Thematische Bibliographien / Swelling stresses

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Auswahl der wissenschaftlichen Literatur zum Thema „Swelling stresses“

Autor: Grafiati

Veröffentlicht am 25. Mai 2024

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Zeitschriftenartikel zum Thema "Swelling stresses"

Bathija, Arpita Pal, Haiyi Liang, Ning Lu, Manika Prasad und Michael Lee Batzle. „Stressed swelling clay“. GEOPHYSICS 74, Nr. 4 (Juli 2009): A47—A52. http://dx.doi.org/10.1190/1.3131385.

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Clay minerals are present in most sedimentary rocks. They find applicability in a wide range of disciplines, such as material, soil, earth, environmental, and biological sciences. Despite their abundance and use, swelling of clays under stress has not received enough scientific attention. We used a two-method approach, consisting of molecular simulation and nanoindentation measurements on montmorillonite. Our analyses of the molecular structure of montmorillonite at various stresses and hydration states showed that swelling behaves in a nonlinear way with stress. Nanoindentation results of Young’s modulus agree with our simulation results, showing the importance of the interlayer in composite clay properties.

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Nah, C., G. B. Lee, C. I. Lim, J. H. Ahn und A. N. Gent. „Swelling of Rubber under Nonuniform Stresses and Internal Migration of Swelling Liquid When the Stresses Are Removed“. Macromolecules 44, Nr. 6 (22.03.2011): 1610–14. http://dx.doi.org/10.1021/ma102528t.

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Papanastasiou, Tasos C., Dionissios G. Kiriakidis und Theodore G. Nikoleris. „Extrudate Swelling: Physics, Models, and Computations“. Applied Mechanics Reviews 48, Nr. 10 (01.10.1995): 689–95. http://dx.doi.org/10.1115/1.3005050.

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Viscous, viscoelastic, or elastic normal stresses are superimposed to pressure within flowing fluids. These stresses act normal to the boundaries of the flow that may deform depending on their modulus or viscosity. At absolutely rigid boundaries of infinite modulus of elasticity any boundary deformation and therefore any fluid expansion or swelling is surpressed (eg, flow in rigid pipes, annuli, channels). Elastic boundaries (eg, flow in veins and arteries, flow by membranes, around inflating/deflating balloons) deform under the action of normal stresses, allowing expansion or swelling of fluid. The same mechanism prevails in lubrication, where pressure and superimposed normal viscoelastic stresses keep surfaces in relative motion apart, with simultaneous increase in load capacity. Viscous boundaries (eg, liquid jet in air or in immiscible liquid, slow extrusion of viscoelastic liquids from dies, expanding/collapsing air-bubbles or liquid-droplets) are displaced by flowing adjacent immiscible fluids, allowing swelling or imposing contraction depending on relative rheological characteristics. Thus, the kind of swelling examined here is independent of density, ie, incompressible, and is due to the action of normal stresses against the boundary that is imposed either by adjacent deformable obstacles or else by surface tension. The resulting swelling is dynamic (ie, it initiates, changes and ceases with the flow) and can be made permanent by solidification, crystallization or glassification. The most profound form of incompressible swelling is the extrude swelling that controls the ultimate shape of extruded parts. Incompressible swelling is enhanced by the ability of macromolecules to deform and recover (eg, viscoelastic) and by the design of flow conduits to impose sharp transitions of deformation modes (eg, singular exit flows). The same swelling is reduced by the ability of molecules (or fibers in fiber-suspensions) to align with the flow streamines, as well as any tendency of solid-like structure formulation (eg, viscoplastic).

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Khrapatova, I. V., und O. V. Krotov. „THE ANALYSIS OF THE STRESS-STRAIN STATE OF THE SYSTEM «BASEMENT - PILE FOUNDATION – STRUCTURE» CONSIDERING SWELLING PROPERTIES OF SOILS“. ACADEMIC JOURNAL Series: Industrial Machine Building, Civil Engineering 2, Nr. 49 (17.10.2017): 54–60. http://dx.doi.org/10.26906/znp.2017.49.824.

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This work analyzes factors affecting swelling soils and presents a calculation algorithm of structure on swelling soils base for the plane problem. In this work an analysis of the factors influencing the swelling of soils is made, the algorithm for calculating the structure with the base with swellable soils for a plane problem is given. At the same time, the swelling process is considered as an additional influence, close in nature to temperature, and the swelling soil is considered a material having orthotropic properties. The value of the relative swelling depends on the level of the stress state, while the value of the main stresses is compared with the magnitude of the pressure of swelling. Therefore, to determine the deformation characteristics of the swelling soil, several variants of the stressed state of the soil have to be considered. The effectiveness of the obtained solution has been verified according to the example for pile foundations.

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Makhnenko, O. V., I. V. Mirzov und V. B. Porokhonko. „Modelling of residual stresses, radiation swelling and stressed state of in-service WWER-1000 reactor baffle“. Paton Welding Journal 2016, Nr. 4 (28.04.2016): 32–38. http://dx.doi.org/10.15407/tpwj2016.04.03.

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Hall, M. M. „Irradiation creep relaxation of void swelling-driven stresses“. Journal of Nuclear Materials 432, Nr. 1-3 (Januar 2013): 166–74. http://dx.doi.org/10.1016/j.jnucmat.2012.08.015.

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Kowalski, Stefan J., und Andrzej Rybicki. „Drying Induced Stresses in a Swelling Porous Wall“. Transport in Porous Media 57, Nr. 1 (Oktober 2004): 35–48. http://dx.doi.org/10.1023/b:tipm.0000032743.55654.ed.

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Kowal, M., und S. J. Kowalski. „Experimental Investigation of Water Soaked Wood at Uniaxial and Biaxial States of Stress“. Applied Mechanics Reviews 48, Nr. 10 (01.10.1995): 684–88. http://dx.doi.org/10.1115/1.3005049.

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It is possible to observe a significant difference in swelling strains of unstressed and stressed water soaked wood. This paper points out that the swelling strains depend not only on the magnitude of stress in wood but also on the kind of stress state. Our main aim is to investigate the relation between various states of stress and the swelling strains in water soaked wood. Three different states of stress are studied: tension in the radial direction, compression in the tangential direction with respect to the growth rings, and both these stresses acting together (biaxial stress). Some weighty conclusions follow from the investigations. The main one is that, although the mechanical strains alone are negligibly small compared to the free swelling strains, the coupled mechanical-swelling strains, being a function of the stress state and the moisture content, have a great significance in total strains of water soaked wood.

