Wyniki wyszukiwania - Biblioteka Nauki

1

Analysis of Slope Creep in the Example of a Landslide Slope in Koronowo near Bydgoszcz

100%

Zabuski L.

Archives of Hydro-Engineering and Environmental Mechanics

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2018

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tom Vol. 65, nr 1

3--10

EN

This paper presents the results of a numerical simulation of a slope deformation process. The landslide slope “Grabina” inKoronowo near Bydgoszcz (Poland) serves as an example.Aslope profile located in the central part of the slope, between the main scarp and the toe of the landslide, was selected. The average dip of the slope is about 10, and its length is approximately 55 m. Elasticity, plasticity and viscosity properties were taken into account in the model of the soil mass that composes the slope. The visco-elastic properties are described by the Burgers model (Mainardi and Spada 2011), and the plastic ones by the Coulomb-Mohr law.Anumerical simulation was carried out by the computer code FLAC2D in the plane strain state with the assumption of the Lagrange routine. The model was discretized taking into account the results of inclinometric measurements, which proved that the slide movement was concentrated in a narrow loam zone of 0.5–1.0 m thickness. No tests of the viscosity parameters were performed, so they were determined by the back analysis and a trial and error method. The calculation results were verified by comparison with the displacement measured by the inclinometric method in three boreholes. The analysis performed demonstrated the possibility of approximating and forecasting landslide displacements by the combined Burgers and Coulomb-Mohr models.

2

Modelling the time-dependent behaviour of soft soils

100%

Staszewska K. , Cudny M.

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2020

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tom Vol. 42, nr 2

97--110

EN

Time dependence of soft soils has already been thoroughly investigated. The knowledge on creep and relaxation phenomena is generally available in the literature. However, it is still rarely applied in practice. Regarding the organic soils, geotechnical engineers mostly base their calculations on the simple assumptions. Yet, as presented within this article, the rate-dependent behaviour of soft soils is a very special and important feature. It influences both the strength and the stiffness of a soil depending on time. It is, thus, significant to account for time dependence in the geotechnical design when considering the soft soils. This can result in a more robust and economic design of geotechnical structures. Hence, the up-to-date possibilities of regarding creep in practice, which are provided by the existing theories, are reviewed herein. In this article, we first justify the importance of creep effects in practical applications. Next, we present the fundamental theories explaining the time-dependent behaviour of organic soils. Finally, the revision of the existing constitutive models that can be used in numerical simulations involving soft soils is introduced. Both the models that are implemented in the commercial geotechnical software and some more advanced models that take into account further aspects of soft soils behaviour are revised. The assumptions, the basic equations along with the advantages and the drawbacks of the considered models are described.

3

Creep analysis of M1E copper and PA6 aluminium alloy subjected to prior plastic deformation

100%

Kowalewski Z. L.

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tom Vol. 43 nr 2

241--256

EN

The influence of prior plastic deformation on the creep process is studied for copper and an aluminium alloy. Variations of basic creep parameters due to differences in temperature of realized tests are also taken into account. Moreover, the paper reports the prestraining effects depending on the type of prior deformation. It is shown for both materials that, depending on the deformation history, the basic creep parameters may attain values which are more beneficial from the engineering point of view than those for the non-prestrained material determined. It is also shown that, in some cases, prior plastic deformation may lead to detrimental effects expressed, for example, by reduction of the lifetime.

PL

W pracy przedstawiono badania dotyczące wpływu wstępnej deformacji plastycznej na proces pełzania miedzi i stopu aluminium. W doświadczeniach uwzględniono wplyw zmian temperatury na podstawowe parametry pełzania. Omawiane są również efekty zależne od rodzaju wstępnej deformacji. Dla obu badanych materiałów pokazano, że zależnie od historii deformacji podstawowe parametry pełzania mogą ulegać poprawie w stosunku do parametrów otrzymanych dla takich samych materiałów testowanych w stanie dostawy. Przedstawiono również warunki, przy których wspomniane parametry ulegają istotnemu pogorszeniu (np. obniżeniu żywotności).

4

Modelowanie zmian odkształcenia pełzania, geometrii przekroju i naprężeń w zowalizowanych rurach pracujących w warunkach pełzania

100%

Augustyniak M. , Kwintowski K. , Łopata S.

