Saint-Martin-d'Hères - Domaine universitaire

Saint-Martin-d'Hères - Domaine universitaire

Some ceramic grades, such as silicon carbide (SiC) or alumina (Al2O3), are used as ballistic materials thanks to their excellent mechanical performances, such as their hardness, while being light, where weight gain is a major issue for the design of military equipment for personal and vehicle protection. Since the Vietnam War, ceramics have been largely used and integrated as front face in bilayer shielding to stop the threat of AP (Armour Piercing)-type projectiles during a ballistic impact. Nevertheless, the projectile leads to an intense damage in the ceramic due to, amongst other phenomena, a dynamic tensile loading that manifests by multiple cracking, called fragmentation, particularly unfavourable for the integrity of the ballistic protection and its capacity to deal with a second impact. In order to develop a more performing shielding material, it is essential to understand the link between the microstructure of ceramics, the damage generated under impact and their ballistic performances.

This thesis seeks to better understand the dynamic fragmentation phenomenon generated at high strain rates in high fracture-toughness ceramics, including a bio-inspired alumina material mimicking nacre microstructure. This artificial nacre is, a priori, more crack resistant than conventional ceramics as it is characterised by a high static fracture-toughness due to its specific “Brick-and-Mortar” (or BM) microstructure reproduced in the material called here MAINa.

Jury

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Some major results from the PhD: steel core extracted from API-BZ bullet with MAINa microstructure observed in Scanning Electron Microscopy (chapter 2); comparison between the experimental force-displacement response along with the numerical response using the identified experimental law of the steel core (chapter 3); numerical simulation of the penetration process of the steel core (800 m/s) in a SiC ceramic, 56 μs after impact (chapter 4); dynamic cracking of MAINa microstructure, tested in two orientations of platelets during Rockspall tests (chapter 5); multiple fragmentation of MAINa samples (0° orientation) after both Edge-On-Impact test in sarcophagus configuration and tandem test with tomographic segmentation (chapter 6).

• En savoir plus sur Thèse de Yannick Duplan

A distance, Saint-Martin-d'Hères - Domaine universitaire

J. Carlos Santamarina (Professor - KAUST) graduated from Universidad Nacional de Córdoba and completed graduate studies at the Universities of Maryland and Purdue. He taught at NYU-Polytechnic, the University of Waterloo and at Georgia Tech before joining KAUST in 2015. His research centers on the science of geomaterials and engineering solutions to address global energy challenges, with contributions from resource recovery to energy and waste geostorage. He delivered the 50th Terzaghi Lecture on Energy Geotechnology, was a British Geotechnical Association Touring Lecturer, and is member of both Argentinean National Academies. Former team members are professors at more than forty universities, researchers at national laboratories, or practicing engineers at leading organizations worldwide.

• En savoir plus sur J. Carlos Santamarina

Saint-Martin-d'Hères - Domaine universitaire

Introducing statistical mechanics framework into granular mechanics has been attempted both by physicists and mechanicians in recent decades. The talk overviews its recent outcomes and try to connects the two perspectives from physics and mechanics sides.

• En savoir plus sur Takashi Matsushima

Saint-Martin-d'Hères - Domaine universitaire

Granular media and concrete are the ubiquitous natural and construction materials. X-ray tomography (XRT) has been used throughout the past three decades to qualitatively and quantitatively study the kinematics of deformation in these materials from meso- to microscales. However, quantifying the microscopic mechanisms of stress transmission and energy dissipation in these materials has traditionally been limited to 2D model materials or 3D numerical simulations. Such information can provide insight into the validity of microscopic contact laws, the statistics of forces and energy dissipation, and the pre- and post-failure load sharing within the materials’ microstructures.

In this talk, I will discuss experiments employing in-situ XRT and 3D X-ray diffraction (3DXRD) measurements during the deformation of 3D granular materials and cement. Using 3DXRD, each particle in the granular materials and cements acts as a stress gauge, providing both the local elastic stress tensors and the orientations of material points within the microstructure. I will highlight experiments with granular materials in which we quantitatively measured inter-particle forces, constitutive law parameters, per-particle fracture stresses, and energy dissipation mechanisms at each inter-particle contact. I will highlight an experiment on micro-concrete in which we quantified the stress distribution throughout the microstructure before and after fracture. I will discuss ongoing and future research directions in geomaterials with combined XRT and 3DXRD.