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Breslavsky, Dmytro. „Influence of stresses on deformation process under the irradiation creep and swelling“. Bulletin of the National Technical University «KhPI» Series: Dynamics and Strength of Machines, Nr. 2 (31.12.2021): 23–28. http://dx.doi.org/10.20998/2078-9130.2021.2.245529.

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Approaches for describing the deformation of structural elements made from the material, in which radiation creep and swelling strains develop simultaneously, are discussed. The technique for description of irradiation swelling strains, which is used for calculational analysis of stress-strain state arising in structural elements under the joint action of irradiation and thermal-stress fields, is regarded. A complete system of equations of the boundary –initial value problem is presented, in which elastic and thermal strains, strains of radiation creep and swelling are taken into account. Numerical modelling was carried out using the specialized software FEM Creep, in which the boundary value problem is solved by the Finite Element Method, and the initial one is integrated in time by the difference predictor-corrector method. Two forms are given for the equation of state describing the radiation swelling strains: first is for the components of the strain tensor as well as second is prepared for their rates. The hypothesis about the linear correspondence of the received radiation dose and the deformation time, during which radiation swelling strains develop, are analyzed. A number of questions that require answers when using equations with a complex stress state in which the radiation swelling strains are directly depend on stresses, are discussed. Based on the processing of experimental data on the swelling of tubes made of steel 316Ti in the temperature range of 450-460 °С, a form of the equation for the radiation swelling strain rate is proposed, and the constants included in it are determined. Using the example of numerical modelling of the deformation of tubes were made of steel 316Ti and loaded by inner pressure, the applicability of the classical approach for the analysis of the stress-strain state in the presence of radiation swelling strains is shown.

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Virta, Jari, Simo Koponen und Ilmari Absetz. „Measurement of swelling stresses in spruce (Picea abies) samples“. Building and Environment 41, Nr. 8 (August 2006): 1014–18. http://dx.doi.org/10.1016/j.buildenv.2005.10.012.

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Dissertationen zum Thema "Swelling stresses"

Panek, Joel C. „Fragmentation of brittle polymeric toner line caused by swelling of paper substrate during immersion in water“. Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/5808.

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Vosgien, Lacombre Coralie. „Influence du taux de pigment sur la dégradation de revêtements polymères anticorrosion sous contraintes environnementales couplées“. Thesis, La Rochelle, 2017. http://www.theses.fr/2017LAROS002/document.

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Cette étude se focalise sur l’influence du dioxyde de titane sur le comportement d’une résine polymère époxy modèle. Les systèmes considérés sont des composites constitués d’un pigment, le dioxyde de titane TiO2 à des taux massiques de 10% et 20%, et de résine DGEBA-DAMP. Tout d’abord, les propriétés mécaniques et thermiques de films libres complètement réticulés sont mesurées par DSC et DMA. Les résultats des composites sont comparés à ceux de la résine pure pour mieux comprendre l’impact du TiO2. Les films libres de composites sont ensuite immergés dans de l’eau pure à différentes températures (30, 40, 50 et 60 °C) pour étudier la prise en eau et les coefficients de diffusion par gravimétrie. L’évolution des propriétés de nos systèmes est aussi étudiée pour avoir accès à l’influence de l’eau sur leur comportement. Dans un second temps, les composites sont réticulés sur des plaques d’acier et certaines sont soumises à des contraintes mécaniques externes. Ces revêtements sont alors plongés dans une solution saline et l’absorption d’eau est suivie par SIE. Une dernière étape de ce travail consiste à suivre le gonflement des revêtements composites par SECM. Finalement, la comparaison des résultats de la résine pure et des composites obtenus pour les films libres et les revêtements permet de mettre en avant l’impact du TiO2 sur la durabilité de ces systèmes, essentiellement dû au développement de contraintes internes
This study focuses on the influence of titanium dioxide on the behavior of a model epoxy polymer resin. The considered systems are composites which contain titanium dioxide TiO2 as pigment and DGEBA-DAMP as epoxy resin. The studied amounts of titanium dioxide are 10 wt.% and 20 wt.%. Firstly, mechanical and thermal properties of totally cured free films are studied by DSC and DMA. The results of the composites are compared to those of the resin alone to better understand the impact of the titanium dioxide. Then, composite free films are immersed in pure water at different temperatures (30, 40, 50 and 60 °C) to investigate water uptake and diffusion coefficients by gravimetry. At each step of ageing, measurements of the properties are carried out to show the influence of water on our systems behaviors. Then, composites of epoxy resin and pigment are applied on steel panels and some samples are submitted to external mechanical stresses. These coatings are submitted to an environment of NaCl 3 wt.% saline solution and water uptake is followed by Electrochemical Impedance Spectroscopy (EIS). Swelling of composites coatings is followed by SECM in a last step of this work. Finally, a comparison of the results of pure resin and of composite gives access to the impact of titanium dioxide on the durability of these systems. It is mainly due to the presence of internal stresses

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Augustine, Anusree. „Swelling induced debonding of thin hydrogel films grafted on silicon substrate : the role of interface physical-chemistry“. Electronic Thesis or Diss., Université Paris sciences et lettres, 2022. http://www.theses.fr/2022UPSLS040.

