Selected Constitutive Models for Simulating the Hygromechanical Response of Wood

Henrik Lund Frandsen

Selected Constitutive Models for Simulating the Hygromechanical Response of Wood

Henrik Lund Frandsen

Publikation: Ph.d.-afhandling

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Abstract

Denne afhandling er en samling af artikler. Tre af artiklerne, I, VI og VII, er kun publiceret i denne afhandling, det være sig en introduktionsartikel og to såkaldte diskussionsartikler. Artiklerne II, III og V er publiceret eller godkendt til publicering i det internationale tidsskrift Holzforschung. Artikel IV er en konferenceartikel præsenteret på 19th Nordic Seminar on Computational Mechanics, Lund, Sverige, 2006.

Artikel I: Teorierne for fænomenerne, der leder til det hygromekaniske respons af træ, relaterer sig til dets ortotrope cellulære struktur og de hydrofile og hydrofobe polymerer, der udgør trævævet. Denne introduktionsartikel formidler disse teorier for den hydromekaniske respons og tilvejebringer hermed også en referenceramme og den røde tråd i nærværende afhandling.

Artikel II: Flere fugttransportveje og langsom sorption medfører (såkaldte) ikke-Fickske effekter. Dette fordrer en ny type multifaset transportmodel. I denne artikel bliver den essentielle sorptionshastighedsmodel indeholdt i den såkaldte multi-Fickske model revideret. Sorptionshastighedsmodellen bliver undersøgt på basis af eksisterende eksperimentelle resulter. En model for desorptionshastighed svarende til modellen for adsorptionshastighed bliver foreslået. Derudover bliver randbetingelserne diskuteret på basis af afvigelser, som er fundet i lignende forskning på fugttransport i papirstakke.

Artikel III: En ny sorptionshysterese-model, som er egnet til implementering i en numerisk metode, udvikles. Den forudgående såkaldte scanning-kurve bliver modelleret med et udtryk på lukket form, som kun afhænger af den nuværende relative fugtighed i luften og det nuværende fugtindhold i træet. Derudover er udtrykkene for scanning-kurverne formuleret uafhængigt af de temperatur- og træsortsafhængige randkurver.

Artikel IV: Sorptionshysterese-modellen udviklet i Artikel III bliver anvendt på to forskellige træsorter og på afbleget kraft-karton.

Artikel V: Sorptionshysterese-modellen implementeres i den multi-Fickske model, hvormed både ikke-Fickske effekter og hysteresis kan simuleres samtidig. Et nøglepunkt for denne implementering er definitionen af træets tilstand som et punkt i hysterese-rummet, der er uafhængig af tilstanden af vanddampen i cellehulrummene. To metoder bliver udviklet og testet ved implementering i en kommerciel software

Artikel VI: I denne artikel bliver temperaturafhængigheden af den multi-Fickske model med hysterese diskuteret. De konstitutive fugttransport-modeller bliver koblet med en varmetransportmodel, hvilket frembringer led, som beskriver de såkaldte Dofour- og Sorret-effekter, hvor der dog her er taget højde for flere faser og hysterese.

Artikel VII: Modelleringen af de transversale koblinger i krybning af træ diskuteres på basis af de eksperimentelle observationer og nye teoretiske fund omkring tidsafhængige Poissonforhold. En ny ortotrop krybningsmodel, som giver retningsuafhængige krybningshastigheder, bliver foreslået. Derudover bliver forsøgsopstilling for et igangværende eksperimentelt studium af fænomenet præsenteret.

Originalsprog	Engelsk
Udgivelsessted	Aalborg
Udgiver	Department of Civil Engineering, Aalborg University
Status	Udgivet - 2007

Emneord

Hygromechanical Responses
Wood
Wood Structures
Multi-Fickian Effects
Non-Fickian Effects
Moisture
Moisture Transport
Hysteresis Models

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Selected Constitutive Models for Simulating the Hygromechanical Response of WoodForlagets udgivne version, 7,6 MB

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PhD Project: Selected Constitutive Models for Simulating the Hygromechanical Response of Wood
Frandsen, H. L., Svensson, S. & Jensen, H. M.
<ingen navn>
01/11/2003 → 22/02/2008
Projekter: Projekt › Ph.d.-projekt

