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Research paper thumbnail of Shotcrete at Early Ages: Comparison of Test Results With a Thermo-Chemo-Micromechanics-Based Model for Shotcrete

Research paper thumbnail of MULTISCALE CONTINUUM MECHANICS OF CEMENTITIOUS MATERIALS: CREEP AND STRENGTH

multiscalemodelingofconcrete.com

ABSTRACT Cementitious materials are hierarchically organized, microheterogeneous media, ie charac... more ABSTRACT Cementitious materials are hierarchically organized, microheterogeneous media, ie characteristic heterogeneities are found at different microscopic scales of observation. Because of hydration, the microstructure of cementitious materials undergoes ...

Research paper thumbnail of Computational Simulation of the Mechanobiological Regulation of Bone Remodeling by Means of a Coupled Systems Biology-Micromechanical Approach

… /765: Telehealth/766: …, Jan 1, 2012

ABSTRACT Bone remodeling involves the coordinated removal of bone by osteoclasts and addition of ... more ABSTRACT Bone remodeling involves the coordinated removal of bone by osteoclasts and addition of bone by osteoblasts, a process that is modulated by the prevailing mechanical environment. Here we present a new computational model of bone remodeling, based on ...

Research paper thumbnail of Investigation of coupled geometrical and mechanical feedback controls in bone remodelling---A theoretical approach

arXiv preprint arXiv: …, Jan 1, 2012

Bone is a biomaterial undergoing continuous renewal. The renewal process is known as bone remodel... more Bone is a biomaterial undergoing continuous renewal. The renewal process is known as bone remodelling and is operated by bone-resorbing cells (osteoclasts) and bone-forming cells (osteoblasts). An important function of bone remodelling is the repair of microcracks accumulating in the bone matrix due to mechanical loading. Cell-cell communication between cells of the osteoclastic lineage and cells of the osteoblastic lineage is thought to couple resorption and formation so as to preserve bone integrity and achieve homeostatic bone renewal. Both biochemical and biomechanical regulatory mechanisms have been identified in this coupling. Many bone pathologies are associated with an alteration of bone cell interactions and a consequent disruption of bone homeostasis. In osteoporosis, for example, this disruption leads to long-term bone loss and fragility, and can ultimately result in fractures.

Research paper thumbnail of Computational Multiscale Model for NATM Tunnels: Micromechanics-Supported Hybrid Analyses

Multiscale Methods in …, Jan 1, 2011

Knowledge of the stress state in shotcrete tunnel shells is a necessary requirement to assess the... more Knowledge of the stress state in shotcrete tunnel shells is a necessary requirement to assess the safety of these structures. Estimation of these stresses from measured 3D tunnel shell displacement requires material models for shotcrete. Preferably such models should ...

Research paper thumbnail of Mechanobiological regulation of bone remodeling--Theoretical development of a coupled systems biology-micromechanical approach

arXiv preprint arXiv: …, Jan 1, 2012

Research paper thumbnail of Finite Volume model for diffusion-and activation-controlled pitting corrosion of stainless steel

Computer Methods in Applied Mechanics and …, Jan 1, 2009

Steel corrosion plays an adversary, but central role in different technological fields. Reasonabl... more Steel corrosion plays an adversary, but central role in different technological fields. Reasonable modeling of corrosion calls for a profound theoretical study of the underlying mechanisms. The present paper is concerned with mathematical modeling of (localized) ...

Research paper thumbnail of Micromechanics of bone tissue-engineering scaffolds, based on resolution error-cleared computer tomography

Biomaterials, Jan 1, 2009

Synchrotron radiation micro-computed tomography (SRmCT) revealed the microstructure of a CEL2 gla... more Synchrotron radiation micro-computed tomography (SRmCT) revealed the microstructure of a CEL2 glass-ceramic scaffold with macropores of several hundred microns characteristic length, in terms of the voxel-by-voxel 3D distribution of the attenuation coefficients throughout the scanned space. The probability density function of all attenuation coefficients related to the macroporous space inside the scaffold gives access to the tomograph-specific machine error included in the SRmCT measurements (also referred to as instrumental resolution function). After Lorentz function-based clearing of the measured CT data from the systematic resolution error, the voxel-specific attenuation information of the voxels representing the solid skeleton is translated into the composition of the material inside one voxel, in terms of the nanoporosity embedded in a dense CEL2 glass-ceramic matrix. Based on voxel-invariant elastic properties of dense CEL2 glass-ceramic, continuum micromechanics allows for translation of the voxel-specific nanoporosity into voxel-specific elastic properties. They serve as input for Finite Element analyses of the scaffold structure. Young's modulus of a specific CT-scanned macroporous scaffold sample, predicted from a Finite Element simulation of a uniaxial compression test, agrees well with the experimental value obtained from an ultrasonic test on the same sample. This highlights the satisfactory predictive capabilities of the presented approach.