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Les revêtements d'hydrogel sont des réseaux de polymères transparents et hydrophiles capables d’abosrber plusieurs fois leur épaisseur en eau. Cependant, les contraintes induites par le gonflement du film peuvent entraîner un décollement préjudiciable de l'hydrogel ce qui peut limiter l’utilisation pratique des ces revêtements. Dans cette étude, nous proposons de décrire les mécanismes de décollement de films minces d’hydrogel en fonction de leur densité de greffage à l'interface film/substrat. Le but est de pouvoir contrôler et prédire la dégradation des revêtements hydrogel pendant le gonflement ou sous des contraintes de contact. Dans ce but, nous avons développé une méthodologie permettant de mesurer l'initiation et la propagation de la délamination induite par le gonflement de films minces d’hydrogel à partir de défauts d'interface préexistants bien contrôlés.Des films minces d'hydrogel de poly(diméthylacrylamide) (PDMA) attachés à la surface sont préparés sur des plaquettes de silicium à partir de la réticulation et du greffage simultanés (CLAG) de chaînes polymères fonctionnalisées par la chimie click thiol-ène. Cette stratégie permet de faire varier l'épaisseur du film (0.1 - 2 µm) et de contrôler le taux de gonflement du réseau, ici fixé à 2, tout en assurant une densité de réticulation homogène. Afin de faire varier la résistance de l'interface film/substrat, le substrat en silicium est greffé avec des mélanges de mercaptosilane (réactif) et de propylsilane (inerte) dans différentes proportions avant le dépôt du film mince. Alors que le mercaptosilane est capable de former des liaisons covalentes avec le réseau PDMA, le propylsilane ne réagit pas, ce qui permet de contrôler le taux de greffage du film mince d’hydrogel sur le substrat. Nous caractérisons la fraction de surface de mercaptosilane ainsi obtenue par des analyses XPS et TOF-SIMS. Par ailleurs, toujours à l’interface subtrat/film, des défauts linéaires bien contrôlés ayant une faible adhérence (largeur entre 10 et 100 µm) sont créés sur le substrat en passivant de façon localisée les groupes thiol réactifs par microlithographie. Ces défauts nucléent le décollement des films de façon bien localisée, ce qui permet ensuite de suivre la propagation de la décohésion à partir de ces défauts.Le décollement du film induit par le gonflement est réalisé sous un flux de vapeur constant assurant la saturation du film en eau. En observant le décollement progressif du film à partir des défauts linéaires préexistants, nous retrouvons un motif d’instabilité classique dit de fil de téléphone et nous montrons que le décollement résulte de contraintes de gonflement localisées proche de la ligne de décollement. Nous mesurons la vitesse de propagation du décollement dans la zone où le film est greffé sur le substrat et nous observons qu’elle augmente de deux ordres de grandeur lorsque la quantité de propylsilane dans le mélange de silanes réactifs passe de 0 à 90 %, c’est-à-dire lorsque le taux de greffage du film décroit. Un seuil d'épaisseur pour le décollement est également observé, les films pouvant se décoller étant d’autant plus minces que le taux de greffage du film ets faible. Les mesures de ce seuil sont discutées à partir d'un argument simple de mécanique de la rupture qui permet de rendre compte semi quantitativement de nos mesures
Hydrogel coatings are transparent and hydrophilic polymer networks that absorb a lot of water and can be suitable candidates for anti-mist coatings. However, swelling-induced stresses within the film can result in detrimental debonding of hydrogel and may fail. In this study, these debonding processes are investigated in the relation to the grafting density at the film/substrate interface, so as to control and predict the failure of the coatings during swelling or under contact stresses. For that purpose, we have developed a methodology consisting in monitoring the initiation and the propagation of swelling-induced delamination from well-controlled preexisting interface defects.Surface-attached poly(dimethylacrylamide) (PDMA) hydrogel thin films are prepared on silicon wafers from the simultaneous Cross-Linking And Grafting (CLAG) of functionalized polymer chains by thiol-ene click chemistry. This strategy allows to tune the film thickness (0.1-2 µm) while ensuring a homogeneous crosslinking density. In order to vary the strength of the film/substrate interface, the silicon wafer is grafted by mixing reactive mercaptosilane and unreactive propylsilane in various proportions prior to the formation of the hydrogel film. We characterize the mercaptosilane surface fraction thus obtained by XPS and TOF-SIMS analyses. Well-controlled line defects (width between 2 and 100 µm) are also created to nucleate delamination of the hydrogel from the substrate.Swelling-induced debonding of the film is achieved under a constant vapor flow ensuring water saturation. Optical observations show the progressive debonding of the film from the pre-existing line defects under the action of localized swelling stresses. We obtain a delamination pattern of typical so-called telephone cord instability. We measure the debonding propagation velocity where the hydrogel is grafted to the substrate. The debonding rate is found to decrease over two orders of magnitude when the amount of mercaptosilane in the reactive silane mixture is increased from 10% to 100% while increasing the covalent bonds between hydrogel and substrate. A threshold thickness for debonding is also observed. This threshold thickness increases with the amount of mercaptosilane used to graft the substrate. We derived quantitative values of the interface fracture energy from the measured thickness threshold with a simple fracture mechanics model

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Giambastiani, Mauricio. „Comportamento dependente do tempo de rochas sulfáticas de anidrita e gipso“. Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/18/18132/tde-18042006-112853/.

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A presente tese tem por objetivo contribuir para o conhecimento do comportamento dependente do tempo das rochas de anidrita e gipso. O maior interesse é fornecer argumentos convincentes sobre os mecanismos físicos responsáveis pelas deformações lentas observadas em algumas escavações subterrâneas realizadas em maciços dessas rochas na Europa, aspecto este que hoje está bastante confuso e escassamente estudado. A hipótese central desta pesquisa é que o comportamento dependente do tempo das rochas de anidrita e gipso deve-se parcial e/ou totalmente às propriedades reológicas (fluência) e não exclusivamente a expansão decorrente da transformação anidrita gipso como a maioria dos autores sustenta. Este problema será analisado a partir de uma perspectiva experimental através de ensaios específicos. Os ensaios de expansão axial livre em rochas de anidrita permitiram concluir que quando submersas em água destilada, experimentam diminuição de volume por dissolução. Já as amostras de anidrita em contato com solução saturada em 'CA'SO IND.4' mostram uma relação não linear entre deformação axial e o tempo indicando uma taxa de expansão que decresce com o tempo. As taxas de expansão axial variam entre 0,3 e 2,4%/ano. A novidade é que esta expansão se deve à deposição de uma camada contínua formada por neocristais de gipso e não a expansão por hidratação da anidrita como acontece com os argilominerais. O mecanismo de transformação consiste na dissolução da anidrita e posterior precipitação do gipso em condições de sobre-saturação da solução. A transformação mineralógica acontece, na natureza, em condições propícias de temperatura e saturação da solução com íons 'CA POT.2+' e 'SO IND.4'POT.2-'. Propõe-se uma teoria alternativa sobre deformações lentas de maciços sulfáticos baseada na força de cristalização decorrente da deposição de cristais de gipso nas juntas do maciço rochoso. Propõe-se utilizar as formulações termodinâmicas propostas para expansão de concretos por crescimento de etringita e gipso. Os ensaios de fluência uniaxial sob compressão axial constante mostram que ambos os tipos de rochas sulfáticas apresentam comportamentos elasto-visco-plásticos e taxas de deformação axial e lateral da ordem de '10 POT.-12' a '10 POT.-10' 'S POT.-1'. A deflagração da fluência secundária acontece sob tensões de 4 6 MPa para gipsitas e de 25 40 MPa para anidritas. As análises sobre os possíveis mecanismos de deformação por fluência foram inconsistentes e nenhuma conclusão definitiva foi atingida. Aparentemente a baixas tensões atuariam mecanismos de difusão e dissolução por pressão. A tensões intermediárias dominariam mecanismos de deslocamentos intra e intercristalinos e a altas tensões as rochas deformariam por propagação de microfissuramento. Ensaios de fluência acoplados a sensores de emissão acústica mostram a manifestação de eventos microssísmicos que usualmente se atribuem à propagação de microfraturas mas que podem dever-se a outros mecanismos. Tanto as taxas de expansão axial como de fluência são compatíveis com as taxas de convergência medidas em algumas obras subterrâneas escavadas em maciços sulfáticos, verificando a hipótese central da pesquisa
The purpose of this thesis is to contribute for the knowledge of time-dependent behavior of sulfatic rocks of anhydrite and gypsum. Emphasis is given to provide straightforward arguments about physical mechanisms responsible for creep observed in some underground excavations in those rocks in Europe. Explanation for this phenomena is not clear yet and studies about them are still scarce. The backbone idea behind this research is that the time-dependent behavior of anhydrite and gypsum is totally or at least partially due to rheological properties, and not exclusively due to swelling resulting from the anhydritegypsum transformation. This problem was investigated experimentally with specific tests. Free swelling tests on anhydrite led to the conclusion that when immersed into distilled water, volume decrease due to dissolution is observed. Anhydrite samples in contact with a saturated solution of 'CA'SO IND.4' present a nonlinear relationship between axial strain and time, indicating swelling rate decreasing with time. Axial swelling rates vary between 0,3% and 2,4%/year. The new concept is that this swelling is due to the deposition of a continuous layer of gypsum composed by gypsum neo-crystals, and not due to hydration swelling of anhydrite, a usual with clay minerals. The transformation mechanism consists of anhydrite dissolution and later precipitation of gypsum under over-saturation condition of the solution. The mineralogical transformation takes place in nature under favorable conditions of temperature and solution saturation with 'CA POT.2+' and 'SO IND.4'POT.2-' ions. An alternative theory is proposed about creep of sulfatic rock masses based on crystallization forces resulting from the deposition of gypsum crystals in the rock masses joints. The use of thermodynamic formulations is proposed for concrete swelling due to the growth of ettringite and gypsum. Uniaxial compression creep tests show that both types of sulfatic rocks present elasto-visco-plastic behavior and axial and lateral strain rates of the order of '10 POT.-12' to '10 POT.-10' 'S POT.-1'. Triggering of secondary creep takes places under stresses of the order of 4 6 MPa for gypsum and 25 40 MPa for anhydrite. The analyses about the possible creep mechanisms were not consistent and no definite conclusion has been reached get. Apparently under low stresses diffusion and pressure dissolution mechanism dominate. Under intermediate stresses, intra- and inter crystalline displacement mechanisms seem to dominate, and under high stresses rock deform due to microcrack propagation. Creep tests monitored with acoustic emission devices show the occurrence of microseismic events attributed to microcrack propagation. Both axial swelling and creep rock are compatible with convergence rocks measured in some underground works excavated in sulfatic rock masses, following the central idea of this thesis