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Citationsformater

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title = "Selected Constitutive Models for Simulating the Hygromechanical Response of Wood",

abstract = "The present thesis is a compilation of papers. Three of the papers, I , VI and VII, are published in this thesis only, i.e., an introductory paper and two so-called discussion papers. The papers II, III and V have been published in the international journal, Holzforschung. Paper IV is a conference paper presented at the 19th Nordic Seminar on Computational Mechanics, Lund, Sweden, 2006. Paper I: The theories for the phenomena leading to hygromechanical response of wood relate to the orthotropic cellular structure and the hydrophilic and hydrophobic polymers constituting the cells. This introductory paper presents these theories for the hygromechanical response and hereby also provides the frame of reference and the connecting thread of the present thesis.Paper II: Multiple paths for moisture transport and slow sorption yield non-Fickian effects. This calls for a new type of multi-phase transport model. In this paper a so-called multi-Fickian model is revised with respect to the incorporated essential sorption rate model. Based on existing experimental results the sorption rate model is studied. A desorption rate model analogous to the adsorption rate model is proposed. Furthermore, the boundary conditions are discussed based on discrepancies found for similar research on moisture transport in paper stacks.Paper III: A new sorption hysteresis model suitable for implementation into a numerical method is developed. The prevailing so-called scanning curves are modeled by closed-form expressions, which only depend on the current relative humidity of the air and current moisture content of the wood. Furthermore, the expressions for the scanning curves are formulated independent of the temperature and species-dependent boundary curves.Paper IV: The sorption hysteresis model developed in paper III is applied to two different wood species and to bleach-kraft paperboard.Paper V: The sorption hysteresis model is implemented into the multi-Fickian model allowing simultaneous simulation of non-Fickian effects and hysteresis. A key point for this implementation is definition of the condition of wood as a state in the sorption hysteresis space, which is independent of the condition of water vapor in the lumens. Two approaches are developed and tested by implementation into commercial software.Paper VI: The temperature dependencies of the hysteretic multi-Fickian moisture transport model are discussed. The constitutive moisture transport models are coupled with a heat transport model yielding terms that describe the so-called Dufour and Sorret effects, however, with multiple phases and hysteresis included.Paper VII: In this paper the modeling of transverse couplings in creep of wood are discussed based on experimental observation of time dependent Poisson ratios and new theoretical findings on the Poisson ratio. A new orthotropic creep model, which provides directionally independent creep rates, is proposed. Furthermore, the procedure for an ongoing experimental study of the phenomenon is presented.",

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author = "Frandsen, {Henrik Lund}",

year = "2007",

language = "English",

series = "DCE Thesis",

publisher = "Department of Civil Engineering, Aalborg University",

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N2 - The present thesis is a compilation of papers. Three of the papers, I , VI and VII, are published in this thesis only, i.e., an introductory paper and two so-called discussion papers. The papers II, III and V have been published in the international journal, Holzforschung. Paper IV is a conference paper presented at the 19th Nordic Seminar on Computational Mechanics, Lund, Sweden, 2006. Paper I: The theories for the phenomena leading to hygromechanical response of wood relate to the orthotropic cellular structure and the hydrophilic and hydrophobic polymers constituting the cells. This introductory paper presents these theories for the hygromechanical response and hereby also provides the frame of reference and the connecting thread of the present thesis.Paper II: Multiple paths for moisture transport and slow sorption yield non-Fickian effects. This calls for a new type of multi-phase transport model. In this paper a so-called multi-Fickian model is revised with respect to the incorporated essential sorption rate model. Based on existing experimental results the sorption rate model is studied. A desorption rate model analogous to the adsorption rate model is proposed. Furthermore, the boundary conditions are discussed based on discrepancies found for similar research on moisture transport in paper stacks.Paper III: A new sorption hysteresis model suitable for implementation into a numerical method is developed. The prevailing so-called scanning curves are modeled by closed-form expressions, which only depend on the current relative humidity of the air and current moisture content of the wood. Furthermore, the expressions for the scanning curves are formulated independent of the temperature and species-dependent boundary curves.Paper IV: The sorption hysteresis model developed in paper III is applied to two different wood species and to bleach-kraft paperboard.Paper V: The sorption hysteresis model is implemented into the multi-Fickian model allowing simultaneous simulation of non-Fickian effects and hysteresis. A key point for this implementation is definition of the condition of wood as a state in the sorption hysteresis space, which is independent of the condition of water vapor in the lumens. Two approaches are developed and tested by implementation into commercial software.Paper VI: The temperature dependencies of the hysteretic multi-Fickian moisture transport model are discussed. The constitutive moisture transport models are coupled with a heat transport model yielding terms that describe the so-called Dufour and Sorret effects, however, with multiple phases and hysteresis included.Paper VII: In this paper the modeling of transverse couplings in creep of wood are discussed based on experimental observation of time dependent Poisson ratios and new theoretical findings on the Poisson ratio. A new orthotropic creep model, which provides directionally independent creep rates, is proposed. Furthermore, the procedure for an ongoing experimental study of the phenomenon is presented.