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tom T. 34, nr 2

229-240

PL

Względy bezpieczeństwa i potrzeba określania trwałości wysokociśnieniowych rurociągów parowych wymagają, kontroli diagnostycznej w ciągu całego okresu ich użytkowania. Jednym z ważniejszych składników są pomiary odkształceń związanych z pełzaniem. Wykorzystując wyniki prowadzonych od wielu lat badań pokazano przykłady eksploatacyjnych krzywych pełzania rurociągów wykonanych ze stali Cr-Mo i Cr-Mo-V. Stwierdzono, ze osiągane odkształcenie pełzania, po tym samym czasie pracy, jest tym większe, im wyższa jest owalność początkowa przekroju poprzecznego elementu. Z technicznego punktu widzenia dotyczy to elementów z owalnością wyższą od 2%. W ich przypadku odkształcenia pełzania wyznaczane na podstawie pomiarów średnic w kierunkach wzajemnie prostopadłych znacznie się różnią. Do symulacji pełzania takich elementów wykorzystano program ANSYS Multiphysics, uzyskując zadowalającą zgodność z eksperymentem.

EN

With regard to safety and necessity of durability estimations, high-pressure steam pipelines require an efficient diagnostic procedure during whole operating period. One of the most important components of the standard procedure is measuring creep deformations. In this paper we present some representative examples of creep curves for pipelines made of Cr-Mo and Cr-Mo-V steels, obtained during several years of operation. It is confirmed that creep strain after the same operation time is higher when the initial ovality of cross-section element is more significant. From a technical point of view, it concerns the elements with ovality higher than 2%. In their case the creep strain assessment based on diameter measurements in two perpendicular directions, i.e. for smallest and largest diameters, varies significantly. Acceptable conformity between results of ANSYS Multiphysics numerical simulations of creep-ovalised pipe and experimental data was obtained.

5

Comparison of various models of creep coupled with damage evolution

100%

Bielski M. , Badur J.

Zeszyty Naukowe Politechniki Białostockiej. Mechanika

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2001

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tom Z. 24

49--56

EN

Four different creep models coupled with damage calibrated for P91 steel and implemented within the commercial ABAQUS code have been analysed for different element of live steam piping system within the supercritical power plant.

PL

Cztery modele pełzania ze zniszczeniem zostały wykalibrowane dla stali P91 a następnie zaimplementowane w programie ABAQUS. Dokonano obliczeń różnych elementów rurociągu pary świeżej siłowni nadkrytycznej.

6

Numerical investigation of creep behaviour of high-temperature steam turbine compone

100%

Banaszkiewicz M.

Transactions of the Institute of Fluid-Flow Machinery

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2012

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tom nr 124

5--15

EN

The paper presents a model for creep basing on the so-called characteristic creep strain. It illustrates its application in computations of old steam turbines components. The presented model is a modification of the Norton model which relates the stress exponent to the creep rupture strength and current stress. Creep strain is a function of the above two quantities, i.e., rupture strength and current stress, and acharacteristic creep strain which is material constant for a given time and temperature. Computational examples regard the rotating and pressure components analysed using the finite element method.

7

Life prediction for alloy steel pipeline under creep conditions

100%

Comandar C. , Amariei N. , Leon D.

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1999

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tom Vol. 4, no spec.

75-78

EN

This paper presents the research of the authors did to determine the current state of two steam pipe-lines after 100 000 hours in function at 500°C and 10MPa. Chemical and metallographic analyses, mechanical tests and creep failure tests have been performed. The results of the creep tests were extrapolated by means of Larson-Miller method. The paper presents graphics of results obtained. The behaviour of the studied materials is interpreted from the residual life assessment.

8

The influence of material aging on the structural behavior of a flexible roof with a polymer membrane shell

100%

Chesnokov A. V. , Mikhailov V. V. , Dolmatov I. V.

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2021

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tom Vol. 21, No. 1

13--24

EN

The roof structure considered in the research consists of continuous cables and a number of spreaders forming a three-dimensional frame. The frame is covered with a polymer membrane made of flexible architectural fabrics. The elements of the roof are compact and suitable for transportation to remote construction sites. The roof also has advantages for developing areas with harsh climatic conditions. The flexible elements of the roof, however, only provide transmission of tensile forces. Under compression, cables slacken and the membrane becomes wrinkled. Pre-tension of the flexible elements, which is introduced to retain the operability of the roof, tends to gradually diminish due to material aging. The aging results in the alteration of strength properties and creep elongation of the structural elements. It induces membrane tearing on local areas. Force alteration in primary structural members is examined in the present study, with statistical methods used for data analysis. They include significance hypothesis testing and correlation coefficients estimation. The data are obtained by the Finite Element simulation of the roof using EASY-2020 software. The results of the work may be used for life expectancy assessment of flexible roof structures, providing important information for the preliminary design stage. The work contributes to the safety enhancement of cable-membrane structures and the expansion of their scope in permanent building constructions.