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BARLA, MARCO. „Tunnels in swelling ground: simulation of 3D stress paths by triaxial laboratory testing“. Doctoral thesis, Politecnico di Torino, 1999. http://hdl.handle.net/11583/2504404.

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The research is devoted to study the swelling behaviour in tunnels. A new triaxial testing procedure is developed, which is able to quantify the swelling behaviour of soft rocks and stiff soils. The Caneva Clay is tested both by conventional oedometer swelling tests and by the new triaxial test. The swelling parameters of the clay are quantified for predictive analyses of the swelling behaviour at the tunnel scale.

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Armstrong, Michelle Hine, Tepole Adrián Buganza, Ellen Kuhl, Bruce R. Simon und Geest Jonathan P. Vande. „A Finite Element Model for Mixed Porohyperelasticity with Transport, Swelling, and Growth“. Public Library of Science, 2016. http://hdl.handle.net/10150/614631.

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The purpose of this manuscript is to establish a unified theory of porohyperelasticity with transport and growth and to demonstrate the capability of this theory using a finite element model developed in MATLAB. We combine the theories of volumetric growth and mixed porohyperelasticity with transport and swelling (MPHETS) to derive a new method that models growth of biological soft tissues. The conservation equations and constitutive equations are developed for both solid-only growth and solid/fluid growth. An axisymmetric finite element framework is introduced for the new theory of growing MPHETS (GMPHETS). To illustrate the capabilities of this model, several example finite element test problems are considered using model geometry and material parameters based on experimental data from a porcine coronary artery. Multiple growth laws are considered, including time-driven, concentrationdriven, and stress-driven growth. Time-driven growth is compared against an exact analytical solution to validate the model. For concentration-dependent growth, changing the diffusivity (representing a change in drug) fundamentally changes growth behavior. We further demonstrate that for stress-dependent, solid-only growth of an artery, growth of an MPHETS model results in a more uniform hoop stress than growth in a hyperelastic model for the same amount of growth time using the same growth law. This may have implications in the context of developing residual stresses in soft tissues under intraluminal pressure. To our knowledge, this manuscript provides the first full description of an MPHETS model with growth. The developed computational framework can be used in concert with novel in-vitro and in-vivo experimental approaches to identify the governing growth laws for various soft tissues.

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Cesaretti, Juan Manuel. „Mechanical stress and stress compensation in Hall sensors“. Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/28202.

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Lobosco, Vinicius. „On the Modelling of Mechanical Dewatering in Papermaking“. Doctoral thesis, KTH, Fibre and Polymer Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3702.

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Most of the water fed into a paper machine is removedmechanically in the forming and press sections. One of thefactor which has an important influence on mechanicaldewatering, i.e. in both forming and pressing, is thestress-strain behaviour of the fibre network.

The focus of this thesis is on the development of improvedmathematical descriptions of the stress-strain behaviourexhibited by fibre networks in the forming and press sections.The first part of the thesis presents a physically based modelof the forming and densification of fibre mats in twin-wireformers. The model can calculate the ecect of the applicationof a varied load through the forming section. It was developedfrom mass and momentum balances of the fibre and liquid phases,the fibre mat stress-porosity relation and an expression forthe permeability as a function of the porosity. The fibre-matstress-porosity relation used is rate-independent and presentshysteresis. Simulations have been conducted to study theeffects of roll pressure, blade pulses, wire tension andbeating. The effect of sequential blade pressure pulses afterthe forming roll on the dewatering and the concentrationgradients could be characterised. The simulations alsoexhibited rewetting by expansion when the fibre mats left theforming roll. Increasing wire tension resulted in increaseddewatering, but the rate of increase diminished rapidly withincreasing tension. The simulation results also indicated thatbeating has a large influence on dewatering.