AB - The present thesis is a compilation of papers. Three of the papers, I , VI and VII, are published in this thesis only, i.e., an introductory paper and two so-called discussion papers. The papers II, III and V have been published in the international journal, Holzforschung. Paper IV is a conference paper presented at the 19th Nordic Seminar on Computational Mechanics, Lund, Sweden, 2006. Paper I: The theories for the phenomena leading to hygromechanical response of wood relate to the orthotropic cellular structure and the hydrophilic and hydrophobic polymers constituting the cells. This introductory paper presents these theories for the hygromechanical response and hereby also provides the frame of reference and the connecting thread of the present thesis.Paper II: Multiple paths for moisture transport and slow sorption yield non-Fickian effects. This calls for a new type of multi-phase transport model. In this paper a so-called multi-Fickian model is revised with respect to the incorporated essential sorption rate model. Based on existing experimental results the sorption rate model is studied. A desorption rate model analogous to the adsorption rate model is proposed. Furthermore, the boundary conditions are discussed based on discrepancies found for similar research on moisture transport in paper stacks.Paper III: A new sorption hysteresis model suitable for implementation into a numerical method is developed. The prevailing so-called scanning curves are modeled by closed-form expressions, which only depend on the current relative humidity of the air and current moisture content of the wood. Furthermore, the expressions for the scanning curves are formulated independent of the temperature and species-dependent boundary curves.Paper IV: The sorption hysteresis model developed in paper III is applied to two different wood species and to bleach-kraft paperboard.Paper V: The sorption hysteresis model is implemented into the multi-Fickian model allowing simultaneous simulation of non-Fickian effects and hysteresis. A key point for this implementation is definition of the condition of wood as a state in the sorption hysteresis space, which is independent of the condition of water vapor in the lumens. Two approaches are developed and tested by implementation into commercial software.Paper VI: The temperature dependencies of the hysteretic multi-Fickian moisture transport model are discussed. The constitutive moisture transport models are coupled with a heat transport model yielding terms that describe the so-called Dufour and Sorret effects, however, with multiple phases and hysteresis included.Paper VII: In this paper the modeling of transverse couplings in creep of wood are discussed based on experimental observation of time dependent Poisson ratios and new theoretical findings on the Poisson ratio. A new orthotropic creep model, which provides directionally independent creep rates, is proposed. Furthermore, the procedure for an ongoing experimental study of the phenomenon is presented.

KW - Hygromechanical Responses

KW - Wood

KW - Wood Structures

KW - Multi-Fickian Effects

KW - Non-Fickian Effects

KW - Moisture

KW - Moisture Transport

KW - Hysteresis Models

KW - Hygromechanical Responses

KW - Wood

KW - Wood Structures

KW - Multi-Fickian Effects

KW - Non-Fickian Effects

KW - Moisture

KW - Moisture Transport

KW - Hysteresis Models

M3 - PhD thesis

T3 - DCE Thesis

PB - Department of Civil Engineering, Aalborg University

CY - Aalborg

ER -

Selected Constitutive Models for Simulating the Hygromechanical Response of Wood

Abstract

Emneord

Adgang til dokumentet

AUB Link

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Projekter

PhD Project: Selected Constitutive Models for Simulating the Hygromechanical Response of Wood

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