9

Effect of Time History on Long-Term Deformation of Gypseous Soils

88%

Fattah M. Y. , Al-Shakarchi Y. J. , Al-Numani H. N.

Studia Geotechnica et Mechanica

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2022

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tom Vol. 44, nr 3

198--210

EN

The time-dependent behavior of three gypseous soils was investigated. The soils had gypsum content of 66%, 44%, and 14.8%. The mineralogical and chemical properties of the soils were determined. Two series of tests were performed. In the first, collapsibility characteristics were investigated for a long period (60 days) by conducting single and double oedometer tests. In the second series, the effect of relative density on collapse with time was investigated. The samples were compacted to 40%, 50%, and 60% relative density and then tested. The results of collapse tests showed that the relationship between the strain and logarithm of effective stress has two vertical lines. The first one represents the collapse settlement taking place within 24 h, while the second one represents the long-term collapse. The collapse potential (CP) in both single and double oedometer tests increases when the gypsum content increases from 14.8% to 66% and when the initial void ratio increases. The CP–logarithm of time relationship for soaked samples prepared at different relative densities under 800 kPa indicated that the CP increased with time for the soil sample compacted at 60% relative density and the increase was higher than those compacted at 40% and 50% relative density. The curves started with a straight line and then a concave downward curve was observed with a high strain. For samples compacted at 40% and 50% relative densities, the curves were interrupted by little soil collapses, while the third curve exhibited smooth relation following the collapse.

10

Creep buckling of wedge-shaped floating ice plate

88%

Staroszczyk R. , Hedzielski B.

Engineering Transactions

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2004

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tom Vol. 52, iss.1-2

111-130

EN

The paper is concerned with the problem of creep buckling of a floating ice plate pressin against a rigid, vertical-walled, engineering structure of a finite lenght. The plate is modelled as a truncated wedge of a semi-infinite length and constant thickness, resting on a liquid base and subjected to transverse bending due to the elastic reation of the base and in-plane axial compression due to wind and water drag forces. The ice is treated as a viscous materail, with the viscosity varying with the depth of the ice cover. The results of numerical calculations, carried out by the finite element method, show the evolution of creep buckles in the plate, and also ilustrate the behaviour of the ice cover at different levels of the in-plane axial loading, at different temperatures across the ice, and for different geometries of he wedge-shaped plate.

11

Determination of quasi-filtration phase of consolidation based on experimental and theoretical course of the uniaxial deformation and distribution of pore pressure

88%

Olek B. S. , Woźniak H.

Geology, Geophysics and Environment

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2016

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tom Vol. 42, no. 3

353--363

EN

In this work the consolidation characteristics of the experimental and theoretical process of consolidation was studied. The analyses were carried out on the basis of the axial soil deformation progress and the pore pressure dissipation. The applied methodology gives possibility for the simultaneous comparison of the experimental and theoretical consolidation data and verification of the validity of calculated values of coefficient of consolidation, estimated using different methods. The aim of this research was to put some light on the quasi-filtration phase of consolidation. The results of consolidation studies on five high quality paste samples prepared from Krakowiec clays showed that the quasi-filtration occurs only in specific stages of the whole process. The analysis of changes in coefficient of consolidation depending on the degree of consolidation, enables the separation of the region of quasi-fixed values of c v, which corresponds to the quasi-filtration phase of consolidation.

12

Wpływ naprężeń cyklicznych na proces pełzania stopu aluminum przy złożonych obciążeniach

88%

Jermołaj W.

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tom Z. 73

71-76

PL

W pracy przedstawiono wyniki badań pełzania, stopu aluminium pod działaniem obciążeń statycznych oraz obciążeń cyklicznych w złożonym stanie obciążenia, tj. rozciąganie ze skręceniem. Zbadano wpływ naprężeń cyklicznych na proces tworzenia się odkształceń pełzania przy stałym współczynniku amplitudy intensywności naprężeń. W celu porównania warunków kumulowania w czasie ostatecznych odkształceń przy statycznych i cyklicznych obciążeniach, wyznaczono względne trwałości, określone syosunkiem trwałości zmęczeniowej do trwałości pełzania dla ustalonych wartości naprężeń zredukowanych. Sformułowano kryterium naprężeniowe, opisujące procesy zniszczenia przy pełzaniu i dynamicznym pełzaniu.