The second part of the thesis presents two models of therate-dependent stress-strain behaviour of the fibre networkthat is observed in wet pressing. The first model was based onthe approach pioneered by Perzyna (1966) for strain-ratedependent plasticity and was quite satisfactory for calculatingthe stress-strain behaviour of the fibre network in singlepress nips. It was successfully applied for studyingdensification and dewatering in both normal wet pressing andhigh temperature wet pressing. However, the first model onlyincludes rate dependence in the compression phase of thecompressionexpansion cycle; the expansion phase is treated asbeing rate independent

The second model of the stress-strain behaviour of the fibrenetwork treats both compression and expansion as being ratedependent, according to experimental observations. It is basedon the idea that the wet fibre web may be conceived as alayered network of restricted swelling gels. A swollen fibre isa restricted gel, the inner swelling pressure in a swollenfibre wall being balanced by the stresses in the fibre wallstructure. The observed rate dependence of wet webs in bothcompression and expansion phases was attributed to the flow ofwater out of and into the fibre walls. The second model gavepredictions that are in good agreement with results fromuniaxial experiments using pressure pulses of arbitrary shapefor both a single pulse and a sequence of pulses. It maytherefore be used as a general model for the rheologicalbehaviour of the wet fibre network in wet pressing, providedthe model parameters are estimated from experimental data withsmall experimental error.

KEYWORDS:Paper, modelling, dewatering, forming, wetpressing, fibre network stress, rheology, hysteresis,intra-fibre water, compressibility, structural stress,stress-strain, restricted gels, swelling.

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Stamatialis, Dimitrios F., Dimitrios N. Soulas und Merope Sanopouloua. „Mechanisms of non-fickian micromolecular diffusion in glassy polymer films: analysis of experimental sorption and concurrent dilation kinetics in the light of a differential swelling stress model“. Diffusion fundamentals 11 (2009) 10, S. 1-2, 2009. https://ul.qucosa.de/id/qucosa%3A13930.

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Philip, Benjamin N. „Characterization and physiological role of aquaporins during desiccation and freezing in Eurosta solidaginis“. Miami University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=miami1280843234.

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Bücher zum Thema "Swelling stresses"

Grant, Sophie. Genius Foods: The Balance of Contrast in the Kitchen. Diabetes, Swelling, Biliary Calculations, Anti-Inflammatory Diet, Weight and Fat Liver Problems. Stress Free Meals to Heal the Immune System. Independently Published, 2020.

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Buchteile zum Thema "Swelling stresses"

Wittke, Walter. „Consideration of Stresses and Deformations due to Swelling in Finite Element Analyses“. In Rock Mechanics, 318–22. Berlin, Heidelberg: Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-88109-1_7.

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Neu, Gerrit Emanuel, Florian Christ, Tagir Iskhakov, Christina Krikelis, Diego Nicolás Petraroia, Sven Plückelmann, Maximilian Schoen et al. „Tunnel Linings“. In Interaction Modeling in Mechanized Tunneling, 253–327. Cham: Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-24066-9_5.

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AbstractIn this chapter, important research results for the development of a robust and damage-tolerant multimaterial tunnel lining are presented. This includes the production, design and optimization of fiber-reinforced hybrid segmental lining systems based on numerical models and experimental investigations under tunneling loads. In addition, novel tail void grouting materials are developed and optimized regarding their infiltration and hardening behavior while taking the interaction with the surrounding ground into account. In order to expand the applicability of mechanized tunneling regarding soils characterized by significant swelling potential due to water uptake by clay minerals, a deformable segmental lining system is presented. The risk of damage due to high localized loads is reduced by the integration of additional radial protective layers on the lining segments and a compressible annular gap grout, which protect the tunnel structure by undergoing high deformations after reaching a certain yielding load. However, the deformability of such support systems affects the distribution of the stresses around the tunnel which governs the magnitude and buildup of the swelling pressure in the soil. Therefore, the development of damage tolerant lining systems requires a material and structural design which ensures an optimal soil-structure interaction through a synergy of computational and experimental techniques.

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Plaas, Anna H. K., Meghan M. Moran, John D. Sandy und Vincent C. Hascall. „Aggrecan and Hyaluronan: The Infamous Cartilage Polyelectrolytes – Then and Now“. In Advances in Experimental Medicine and Biology, 3–29. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-25588-5_1.

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AbstractCartilages are unique in the family of connective tissues in that they contain a high concentration of the glycosaminoglycans, chondroitinsulfate and keratan sulfate attached to the core protein of the proteoglycan, aggrecan. Multiple aggrecan molecules are organized in the extracellular matrix via a domain-specific molecular interaction with hyaluronan and a link protein, and these high molecular weight aggregates are immobilized within the collagen and glycoproteinnetwork. The high negative charge density of glycosaminoglycans provides hydrophilicity, high osmotic swelling pressure and conformational flexibility, which together function to absorb fluctuations in biomechanical stresses on cartilage during movement of an articular joint. We have summarized information on the history and current knowledge obtained by biochemical and genetic approaches, on cell-mediated regulation of aggrecan metabolism and its role in skeletal development, growth as well as during the development of joint disease. In addition, we describe the pathways for hyaluronan metabolism, with particular focus on the role as a “metabolicrheostat” during chondrocyte responses in cartilage remodeling in growth and disease.Future advances in effective therapeutic targeting of cartilage loss during osteoarthritic diseases of the joint as an organ as well as in cartilage tissue engineering would benefit from ‘big data’ approaches and bioinformatics, to uncover novel feed-forward and feed-back mechanisms for regulating transcription and translation of genes and their integration into cell-specific pathways.

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Boersma, L., Yongsheng Feng und Xiaomei Li. „Osmotic Adjustment in Plant Cells Exposed to Drought and Temperature Stress: Can a Cause and Effect Hypothesis be Formulated and Tested?“ In Mechanics of Swelling, 143–64. Berlin, Heidelberg: Springer Berlin Heidelberg, 1992. http://dx.doi.org/10.1007/978-3-642-84619-9_6.

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Kolditz, Olaf, Tuanny Cajuhi, Ralf-Michael Günther, Holger Steeb, Frank Wuttke, Keita Yoshioka, Norbert Grunwald und Thomas Nagel. „Synthesis and Outlook“. In SpringerBriefs in Earth System Sciences, 91–98. Cham: Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-26493-1_6.

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AbstractThe principal interest of the GeomInt project consists of the investigation of effects on barrier integrity of three host rock formations: clay, salt and crystalline. The project focuses on distinct physical processes that can influence barrier integrity in these rocks, particularly those related to swelling and shrinkage, pressure-driven percolation and stress redistribution.

