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Papers by celine mallet

Springer water, Nov 23, 2022

L'objet de cette thèse est l’étude du comportement des fissures dans le verre. En particulier... more L'objet de cette thèse est l’étude du comportement des fissures dans le verre. En particulier, l’évaluationde l’effet à long terme des contraintes en compression, est étudié par des essais de fluage. Le dispositifexpérimental utilisé est une presse triaxiale qui permet de confiner des échantillons cylindriques et de leurappliquer des contraintes axiales, une pression de pore ainsi qu’une variation de température. Un réseaude capteurs fixés sur chaque échantillon permet de mesurer la déformation, les vitesses de propagation desondes élastiques et les émissions acoustiques. Les échantillons de verre fournis pour cette étude sont fabriquéspar le CEA de Marcoule. Nous avons observé que le verre sain présente un comportement élastiquefragileet une grande résistance mécanique. Un réseau de fissures est ensuite introduit par choc thermique.L’étude de la microstructure du réseau initial a révélé que le choc thermique induit des contraintes detension aux bords de l’échantillon qui nuclée...

L'objectif de ce travail est de contribuer à comprendre le comportement irréversible des maté... more L'objectif de ce travail est de contribuer à comprendre le comportement irréversible des matériaux dû à l'endommagement en étudiant l'influence de la fissuration sur les propriétés physiques et de transfert des matériaux après différentes sollicitations thermiques. Les matériaux considérés ont été choisis avec une microstructure différente permettant de montrer également l'impact de la microstructure sur l'apparition de la fissure. Un béton à granulats calcaire a été comparé à une roche calcaire très poreuse. Les mesures de vitesse des ondes élastiques, de porosité et de conductivité thermique ont été effectuées sur les échantillons après le traitement thermique choisi ici comme sollicitation pour étudier la fissuration. Trois protocoles différents ont été utilisés : choc thermique, augmentation progressive à haute température et cycles thermiques répétés entre la température ambiante et une température plus importante. La comparaison montre une influence signifi...

Étude de la fissuration des verres de stockage Comportement en condition de stockage géologique

Le verre est un materiau utilise, entre autres, par la France pour confiner les dechets nucleaire... more Le verre est un materiau utilise, entre autres, par la France pour confiner les dechets nucleaires de haute activite a vie longue. Ce procede de vitrification permet de confiner la radioactivite et de l’isoler du milieu naturel. Cependant, lors de la production de ces colis, des fissures apparaissent lors du refroidissement du verre. La fracturation a pour effet d’augmenter la surface potentielle d’echange dechet/environnement. Une circulation de fluide pourrait alors entrainer un relâchement des radionucleides dans l’environnement. Les contraintes lithostatiques liees aux conditions de stockage en profondeur peuvent induire une pression qui contribuera a fermer les fissures. Cependant, a long terme, une propagation des fissures peut avoir lieu. L’objet de cette these est d’evaluer l’effet du temps en condition de compression par des essais de fluage. Cette etude experimentale est realisee en laboratoire. Le dispositif experimental utilise est une presse triaxiale qui permet de conf...

Pure and Applied Geophysics, 2020

Journal of Building Engineering, 2019

Proceedings of the 7th International Conference on Environment and Engineering Geophysics & Summit Forum of Chinese Academy of Engineering on Engineering Science and Technology, 2016

The presented work takes place in the context of the storage of vitrified radioactive wastes. The... more The presented work takes place in the context of the storage of vitrified radioactive wastes. The mechanical behavior of crack in glass under pressure at low strain rate is of great interest. The present work is focused on the time dependency of crack propagation in glass. Experiments are performed in triaxial conditions on thermally cracked boro-silicate glass samples. The initial crack network is introduced through a thermal shock (the sample is slowly heated up to 300°C and then it is quenched into water at ambient temperature). The creep tests are performed by increasing the axial stress step by step (at constant confining pressure, temperature and pore fluid pressure). Results show that during creep tests, dilatancy is observed. This is not the case for regular triaxial test. The dilatancy is correlated to a non-zero acoustic emission rate that is evidenced by the sub-critical crack propagation. This crack growth induced localized failures. In addition, increasing temperature i...