Research paper thumbnail of Stable pitting corrosion of stainless steel as diffusion-controlled dissolution process with a sharp moving electrode boundary

Corrosion science, Jan 1, 2007

This contribution is devoted to explanation and prediction of corrosion pit propagation or stable... more This contribution is devoted to explanation and prediction of corrosion pit propagation or stable pit growth, governed by ion transport properties in electrolytic solutions by deriving the (3D) mass balance for a body hosting a sharp dissolution front which separates the solid electrode from liquid electrolyte. The model is completed by Fick's law of diffusion, governing the behavior of the dissolved metal ions.

Research paper thumbnail of From micron-sized needle-shaped hydrates to meter-sized shotcrete tunnel shells: micromechanical upscaling of stiffness and strength of hydrating shotcrete

Acta Geotechnica, Jan 1, 2008

Knowledge on the stresses in shotcrete tunnel shells is of great importance, as to assess their s... more Knowledge on the stresses in shotcrete tunnel shells is of great importance, as to assess their safety against severe cracking or failure. Estimation of these stresses from 3D optical displacement measurements requires shotcrete material models, which may preferentially consider variations in the water-cement and aggregate-cement ratios. Therefore, we employ two representative volume elements within a continuum micromechanics framework: the first one relates to cement paste (with a spherical material phase representing cement clinker grains, needle-shaped hydrate phases with isotropically distributed spatial orientations, a spherical water phase, and a spherical air phase; all being in mutual contact), and the second one relates to shotcrete (with phases representing cement paste and aggregates, whereby aggregate inclusions are embedded into a matrix made up by cement paste). Elasticity homogenization follows selfconsistent schemes (at the cement paste level) and Mori-Tanaka estimates (at the shotcrete level), and stress peaks in the hydrates related to quasi-brittle material failure are estimated by second-order phase averages derived from the RVE-related elastic energy. The latter permits upscaling from the hydrate strength to the shotcrete strength. Experimental data from resonant frequency tests, ultrasonics tests, adiabatic tests, uniaxial compression tests, and nanoindentation tests suggest that shotcrete elasticity and strength can be reasonably predicted from mixture-and hydration-independent elastic properties of aggregates, clinker, hydrates, water, and air, and from strength properties of hydrates. At the structural level, the micromechanics model, when combined with 3D displacement measurements, predicts that a decrease of the water-cement ratio increases the safety of the shotcrete tunnel shell.

Research paper thumbnail of Shotcrete at Early Ages: Comparison of Test Results With a Thermo-Chemo-Micromechanics-Based Model for Shotcrete

Research paper thumbnail of MULTISCALE CONTINUUM MECHANICS OF CEMENTITIOUS MATERIALS: CREEP AND STRENGTH

multiscalemodelingofconcrete.com

ABSTRACT Cementitious materials are hierarchically organized, microheterogeneous media, ie charac... more ABSTRACT Cementitious materials are hierarchically organized, microheterogeneous media, ie characteristic heterogeneities are found at different microscopic scales of observation. Because of hydration, the microstructure of cementitious materials undergoes ...

Research paper thumbnail of Computational Simulation of the Mechanobiological Regulation of Bone Remodeling by Means of a Coupled Systems Biology-Micromechanical Approach

… /765: Telehealth/766: …, Jan 1, 2012

ABSTRACT Bone remodeling involves the coordinated removal of bone by osteoclasts and addition of ... more ABSTRACT Bone remodeling involves the coordinated removal of bone by osteoclasts and addition of bone by osteoblasts, a process that is modulated by the prevailing mechanical environment. Here we present a new computational model of bone remodeling, based on ...

Research paper thumbnail of Investigation of coupled geometrical and mechanical feedback controls in bone remodelling---A theoretical approach

arXiv preprint arXiv: …, Jan 1, 2012

Bone is a biomaterial undergoing continuous renewal. The renewal process is known as bone remodel... more Bone is a biomaterial undergoing continuous renewal. The renewal process is known as bone remodelling and is operated by bone-resorbing cells (osteoclasts) and bone-forming cells (osteoblasts). An important function of bone remodelling is the repair of microcracks accumulating in the bone matrix due to mechanical loading. Cell-cell communication between cells of the osteoclastic lineage and cells of the osteoblastic lineage is thought to couple resorption and formation so as to preserve bone integrity and achieve homeostatic bone renewal. Both biochemical and biomechanical regulatory mechanisms have been identified in this coupling. Many bone pathologies are associated with an alteration of bone cell interactions and a consequent disruption of bone homeostasis. In osteoporosis, for example, this disruption leads to long-term bone loss and fragility, and can ultimately result in fractures.