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Kolditz, Olaf, Uwe-Jens Görke, Heinz Konietzky, Jobst Maßmann, Mathias Nest, Holger Steeb, Frank Wuttke und Thomas Nagel. „Synthesis and Outlook“. In GeomInt–Mechanical Integrity of Host Rocks, 227–42. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-61909-1_6.

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AbstractAs a result of the GeomInt research project (Chap. 1) a broad combined experimental and numerical platform for the investigation of discontinuities due to swelling and shrinking processes (WP1, Sect. 2.3), pressure-driven percolation (WP2, Sect. 2.4) and stress redistribution (WP3, Sect. 2.4) for important reservoir and barrier rocks (clay, salt, crystalline) has been developed. Model comparisons for damage and fracture processes driven by different processes provide information on the optimal areas of application of the numerical methods (Sect. 2.5).

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Setton, Lori A., Weiyong Gu, W. Michael Lai und Van C. Mow. „Predictions of the Swelling-Induced Pre-Stress in Articular Cartilage“. In Solid Mechanics and Its Applications, 299–320. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-015-8698-6_17.

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Grimal, Etienne. „Contribution of Stress Measurements in Modelling Structures Affected by Concrete Swelling“. In RILEM Bookseries, 392–99. Cham: Springer Nature Switzerland, 2024. http://dx.doi.org/10.1007/978-3-031-59349-9_45.

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Li, Sheng-Jie, Chao-Sheng Tang, Zhi-Guo Chen, Dong-Wei Wang, Bin Shi und Inyang Hilary. „Influence of Stress-Strain Boundary Conditions on the Swelling Behavior of Bentonite“. In Proceedings of GeoShanghai 2018 International Conference: Fundamentals of Soil Behaviours, 679–88. Singapore: Springer Singapore, 2018. http://dx.doi.org/10.1007/978-981-13-0125-4_76.

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Kuhara, Kei, und Manabu Enoki. „Stress Analysis of the Swelling and Deswelling Process of Thermo-Responsive Gel“. In Key Engineering Materials, 2215–18. Stafa: Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/0-87849-456-1.2215.

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Konferenzberichte zum Thema "Swelling stresses"

Stellrecht, Eric, Bongtae Han und Michael Pecht. „Measurement of Hygroscopic Swelling in Mold Compounds and Its Effect on PEM Reliability“. In ASME 2003 International Electronic Packaging Technical Conference and Exhibition. ASMEDC, 2003. http://dx.doi.org/10.1115/ipack2003-35252.

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Hygroscopic stresses arise in a plastic encapsulated microcircuit (PEM) when the mold compound swells upon absorbing moisture and the lead frame, die paddle, and silicon die, do not experience swelling. Similar to the thermal stress produced by the mismatch of coefficients of thermal expansion between adjacent materials, the hygroscopic stress increases as the hygroscopic swelling coefficient of the mold compound increases. Accurate measurement of hygroscopic swelling is essential in assessing the effect of hygroscopic stresses on package reliability. In this paper, a whole-field experimental method to characterize the hygroscopic swelling of mold compounds is proposed. The method is implemented to determine the hygroscopic swelling and the corresponding coefficient of hygroscopic contraction of five commercial molding compounds. A comparison between the hygroscopic and thermally induced mismatch strains in PEMs is presented and its implication on PEMs reliability is discussed.

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Liu, Z. P., W. Y. Gu, W. M. Lai und V. C. Mow. „Analysis of One-Dimensional Confined Swelling of Charged-Hydrated Soft Tissues“. In ASME 1997 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/imece1997-0289.

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Abstract Charged hydrated soft tissues such as articular cartilage and the intervertebral disc have a strong tendency to swell in a hypotonic bath because of the high fixed charge density (FCD) within the tissue [e.g., 1–4]. For an excised tissue without externally applied loads, the tissue volume will change in response to changes in a bathing solution (free swelling) until the osmotic pressure is balanced by the elastic stresses on the solid matrix. A mechanical stress is needed to prevent the tissue from swelling from a given reference state (e.g., 0.15M NaCl). This stress may be called the swelling pressure relative to this reference state. The kinetic response of the swelling pressure to changes in bathing solution is associated with tissue material properties, such as the FCD, hydraulic permeability, ion diffusivity and stiffness of the solid matrix. In this study, we report our analysis on the one-dimensional confined swelling experiment of a charged hydrated soft tissue using the mechano-electrochemical theory developed in [3].

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Han, B., E. Stellrecht und M. Pecht. „Effect of Hygroscopic Swelling of Mold Compound on PEM Reliability“. In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-42223.

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Polymeric mold compounds absorb moisture, and thus swell, when exposed to a humid environment [1]. Hygroscopic stresses arise in plastic encapsulated microcircuits (PEMs) when the mold compound swells upon absorbing moisture and the lead frame, die paddle, and semiconductor chip, do not experience swelling.

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Kaneshima, Takuma, Fuqiao Bai und Nobuo Morita. „Comprehensive Analysis of Borehole Stability with Temperature, Swelling, and Pore Pressure Change for Layered and Orthotropic Formations“. In SPE/IADC International Drilling Conference and Exhibition. SPE, 2021. http://dx.doi.org/10.2118/204068-ms.

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Abstract Borehole stability depends on various parameters such as rock strength, rock deformations, in-situ stress, borehole trajectory, shale swelling, pore pressure change due to osmosis, overbalance mud weight and temperature. The objective of this work is to construct analytical and numerical equations to predict borehole failure including all these parameters, and to comprehensively propose a methodology to improve the borehole stability. Analytical solutions are developed for inclined wells with respect to in-situ stress, shale swelling, pore pressure change due to osmosis, overbalance mud weight and temperature. A numerical model is developed for 3D inclined wells with orthotropic formation and layered formation. Using the analytical and the numerical models, stress state around inclined wells are evaluated. The breakout angle is predicted based on Mohr-Coulomb, Mogi, Lade and Drucker-Prager failure theories. Polar diagrams of mud weights are compared to judge the effect of each parameter and the magnitude predicted by the different failure theories. Shale swelling and pore pressure change due to osmosis are the most difficult to estimate among above-mentioned parameters. The laboratory measured swelling of cores obtained from various formations showed that the magnitude to induce breakouts caused by swelling was the largest comparing with other parameters. Therefore, when shale stability problems occur, we need to estimate the magnitude of shale swelling and osmosis due to water potential difference. Then, to overcome the shale stability problem, we evaluated the sensitivity of human controllable parameters on borehole stability. The parameters which can be controlled by drilling engineers are overbalance, type of mud, borehole temperature and borehole trajectory. If the shale swelling is small, the borehole stability is improved by the mud weight. However, from the swelling tests from the cores of Nankai-Trough, we estimated unless we used a swelling inhibitor to reduce the swelling less than 0.1%, the well was not possible to drill through. Actually, the well was abandoned due to instability after trying side track several times. Unlike previous works, this paper uses all important parameters (swelling, temperature, pore pressure, orthotropic formation, layered formation) to estimate the stresses around inclined wells with the same formation conditions for quantitative analysis. Failure analysis include Mohr, Mogi, Lade and Drucker-Prager. Finally, the polar diagrams of critical mud weight are used to judge whether we can choose well trajectory, orientation with respect to bedding planes, mud weight, shale inhibitor, and temperature to stabilize the borehole.

