BOA Workshop Computational tools for Multiscale Modelling

BOA Workshop

Department of Chemistry, Virtasen Aukio 1, Helsinki - 31.01.2012

Computational tools for Multiscale Modelling – from biomaterials to bentonite

VTT, Knowledge Centre: Structural Performance, Team: Service Life

13/03/2012 2

Introduction

• Background on Multiscale Modelling of wood-based materials:

Improved Moisture

project, WoodWisdom-Net, 2007-2010, coordination:

VTT, partners: TUWien (Austria), MPA (Germany), KTH (Sweden), Harbin University (China).

• Current work on bentonite modelling: started within some Posiva

projects (and BOA).

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Multiscale of wood Hygro-thermal phenomena:

multiphase approach (water vapor and bound water phases, internal energy)

Improved Moisture

Multiphysics and Multiscale of wood-based biomaterials

Macroscale

Action E 55

Transient conditions

b 0 J n

a v s v v

v k p p

J n

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Multi-Fickian formulation of transient transport process in wood (natural environmental conditions, wood under FSP)

• 3 coupled macroscopic differential equations:

mass conservation for bound water

mass conservation for water vapor

energy conservation

Implementation in Uel subroutine/(Abaqus code)

Improved Moisture

sorption rate

bound water concentration

water vapour concentration

hentalpies

internal energy

temperature

+ boundary conditions

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Sorption isotherm and hysteresis curves used in multiphase models for wood

under natural environmental conditions

Frandsen H. L. and Svensson S. Implementation of sorption hysteresis in multi-Fickian moisture transport.

Holzforschung 2007; 61(6): 693-701

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Experimental experiments

for calculation of moisture profiles NMR

cylindrical samples

mini dessiccators

Bruker Avance II spectrometer at resonance frequency of 300 MHz (superconducting magnet and consol with

electronic devices).

The images covered a field of view of 20 mm with a spatial resolution of 78 µm.

geometry

boundary conditions

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Comparisons between experimental data and numerical results - Tangential uncoated case

Average values over the axis of the specimen (0-14 mm).

Dvinskikh, Sergey V., Henriksson, Marielle, Mendicino, Antonio Lorenzo, Fortino, Stefania, Toratti, Tomi.

(2011).NMR imaging study and multi-Fickian numerical simulation of moisture transfer in Norway spruce samples. Engineering Structures, 33 (11), 3079-3086.

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Multiscale Modelling of wood

50 µm

Different material properties for each layer and for early- and latewood

Homogenization methods

Influence of microfibril angle and orientation (based on nano-indentation tests)

Micromechanics FEM model of the unit wood cell, Abaqus Script implementation

Thermomechanics-based constitutive model at the macroscale

Recoverable mechanosorptive strain + irrecoverable mechanosorption

(plastic model)

hygroexpansion

viscoelastic creep

elastic strain

annual ring scale

material properties to:

Improved Moisture

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Some implementation details

moisture content and temperature histories from multiphase analysis

NOTE: general computational algorithm suitable also for general biomaterials and porous materials

• Fortino S., Mirianon F., Toratti T. (2009). A 3D moistur stress FEM analysis for time dependent problems in timber structures. Mech. of Time-Dep.

Mater. 13, 333–356.

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Microscale-mesoscale models for wood

Code for the generation of wood cells geometry (including latewood and earlywood layers). The

randomized geometry is useful to reproduce the tomography images.

Microscale (de Magristris and Salmén, 2008)

Computer tomography on fatigued wood (Lauri Salminen, 2011)

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Multiphase formulation of transient transport process in wood (high temperature processes)

•

2 coupled macroscopic differential equations including condensation of 4 equations related to water vapour, bound water, free water and

internal energy:

- mass conservation

- energy conservation

water moisture content

fluxes of water vapour, bound water and free water

Implementation in Uel subroutine/(Abaqus code)

temperature specific internal energies

h: enthalpies

+ boundary conditions

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Hygro-Thermo-Mechanical modelling for wood surface densification (

Expected result: prediction of the final density and control of

process parameters and

”spring-back” phenomenon Computational tool:

•Sequential Hygro-Thermo-Mechanical analysis

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Simulation of biomaterials production processes

Sequential Hygro-Thermo-(Chemo)-Mechanical analysis

Hygro-thermal analysis

Results to:

Static or dynamic stress analysis

Constitutive models based on micromechanics (Umat, Vmat subroutines)

Multiphase/multiphysics models (Uel, DFlux, Hetval subroutines)

Chemical effects

Molecular dynamics or energy approach lignocellulosic biomass

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Bentonite modelling Discussion

• Hygro-thermal problem (multiphase approach)

• Nonlinear material behaviour under strong compression :

- modified Drucker-Prager models (or similar) under strong compressive loads (on-going) - influence of hygro-thermal response and plastic strains on mechanical quantities, swelling - influence of grain size, friction

- initial density, initial water content - ...

• Thermo-Hygro-Mechanical modelling (similar scheme as for biomaterials)

• Chemical modelling: MD