Mechanics of Time-Dependent Materials, 2015

ABSTRACT We investigate pore fluid effects due to surface energy variation or due to chemical cor... more ABSTRACT We investigate pore fluid effects due to surface energy variation or due to chemical corrosion in cracked glass. Both effects have been documented through experimental tests on cracked borosilicate glass samples. Creep tests have been performed to investigate the slow crack propagation behavior. We compared the dry case (saturated with argon gas), the nonreactive water saturated case (commercial mineralized water), and the distilled and deionized water saturated case (pure water). Chemical corrosion effects have been observed and evidenced from pH and water composition evolution of the pure water. Then, the comparison of the dry case, the mineral water saturated case, and the corrosion case allow to (i) evidence the mechanical effect of the presence of a pore fluid and (ii) show also the chemical effect of a glass dissolution. Both effects enhance subcritical crack propagation.

International Journal of Fracture, 2014

ABSTRACT A crack network is introduced in glass by quenching heated samples. The sharp variation ... more ABSTRACT A crack network is introduced in glass by quenching heated samples. The sharp variation of temperature at the sample boundaries leads to tensile stresses that nucleate cracks. Then, they propagate in the entire sample. Quenching has been performed at 100, 200 and 300 ◦C. Cracks have been imaged with a scanning electron microscope. A transverse isotropic crack network is observed. Crack length and orientation have been measured. Obtained crack density has been compared to that inferred from elastic wave velocity measurements using effective medium theory. Cracked samples have been then submitted to creep tests. Two samples have been recovered, one before its failure and another after. Our observations show that vertical crack propagation takes place during brittle creep and that tertiary creep leads to a localized failure in a shear plane. The damaged and post-mortem microstructural networks have been documented.

ABSTRACT The context of our study is the observation of the mechanical behaviour of glass used fo... more ABSTRACT The context of our study is the observation of the mechanical behaviour of glass used for the storage of radioactive wastes. This implies to measure the crack propagation characteristics in glass. Results on the investigation of the micromechanics of creep under triaxial loading conditions are presented in the framework of this study. We performed the experiments in a triaxial cell, with pore fluid pressure, on boro-silicate glass. The chemical composition of the investigated glass is very close to the composition of waste vitrified packages. The matrix of the original glass (OG) is perfectly amorphous, without porosity. A few isolated air bubbles are trapped during the glass flow. Cracks are introduced in the OG through thermal shocks. The evolution of deformation (axial and radial strain) is measured using strain gages. The elastic P and S wave velocities and the acoustic emissions (AE) are also recorded. An experiment in dry conditions was performed (the pore fluid was argon gas) with a confining pressure fixed at 15 MPa. Stress step tests were performed in order to get creep data. A similar experiment was performed in water saturated conditions. Crack-closure is first observed at very low strains. Then elastic deformation is observed up to a stress level where elastic anisotropy develops. This can be clearly detected from ɛ Thomsen parameter increase. At last, at a deviatoric stress of 175 MPa (in dry conditions), we observe dilatancy. This behaviour has never been observed in original glass. Indeed, the OG behaviour is perfectly elastic and brittle. In addition, the constant stress tests show that dilatancy develops during a time constant that depends on the stress level. It can be inferred that crack propagation takes place during the constant stress steps. This behaviour is under investigation. We are also quantifying the velocity of the crack propagation by modelling this phenomenon. Indeed, the crack density can be expressed as a volumic strain, ɛv = πξρc. Then, using a model of penny shaped cracks of a radius, "a", we can express the crack density as: ρc = N/V a3 (for N cracks in a volume V). Knowing that ξ is the crack aspect ratio we can estimate ɛv using in a first approximation that ξ is a constant. Thus the variation of ɛv with time can be directly related to crack propagation È§.