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Williams, J. R., R. N. Natarajan und G. B. J. Andersson. „Prediction of Endplate Bulging With and Without Inclusion of Physiological Swelling Pressure and Strain Dependent Permeability and Porosity“. In ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-59409.

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Finite element models were used to understand how changes in physiological factors such as swelling pressure and strain dependent permeability alters the biomechanical characteristics of lumbar discs under compressive loads. Exclusion of these physiological factors increased endplate stresses, reduced endplate bulge and reduced nucleus and annulus stresses.

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Ozaltun, Hakan, Herman Shen und Pavel Medvedev. „Numerical Simulation for Mechanical Behavior of U10Mo Monolithic Miniplates for Research and Test Reactors“. In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-62114.

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This article presents assessment of the mechanical behavior of U-10wt% Mo (U10Mo) alloy based monolithic fuel plates subject to irradiation. Monolithic, plate-type fuel is a new fuel form being developed for research and test reactors to achieve higher uranium densities within the reactor core to allow the use of low-enriched uranium fuel in high-performance reactors. Identification of the stress/strain characteristics is important for understanding the in-reactor performance of these plate-type fuels. For this work, three distinct cases were considered: (1) fabrication induced residual stresses (2) thermal cycling of fabricated plates; and finally (3) transient mechanical behavior under actual operating conditions. Because the temperatures approach the melting temperature of the cladding during the fabrication and thermal cycling, high temperature material properties were incorporated to improve the accuracy. Once residual stress fields due to fabrication process were identified, solution was used as initial state for the subsequent simulations. For thermal cycling simulation, elasto-plastic material model with thermal creep was constructed and residual stresses caused by the fabrication process were included. For in-service simulation, coupled fluid-thermal-structural interaction was considered. First, temperature field on the plates was calculated and this field was used to compute the thermal stresses. For time dependent mechanical behavior, thermal creep of cladding, volumetric swelling and fission induced creep of the fuel foil were considered. The analysis showed that the stresses evolve very rapidly in the reactor. While swelling of the foil increases the stress of the foil, irradiation induced creep causes stress relaxation.

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Carrilho, Leo A. „Stress Analysis of the Pressurized-Water Reactor Control Rod Under Operating Conditions“. In 2020 International Conference on Nuclear Engineering collocated with the ASME 2020 Power Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/icone2020-16872.

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Abstract This work aims to develop a finite element model of a PWR control rod at operating conditions for stress analysis of the rod cladding. The finite element model simulates a control rod exposed to high operating temperatures and pressure while portions of the rod are irradiated, resulting in accumulated fluence of neutrons by the rod materials. These high temperature and accumulated fluence induce thermal expansion and swelling of the rod materials, especially of the absorber, which may eventually interact with the rod cladding, generating stresses and strains in the wall of the cladding tube. Moreover, if the maximum stress or strain in the tube wall exceeds the design allowable limit, the absorber rod is considered failed. The author creates the control rod finite element model and apply the operating loads on two-dimensional axisymmetric elements to obtain displacements, temperatures, stresses, and strains. The model also includes contact surface elements to evaluate eventual mechanical interactions between absorber and cladding due to thermal expansion and swelling effects. This is a coupled nonlinear static analysis solution that includes thermal expansion effects to calculate temperature distribution and subsequent thermal strains in the absorber rod due to the heat generation rates and coolant temperature; swelling analysis to calculate absorber growth induced by irradiation; and creep analysis to calculate absorber stress relaxation under coolant pressure and temperature. The finite element model is capable of determining whether or not absorber-to-cladding gap closure will occur and if so, calculate maximum stress and strain in the rod cladding associated with mechanical interaction between the two components induced by the operating temperature and thermal fluence loads.

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Tang, Changbing, Yongjun Jiao, Wenjie Li, Tao Qing, Yifei Miao und Ping Chen. „Numerical Simulation of Different Sizes Missing Pellet Surface Effects on Thermal-Mechanical Behaviors in Nuclear Fuel Rods“. In 2016 24th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/icone24-60116.

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Nuclear fuel rods is mainly composed of uranium dioxide pellets and zirconium alloy cladding, there is a gap between pellets and cladding, which is filled with helium. Under the reactor operation conditions, pellets produce a lot of heat by nuclear fission reactions and at the same time also produce lots of radioactive fission products. Cladding serve as the first barrier to accommodate radioactive fission product, needs to maintain its structural integrity under the reactor operation conditions. Cladding stresses can be effectively limited by controlling power increase rates. However, pellet manufacturing defects such as missing pellet surface (MPS), may lead to cladding local stress significantly high to cause cladding failure. Simulating the impact of these defects correctly can help prevent these types of failure. MPS defects are 3D phenomenon, needs 3D modeling method to study the influence of these defects on the cladding .In this paper, stress update algorithm is derived, with the help of ABAQUS (a commercial finite element software), simulated the thermal-mechanical behaviors of the MPS defects fuel rod with a 3D FEM and completed the sensitivity analysis of MPS defects size for the fuel performance. The models included in this simulation, including pellet irradiation swelling (fission gas products induced swelling and fission solid products induced swelling), pellet densification, pellet relocation, pellet thermal expansion, pellet irradiation creep, pellet irradiation hardening, cladding irradiation growth, cladding thermal expansion, cladding thermal creep, cladding irradiation creep, cladding irradiation hardening and gap heat transfer (gas heat conduction, radiation heat transfer and contact heat conduction) etc. Furthermore, considering the effects of irradiation and temperature on the material parameters such as thermal conductivity, specific heat and young’s modulus etc. According to the simulation result, showing that MPS defects have a large impact on the performance of fuel rods, this impact will be more obvious with the size of MPS defects increase. The MPS defects cause larger gap distance between pellet and cladding, higher gap distance causes smaller gap conductance, and then causes elevated temperature at the center of the pellet and in the region of the pellet adjacent to the defect. The cladding temperature is reduced in the area immediately across from the defect, and is elevated in neighboring areas. Meanwhile, MPS defects clearly have a significant effect on stress distribution and maximum stress of the cladding, cause high tensile stresses in the inner surface of the cladding and high compressive stresses on the outer surface of the cladding at the center of the defect. Around the boundaries of the defect, the stresses are reversed, with high compressive stresses on the cladding interior and high tensile stresses on the cladding exterior.