Research paper thumbnail of Computational Multiscale Model for NATM Tunnels: Micromechanics-Supported Hybrid Analyses

Multiscale Methods in …, Jan 1, 2011

Knowledge of the stress state in shotcrete tunnel shells is a necessary requirement to assess the... more Knowledge of the stress state in shotcrete tunnel shells is a necessary requirement to assess the safety of these structures. Estimation of these stresses from measured 3D tunnel shell displacement requires material models for shotcrete. Preferably such models should ...

Research paper thumbnail of Mechanobiological regulation of bone remodeling--Theoretical development of a coupled systems biology-micromechanical approach

arXiv preprint arXiv: …, Jan 1, 2012

Research paper thumbnail of Finite Volume model for diffusion-and activation-controlled pitting corrosion of stainless steel

Computer Methods in Applied Mechanics and …, Jan 1, 2009

Steel corrosion plays an adversary, but central role in different technological fields. Reasonabl... more Steel corrosion plays an adversary, but central role in different technological fields. Reasonable modeling of corrosion calls for a profound theoretical study of the underlying mechanisms. The present paper is concerned with mathematical modeling of (localized) ...

Research paper thumbnail of Micromechanics of bone tissue-engineering scaffolds, based on resolution error-cleared computer tomography

Biomaterials, Jan 1, 2009

Synchrotron radiation micro-computed tomography (SRmCT) revealed the microstructure of a CEL2 gla... more Synchrotron radiation micro-computed tomography (SRmCT) revealed the microstructure of a CEL2 glass-ceramic scaffold with macropores of several hundred microns characteristic length, in terms of the voxel-by-voxel 3D distribution of the attenuation coefficients throughout the scanned space. The probability density function of all attenuation coefficients related to the macroporous space inside the scaffold gives access to the tomograph-specific machine error included in the SRmCT measurements (also referred to as instrumental resolution function). After Lorentz function-based clearing of the measured CT data from the systematic resolution error, the voxel-specific attenuation information of the voxels representing the solid skeleton is translated into the composition of the material inside one voxel, in terms of the nanoporosity embedded in a dense CEL2 glass-ceramic matrix. Based on voxel-invariant elastic properties of dense CEL2 glass-ceramic, continuum micromechanics allows for translation of the voxel-specific nanoporosity into voxel-specific elastic properties. They serve as input for Finite Element analyses of the scaffold structure. Young's modulus of a specific CT-scanned macroporous scaffold sample, predicted from a Finite Element simulation of a uniaxial compression test, agrees well with the experimental value obtained from an ultrasonic test on the same sample. This highlights the satisfactory predictive capabilities of the presented approach.

Research paper thumbnail of Stable pitting corrosion of stainless steel as diffusion-controlled dissolution process with a sharp moving electrode boundary

Corrosion science, Jan 1, 2007

This contribution is devoted to explanation and prediction of corrosion pit propagation or stable... more This contribution is devoted to explanation and prediction of corrosion pit propagation or stable pit growth, governed by ion transport properties in electrolytic solutions by deriving the (3D) mass balance for a body hosting a sharp dissolution front which separates the solid electrode from liquid electrolyte. The model is completed by Fick's law of diffusion, governing the behavior of the dissolved metal ions.

Research paper thumbnail of From micron-sized needle-shaped hydrates to meter-sized shotcrete tunnel shells: micromechanical upscaling of stiffness and strength of hydrating shotcrete

Acta Geotechnica, Jan 1, 2008

Knowledge on the stresses in shotcrete tunnel shells is of great importance, as to assess their s... more Knowledge on the stresses in shotcrete tunnel shells is of great importance, as to assess their safety against severe cracking or failure. Estimation of these stresses from 3D optical displacement measurements requires shotcrete material models, which may preferentially consider variations in the water-cement and aggregate-cement ratios. Therefore, we employ two representative volume elements within a continuum micromechanics framework: the first one relates to cement paste (with a spherical material phase representing cement clinker grains, needle-shaped hydrate phases with isotropically distributed spatial orientations, a spherical water phase, and a spherical air phase; all being in mutual contact), and the second one relates to shotcrete (with phases representing cement paste and aggregates, whereby aggregate inclusions are embedded into a matrix made up by cement paste). Elasticity homogenization follows selfconsistent schemes (at the cement paste level) and Mori-Tanaka estimates (at the shotcrete level), and stress peaks in the hydrates related to quasi-brittle material failure are estimated by second-order phase averages derived from the RVE-related elastic energy. The latter permits upscaling from the hydrate strength to the shotcrete strength. Experimental data from resonant frequency tests, ultrasonics tests, adiabatic tests, uniaxial compression tests, and nanoindentation tests suggest that shotcrete elasticity and strength can be reasonably predicted from mixture-and hydration-independent elastic properties of aggregates, clinker, hydrates, water, and air, and from strength properties of hydrates. At the structural level, the micromechanics model, when combined with 3D displacement measurements, predicts that a decrease of the water-cement ratio increases the safety of the shotcrete tunnel shell.