ABSTRACT The context of our study is the observation of the time-dependent deformation of cracked... more ABSTRACT The context of our study is the observation of the time-dependent deformation of cracked glass. The aim of our study is to observe the slow crack propagation, to quantify it and to predict finally the creep behavior. We performed creep experiments in compaction conditions in a triaxial cell, on cracked boro-silicate glass samples. The chemical composition of the investigated glass is very close to the composition of waste vitrified packages. The matrix of the original glass (OG) is perfectly amorphous, without porosity. A few isolated air bubbles are trapped during the glass flow. Cracks are introduced in the OG through thermal shocks. Strain and acoustic emission (AE) are recorded. Several experiments are performed at different confining pressures (15 or 25 MPa), different pore fluid conditions (with argon gas, considered as the dry case, with tap water saturated porosity, or with distilled water) and different temperatures (ambiant temperature, 50oC or 80oC). Linear increase of the volumetric strain is first observed. A dilatancy increase is recorded. Note that dilatancy does not appear in constant strain rate tests. Constant stress tests show that dilatancy develops during a time interval that depends on the stress level. In addition AE rate are recorded. A non zero AE rate is an evidence of crack propagation. We use a micro-mechanical model that gives the stress intensity factor at the crack tips. This factor depends on stress and geometrical parameters (all known). An exponential law describe the rate of crack propagation, as a function of temperature, environment and applied stresses. This model allows us to predict the creep rate in glass. Assuming a constant crack aspect ratio, crack length and volumetric strain are related. The volumetric strain rate is calculated from model and compared to the data.

ABSTRACT We investigate how cracks develop and propagate in synthetic glass samples. Cracks are i... more ABSTRACT We investigate how cracks develop and propagate in synthetic glass samples. Cracks are introduced in glass by a thermal shock of 300oC. Crack network is documented from optical and electronic microscopy on these samples that have been submitted to a thermal shock only. Samples are cylinder of 80 mm length and 40 mm diameter. Sections were cut along the cylinder axis and perpendicular to it. Using SEM, crack lengths and apertures can be measured. Optical microscopy allows to get the crack distribution over the entire sample. The sample average crack length is 3 mm. The average aperture is 6 ± 3μm. There is however a clear difference between the sample core, where the crack network has approximatively a transverse isotrope symmetry and the outer ring, where cracks are smaller and more numerous. By measuring before and after the thermal treatment the radial P and S wave velocities in room conditions, we can determine the total crack density which is 0.24. Thermally cracked samples, as described above, were submitted to creep tests. Constant axial stress and lateral stress were applied. Several experiments were performed at different stress values. Samples are saturated for 48 hours (to get an homogeneous pore fluid distribution), the axial stress is increased up to 80% of the sample strength. Stress step tests were performed in order to get creep data. The evolution of strain (axial and radial strain) is measured using strain gages, gap sensors (for the global axial strain) and pore volume change (for the volumetric strain). Creep data are interpreted as evidence of sub-critical crack growth in the cracked glass samples. The above microstructural observations are used, together with a crack propagation model, to account for the creep behavior. Assuming that (i) the observed volumetric strain rate is due to crack propagation and (ii) crack aspect ratio is constant we calculate the creep rate. We obtain some value on the crack propagation during a 24 hours of constant stress test. At each of these test, crack propagate of 0.3 to 0.4 mm. From the initial average crack length of 3 mm, the crack reach the size of 5.8 mm at the end of a complete creep test (with 8 constant stress step of 24 hours).

Journal of Geophysical Research: Solid Earth, 2015

An experimental work is presented that aimed at improving our understanding of the mechanical evo... more An experimental work is presented that aimed at improving our understanding of the mechanical evolution of cracks under brittle creep conditions. Brittle creep may be an important slow deformation process in the Earth's crust. Synthetic glass samples have been used to observe and document brittle creep due to slow crack‐propagation. A crack density of 0.05 was introduced in intact synthetic glass samples by thermal shock. Creep tests were performed at constant confining pressure (15 MPa) for water saturated conditions. Data were obtained by maintaining the differential‐stress constant in steps of 24 h duration. A set of sensors allowed us to record strains and acoustic emissions during creep. The effect of temperature on creep was investigated from ambient temperature to 70°C. The activation energy for crack growth was found to be 32 kJ/mol. In secondary creep, a large dilatancy was observed that did not occur in constant strain rate tests. This is correlated to acoustic emissio...