substances processing in petrochemical industry. In the paper a mathematical model of Claus Sulfur Recovery Unit (SRU) together with its control system has been presented. Model formulation has been preceded by the thorough research on a real object which allowed to create an adequate, for the purpose of synthesis of control system, representation of chemical phenomena and their changes as a result of the control system functioning. Due to different time scales of dynamics of modeled processes, partially dynamic and static models have been proposed. An engineering optimizing method for model parameters estimation has been presented. Results of models verification were also presented. They were based on the data collected from object. Developed models provide a simple and useful analysis tool which allows to examine physicochemical processes and signals associated with the control of the installation. The paper pointed out models usefulness in detection of abnormalities in the Claus’ installation operationas well as in improvement of their performance.

17

Study of the third order nonlinear optical properties of Zn1-xMgxSe and Cd1-xMgxSe crystals

Derkowska B., Firszt F., Sahraoui B., Marasek A., Kujawa M.

Opto-Electronics Review

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2008

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Vol. 16, No. 1

8-11

EN

Third order nonlinear optical susceptibilities χ³ of ternary Zn₁-xMgxSe and Cd₁-xMgxSe crystals have been measured using standard degenerate four-wave mixing (DFWM) method at 532 nm. The nonlinear transmission technique has been applied to check if our crystals exhibit two-photon absorption. The studied Zn₁-xMgxSe and Cd₁-xMgxSe solid solutions were grown from the melt by the modified high-pressure Bridgman method. For both crystals the energy gap increases with increasing Mg content. In the case of Zn₁-xMgxSe, it was found that the value of third order nonlinear optical susceptibility χ³ decreases with increasing Mg content. An explanation of this behaviour results from the dependence of optical nonlinearities on the energy band gap Eg of the studied crystals. In the case of Cd₁₋xMgxSe with low content of Mg, no response was observed for the studied wavelength since the energy gap in such crystals is smaller than the photon energy of the used laser radiation. It was also found that the value of third order nonlinear optical susceptibility χ³ for Cd₀.₇₀Mg₀.₃₃ is higher than for Zn₀.₆₇Mg₀.₃₃Se. This behaviour can be understood if one take into consideration that the free carrier concentration in Cd₁₋xMgxSe samples is about four orders of magnitude higher than that in Zn₁₋x MgxSe ones with comparable Mg content respectively. It is commonly known that when the electric conductivity increases, the values of nonlinear optical properties increase. From the performed measurements one can conclude that the incorporation of Mg as constituent into ZnSe and CdSe crystals leads to a change of the third order nonlinear optical susceptibilities.

18

Analiza statyczna belek załamanych w planie zbudowanych z prętów cienkościennych o przekrojach otwartych

Kujawa M., Szymczak C.

Zeszyty Naukowe Politechniki Gdańskiej. Budownictwo Lądowe

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2006

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nr 58

255-262

EN

Grids composed of the thin-walled beams of open cross-section are very often used in civil engineering structures and in various machines and vehicles. In the present research we propose the finite element model for grids consisting of: in the region between grid nodes, thin-walled elements based on the classical assumptions of the theory of thin-walled beams of non-deformable cross-section; in the region of nodes, superelements composed of flat shell elements. The superelement stiffness matrix can be determined with the help of the ABAQS software package, by treating the nodal zone as a complex system of plates subdivided into a suitable number of S4R shell elements. In authors' opinion the influence of bimoment stresses is one of important

19

Reduction of steel chimney vibrations with a pendulum damper

Jankowski R., Kujawa M., Szymczak Cz.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2004

|

Vol. 8, No 1

71-78

EN

Karman vortices observed around chimneys may induce dangerous structural vibrations at certain wind velocities. The aim of this paper is to analyse the effectiveness of a pendulum damper in reducing vibrations of a steel chimney. A two-degree-of-freedom non-linear model is used to simulate the behaviour of the structure equipped with a damper. The results of the study show that the use of a pendulum with tuned frequency leads to significant reduction in structural response.

20

Analiza statyczna rusztów zbudowanych z prętów cienkościennych

Szymczak C., Kujawa M.

Konstrukcje Stalowe

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2003

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nr 5 spec.

CD-CD

PL

Praca dotyczy analizy statycznej cienkościennych konstrukcji rusztowych poddanych obciążeniom powodującym skręcanie ich elementów. Przedstawiono metodę modelowania układów rusztowych z wykorzystaniem superelementów węzłowych, w której podatny węzeł modelowany jest za pomocą elementów płytowo-tarczowych MES. Rozważania zilustrowano prostym przykładem liczbowym. Dla porównania zestawiono wyniki analizy dla trzech różnych modeli numerycznych.