EN

In the paper the results of creep testing of aluminium alloy under static and also cyclic loading in complex load states for tenison and torsion are presented. It was tested the effect of cyclic stress on process taking of creep deformations for constant value of stress intensity amplitude coefficient. In an aim of comparison of accumulation conditions at time of final strains by static and cyclic loading it was found relative life determined by ratio of fatigue life to creep life.It made for fixed value of reduced stress. It also formulated stress criterion describing rupture processes of creep and fatigue.

13

Effect of Rhenium Addition on Microstructures and Mechanical Properties of Oxide Dispersion Strengthened Ferrtic Steels

88%

Noh S. , Kang S. H. , Kim T. K.

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2020

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tom Vol. 65, iss. 4

1261--1264

EN

In this study, to investigate effects of rhenium addition on the microstructures and mechanical properties, 15Cr-1Mo ODS ferritic steels with rhenium additions were fabricated by the mechanical alloying, hot isostatic pressing, and hot rolling processes. Unremarkable differences on grain morphologies and nano-oxide distributions were estimated in the microstructure observations. However, the ODS ferritic steels with 0.5 wt.% rhenium showed higher tensile and creep strengths at elevated temperature than that without rhenium. It was found that rhenium is very effective to improve the mechanical properties.

14

Numerical creep analysis of FGM rotating disc with GDQ method

88%

Zharfi H. , Toussi H. E.

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tom Vol. 55 nr 1

331--341

EN

Rotating discs are the vital part of many kinds of machineries. Usually, they are operating at relatively high angular velocity and temperature conditions. Accordingly, in practice, the creep analysis is an essential necessity in the study of rotating discs. In this paper, the time dependent creep analysis of a thin Functionally Graded Material (FGM) rotating disc investigated using the Generalized Differential Quadrature (GDQ) method. Creep is described with Sherby’s constitutive model. Secondary creep governing equations are derived and solved for a disc with two various boundary conditions and with linear distribution of SiC particles in pure Aluminum matrix. Since the creep rates are a function of stresses, time and temperature, there is not a closed form solution to these equations. Using a solution algorithm and the GDQ method, a solution procedure for these nonlinear equations is presented. Comparison of the results with other existing creep studies in literature reveals the robustness, precision and high efficiency beside rapid convergence of the present approach.

15

Effects of hydrogen induced elastic and plastic straining on its transport in Al

88%

Łunarska E. , Chernyayeva O.

Advances in Materials Science

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2007

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tom Vol. 7, nr 1(11)

153-159

EN

Hydrogen entering at cathodic polarization produces the straining of Al. In the course of increased polarization, the elastic strain causing the up-hill diffusion of hydrogen present in metal and then the plastic deformation creating of hydrogen traps have been introduced. As a result, the unusual appearance of hydrogen permeation transients and the retardation of hydrogen transport and its accumulation within the plastically deformed metal occur at the low and at the high polarization, respectively. The supersaturation of surface layers with hydrogen or the formation of the patchy hydride like layer have been discussed to be the source of the observed metal straining.

16

The service life of the repair welded joint of Cr-Mo / Cr-Mo-Y

88%

Sroka M. , Zieliński A. , Mikuła J.

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tom Vol. 61, iss. 3

1315--1320

EN

The service life of the repair welded joint of Cr-Mo / Cr-Mo-Y This paper presents the evaluation of the service life of dissimilar repair welded joint from Cr-Mo/Cr-Mo-V steel after 200,000 h service under creep condition. The investigations of microstructure using scanning electron microscopy, investigations of mechanical properties at room and elevated temperature as well as creep tests of the basic material from Cr-Mo and Cr-Mo-V steel and welded joint from these steels were carried out. The investigations allowed the tune of further safe operation of the repair welded joint in relation to the residual life of the materials to be determined. The evaluation of residual life and disposable residual life, and thus the estimation or determination of possible time of further safe operation, is crucial when the elements are operated much beyond the design work time.

17

Time-dependent thermo-elastic creep analysis of thick-walled spherical pressure vessels made of functionally graded materials

88%

Kashkoli M. D. , Nejad M. Z.

Journal of Theoretical and Applied Mechanics

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2015

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tom Vol. 53 nr 4

1053--1065

EN

Assuming that the thermo-elastic creep response of the material is governed by Norton’s law and material properties, except Poisson’s ratio, are considered as a function of the radius of the spherical vessel, an analytical solution is presented for calculation of stresses and displacements of axisymmetric thick-walled spherical pressure vessels made of functionally graded materials. This analytical solution could be used to study the time and temperature dependence of stresses in spherical vessels made of functionally graded materials. Creep stresses and displacements are plotted against dimensionless radius and time for different values of the powers of the material properties.