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Chahine, Nadeen O., Christopher C. B. Wang, Clark T. Hung und Gerard A. Ateshian. „Determination of Poisson’s Ratios of Bovine Articular Cartilage in Tension and Compression Using Osmotic and Mechanical Loading“. In ASME 2002 International Mechanical Engineering Congress and Exposition. ASMEDC, 2002. http://dx.doi.org/10.1115/imece2002-32622.

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The existence of osmotic pressure inside cartilage gives the tissue a propensity to swell. This swelling pressure is balanced by the tensile stresses generated within the solid matrix at free-swelling [1, 2]. Recent studies have shown that cartilage exhibits significant strain-softening when compressed relative to its free-swelling state [3–5]. Such strain-softening behavior has been physically interpreted within the context of osmotic swelling pressure and tension-compression nonlinearity [4, 9]. This has provided the rationale for extracting both the tensile and compressive Young’s moduli from uniaxial compression tests on the same specimen [4, 5]. The goal of the current study is to optically determine another important elastic property, i.e. the equilibrium Poisson’s ratio of young bovine articular cartilage when uniaxially compressed along its three characteristic directions: parallel and perpendicular to the split-line direction (1- and 2-direction, respectively), and in a direction normal to the articular surface (3-direction). Furthermore, the external bath concentration effects on the Poisson’s ratios will be explored at various strain levels.

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Holck, O., J. Bauer, T. Braun, H. Walter, O. Wittler, B. Wunderle und K. D. Lang. „Moisture transport and swelling stresses at moulding-compound substrate interfaces investigated by molecular modeling and finite element simulations“. In 2013 14th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE). IEEE, 2013. http://dx.doi.org/10.1109/eurosime.2013.6529958.

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Berichte der Organisationen zum Thema "Swelling stresses"

Lauritzen, T., W. L. Bell, G. M. Konze, J. M. Rosa, S. Vaidyanathan und F. A. Garner. Effects of tensile and compressive stresses on irradiation-induced swelling in AISI 316. [LMFBR]. Office of Scientific and Technical Information (OSTI), Mai 1985. http://dx.doi.org/10.2172/5534996.

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Teysseyre, S. Effect of Swelling on Irradiation-Assisted Stress Corrosion Cracking. Office of Scientific and Technical Information (OSTI), Juli 2017. http://dx.doi.org/10.2172/1483829.

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Teysseyre, Sebastien Paul. Study of the Effect of Swelling on Irradiation Assisted Stress Corrosion Cracking. Office of Scientific and Technical Information (OSTI), September 2016. http://dx.doi.org/10.2172/1364496.

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Vorobjev, A. N., S. I. Porollo und Yu V. Konobeev. Irradiation creep and stress-enhanced swelling of Fe-16Cr-15Ni-Nb austenitic stainless steel in BN-350. Office of Scientific and Technical Information (OSTI), April 1997. http://dx.doi.org/10.2172/543298.

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Snyder, Victor A., Dani Or, Amos Hadas und S. Assouline. Characterization of Post-Tillage Soil Fragmentation and Rejoining Affecting Soil Pore Space Evolution and Transport Properties. United States Department of Agriculture, April 2002. http://dx.doi.org/10.32747/2002.7580670.bard.

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Tillage modifies soil structure, altering conditions for plant growth and transport processes through the soil. However, the resulting loose structure is unstable and susceptible to collapse due to aggregate fragmentation during wetting and drying cycles, and coalescense of moist aggregates by internal capillary forces and external compactive stresses. Presently, limited understanding of these complex processes often leads to consideration of the soil plow layer as a static porous medium. With the purpose of filling some of this knowledge gap, the objectives of this Project were to: 1) Identify and quantify the major factors causing breakdown of primary soil fragments produced by tillage into smaller secondary fragments; 2) Identify and quantify the. physical processes involved in the coalescence of primary and secondary fragments and surfaces of weakness; 3) Measure temporal changes in pore-size distributions and hydraulic properties of reconstructed aggregate beds as a function of specified initial conditions and wetting/drying events; and 4) Construct a process-based model of post-tillage changes in soil structural and hydraulic properties of the plow layer and validate it against field experiments. A dynamic theory of capillary-driven plastic deformation of adjoining aggregates was developed, where instantaneous rate of change in geometry of aggregates and inter-aggregate pores was related to current geometry of the solid-gas-liquid system and measured soil rheological functions. The theory and supporting data showed that consolidation of aggregate beds is largely an event-driven process, restricted to a fairly narrow range of soil water contents where capillary suction is great enough to generate coalescence but where soil mechanical strength is still low enough to allow plastic deforn1ation of aggregates. The theory was also used to explain effects of transient external loading on compaction of aggregate beds. A stochastic forInalism was developed for modeling soil pore space evolution, based on the Fokker Planck equation (FPE). Analytical solutions for the FPE were developed, with parameters which can be measured empirically or related to the mechanistic aggregate deformation model. Pre-existing results from field experiments were used to illustrate how the FPE formalism can be applied to field data. Fragmentation of soil clods after tillage was observed to be an event-driven (as opposed to continuous) process that occurred only during wetting, and only as clods approached the saturation point. The major mechanism of fragmentation of large aggregates seemed to be differential soil swelling behind the wetting front. Aggregate "explosion" due to air entrapment seemed limited to small aggregates wetted simultaneously over their entire surface. Breakdown of large aggregates from 11 clay soils during successive wetting and drying cycles produced fragment size distributions which differed primarily by a scale factor l (essentially equivalent to the Van Bavel mean weight diameter), so that evolution of fragment size distributions could be modeled in terms of changes in l. For a given number of wetting and drying cycles, l decreased systematically with increasing plasticity index. When air-dry soil clods were slightly weakened by a single wetting event, and then allowed to "age" for six weeks at constant high water content, drop-shatter resistance in aged relative to non-aged clods was found to increase in proportion to plasticity index. This seemed consistent with the rheological model, which predicts faster plastic coalescence around small voids and sharp cracks (with resulting soil strengthening) in soils with low resistance to plastic yield and flow. A new theory of crack growth in "idealized" elastoplastic materials was formulated, with potential application to soil fracture phenomena. The theory was preliminarily (and successfully) tested using carbon steel, a ductile material which closely approximates ideal elastoplastic behavior, and for which the necessary fracture data existed in the literature.

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