• En savoir plus sur Ryan Hurley

Saint-Martin-d'Hères - Domaine universitaire

This doctoral thesis investigates the impact of the meso-scale heterogeneities of concrete (aggregates and macro-pores) on its macroscopic mechanical response. A combined numerical and experimental approach is adopted to study the progressive evolution of the 3D fracturing processes of micro-concrete specimens under uniaxial tension, uniaxial compression and triaxial compression.



Part of the originality of this work lies in the exploration of multiple loading paths on concrete samples of realistic composition (including cement, sand, aggregates and water) and in the in-situ nature of the experiments conducted. The experimental campaign is performed inside an x-ray scanner, which allows the internal structure of the material to be non-destructively captured and its evolution from the intact (before loading) until the damaged (after unloading) state to be followed and quantified. The 3D images coming from the x-ray scans are first analysed in order to quantitatively describe the morphology of the meso-structure (aggregates, mortar matrix and macro-pores). A timeseries analysis of the set of 3D images coming from each in-situ test follows, which allows for the measurement of the 3D kinematic fields (displacement and strain fields) throughout the experiments.



On the numerical side, the identified morphologies coming from the intact x-rays scans are given as an input to a FE meso-model with enhanced discontinuities. The originality of the numerical simulations comes from their 3D nature and the consideration of the actual meso-structure of the micro-concrete specimens, based on the segmentation of the three phases of the material. After a calibration of the model in uniaxial tension, its predictive ability is challenged under different stress paths in compression. An extensive comparison is presented between experimental and numerical observations, in terms of macroscopic responses, displacement fields, fracturing processes and failure patterns. The typical asymmetric behaviour of concrete in tension and compression, as well as the increase of strength and ductility with the increase of confinement are sufficiently captured numerically. Starting from an x-ray scan, it is shown that the model is able to satisfactorily Sreproduce some of the basic characteristic features of the failure modes observed experimentally for the different loading paths studied.

While validating the numerical results and through a combination of numerical and experimental observations, the significant impact of the meso-scale heterogeneities on the local failure mechanisms is revealed. It is shown that, for the studied material, the shape and location of the largest aggregates and macro-pores are essentially driving the fracture patterns under simple tension, simple compression and triaxial compression. The good correspondence between experiments and model strongly suggests that the explicit representation of these heterogeneities is the key feature that allows the predictive power of the model. A further insight into the impact of the meso-structure is obtained by investigating virtual concrete morphologies, generated by modifying the real meso-structures coming from the x-ray scans.

Jury

• En savoir plus sur Thèse de Olga Stamati

Saint-Martin-d'Hères - Domaine universitaire

The main objective of the thesis is to improve our understanding of faceting occurring during dry snow metamorphism. The thesis focuses on the interplay between heat and mass diffusion, and kinetic effects in the context of snow. For the first time, Diffraction Contrast Tomography (DCT) has been performed to monitor an experiment of temperature gradient metamorphism. The technique permits retrieval of the crystalline orientation of the grains constituting the microstructure of the sample. Links between orientation of crystals and mass fluxes were analyzed.

The study shows that kinetic differences between basal and prismatic faces have effects on phase change fluxes at the ice/air interface. From a numerical modeling point of view, a highly anisotropic kinetic coefficient has been taken into account for the evolution of the ice/air interface. The model uses the phase-field approach and couples phase changes to heat and water vapor diffusion.

The model was compared to an experiment of air cavity migration under a temperature gradient in a monocrystalline ice block monitored with X-ray microtomography, and to the growth of a negative crystal during a pumping experiment followed with optical microscopy. Such anisotropy permits reproduction of the observed faceting.

Finally, the potential of the proposed model to describe snow metamorphism is highlighted.