18

Assessment of loss in life time of the primary steam pipeline materiał after long-term service under creep conditions

88%

Zieliński A. , Dobrzański J. , Jóźwik T.

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2012

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tom Vol. 54, nr 1

67--74

EN

Design/methodology/approach: For material of the pipeline after long-term service the microstructure investigations in a scanning electron microscope, phase composition analysis of precipitations, hardness measurement at the point where structure was observed and mechanical testing at room temperature were carried out. In addition, the magnetic particle inspections and ultrasonic testing were carried out over the entire volume of the pipeline sample. Findings: The life exhaustion extent of the investigated steel 14MoV6-3 estimated based on the metallographic tests is much higher than the expected one for the investigated steel at the current working parameters of the pipeline. Correct evaluation of the pipeline material condition during the periodic diagnostic testing, including but not limited to that performed by the matrix replica method, allows the excessive loss in life time of the material to be revealed and the reason for premature destruction of the pipeline components to be diagnosed and removed early enough. Practical implications: The presented method can be used for evaluation and qualification of structural changes in power station boiler components operating under creep conditions. Originality/value: The presented results of changes in the mechanical properties, structure and in the precipitation processes are applied to evaluate the condition of the elements in further industrial service.

19

Badania procesu pełzania materiałów konstrukcyjnych na poziomie makroskopowym

75%

Kowalewski Z. L.

|

2001

|

tom nr 2

11-16

PL

W pracy przedstawiono główne mechanizmy kontrolujące proces odkształcenia metali wywołany stałym obciążeniem powodującym zachodzenie zjawiska pełzania. Na przykładzie badań wykonanych dla miedzi omówiono problem wpływu wielkości ziarna na mechanizmy deformacyjne przy pełzaniu oraz na makroskopowe parametry tego procesu.

EN

Main mechanisms controlling the process of determination of metal caused by permanent load leading to the creep. An example of investigating a copper test-piece permitted to handle the problem of how the grain size influences the deformating mechanisms during the creep and the microscopic parameters of that process.

20

Badania relaksacji naprężeń stosu metalicznego z gradientem reologicznym

75%

Knych T. , Kwaśniewski P. , Mamala A.

Rudy i Metale Nieżelazne

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2005

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tom R. 50, nr 10-11

595-602

PL

Procesy pełzania i relaksacji naprężeń to podstawowe sposoby ujawniania cech reologicznych materiałów w warunkach niespełnionego kryterium naprężeniowego. Chociaż znane są charakterystyki relaksacji naprężeń pojedynczych materiałów jako funkcje naprężenia, temperatury i czasu, to brak jest w literaturze przedmiotu wyników badań relaksacji naprężeń w układach (stosach) zbudowanych z materiałów o zróżnicowanych cechach lepkosprężystych. Analiza stanu reologicznego takich układów nie jest prosta bowiem powierzchnie zmian własności lepkich i sprężystych ulegają przemieszczaniu, co wprowadza dodatkowy stopień nieokreśloności układu. W pracy przeprowadzono rozważania dotyczące zmian stanu naprężenia w stosie, spowodowanych relaksacją naprężeń, jaka zachodzi w jego elementach. Wyprowadzono wzory umożliwiające określenie modułu sprężystości oraz charakterystyk relaksacji naprężeń w stosie z dyskretnym gradientem reologicznym. Zamieszczono wyniki badań relaksacji naprężeń stosów zbudowanych z materiałów o różnej odporności reologicznej. Procesy reologiczne zachodzące w stosach posiadają szczególnie znaczenie praktyczne, ujawniają się bowiem w układach połączeń elementów o różnych własnościach, w których, z pewnych względów, wymagana jest stabilna siła docisku.

EN

Creep and stress relaxation are essential ways of revealing rheological features of materials in conditions of the unfulfilled yield criterion. Stress relaxation characteristics of homogeneous material, as a function at stress temperature and time are well known we notice the lack of concerning deliberations on the stack built from two different viscoelastic materials. Rheological description of stack isn 't easy due to changes of elastic and viscous properties surfaces motions, with causes additional troubles. Deliberations concerning changes in the state of the tension in the stack were carried at work, caused stress relaxation as and is setting in his elements. Equation for module of the resilience and stress relaxation characteristics in the stack with the rheological gradient calculation. Findings of examinations were printed stress relaxation of stacks built from materials about the different rheological resistance. Rheological process setting in stacks they have particularly a practical significance, because they are becoming apparent in arrangements of connections of elements about different properties, which the stable force of pressure is required from sure accounts in.