Jury

• En savoir plus sur Thèse de Rémi Granger

Saint-Martin-d'Hères - Domaine universitaire

Earth construction is widely used in a lot of developing countries where they still are the main technique of construction despite the dominance of modern construction techniques in urban areas. Studying the seismic vulnerability of such structures is then crucial since many of them are located in highly active seismic zones. Therefore, this study focused on analyzing the behavior of earth constructions, more specifically the adobe walls, thanks to numerical and experimental methods.

Two experimental tests were developed for this study. The first one is a shake table which permits to do dynamic tests by reproducing real seismic events. An important effort was carried out in order to enhance the control of the table and to check its performance via signal analysis. Then, a steel structure prototype was used to check the behavior of the table with additional payload. The second test is a pseudo dynamic test, known as a hybrid test that combines numerical and experimental aspects. The same steel prototype was used to validate the test workability. Then, the feedbacks of both experiments were compared to the results of numerical simulations.

The last part of the work was dedicated to the vulnerability analysis of adobe walls under seismic loading. A numerical model based on previous quasi-static tests on two earth masonry walls was created in Abaqus. It was followed by a parametrical study to assess the effect of some material parameters on the wall behavior. Then a dynamic experimental test was carried out on an adobe wall using the shake table. The experimental results were then compared to numerical ones that were obtained based on material characteristics extracted from different experimental tests on the adobe and the mortar, and done at material scale. Dynamic tests performed on the adobe wall and the numerical work allowed to predict the wall response and to study the damage patterns. Additional works to enhance the experimental apparatus performance as well as the numerical models will be done in order to optimize the tools for seismic analysis that were developed in this study.

 

• En savoir plus sur Thèse de Hala Damerji

Saint-Martin-d'Hères - Domaine universitaire

La conférence ICVPB2020 est une conférence internationale bi-annuelle qui rassemble entre 150 et 250 chercheurs et cliniciens autour des questions de physiologie et biomécanique de la voix humaine. Cette année 2020, pour la première fois dans l’histoire de cette conférence, elle est organisée sur le site de Grenoble, et se tiendra en ligne du fait de la pandémie (02 au 04 Décembre 2020 - https://icvpb2020.sciencesconf.org). Cette 12ième édition permettera de célébrer les 40 ans de l’histoire de cette conférence et des recherches internationales sur la physiologie et la biomécanique de la voix humaine.

Le laboratoire 3SR co-organise cet événement avec le laboratoire GIPSA-lab, en partenariat avec de nombreuses sociétés savantes françaises (Acoustique – SFA et GAP, Phoniatrie et Laryngologie – SFPL, Communication Parlée – AFCP, Biomécanique – SB), les réseaux de recherche Grenoblois (Fédération de Mécanique – Fed3G), la communauté des pédagogues de la voix (AFPC-EVTA France), les tutelles des laboratoires (CNRS, Grenoble INP, UGA), la région Auvergne Rhônes Alpes et trois sponsors industriels (NOVITOM, INSTRON, ZAION).

Annonce (PNG, 1.22 Mo)

• En savoir plus sur ICVPB 2020

Saint-Martin-d'Hères - Domaine universitaire

Ce pôle mène des recherches dans les domaines de la physique et des nanosciences, de la mécanique, de l’électronique, du génie électrique, de la science de matériaux, du génie des procédés et des sciences de l'ingénieur et de la production. Ces travaux ont des implications dans des domaines à fort enjeu sociétal, comme la santé, la transition énergétique et sa durabilité, le renouveau industriel et la société de l'information et de la communication. Ce pôle comporte 25 laboratoires, 453 chercheurs, 518 enseignants-chercheurs et 1200 doctorants.

Programme de la journée (PDF, 141.53 Ko)

• En savoir plus sur Journée du pôle PEM

Saint-Martin-d'Hères - Domaine universitaire

Les travaux menés dans cette thèse ont pour objectif d’étudier le comportement mécanique d’une poudre constituée de grains déformables en utilisant, de manière complémentaire, des essais expérimentaux et des outils numériques. Pour cela, une poudre polymère est testée mécaniquement dans un micro-tomographe à rayons X afin de déterminer et d’analyser l’évolution de la microstructure au cours du chargement. L’analyse des images 3D rend possible la modélisation du milieu granulaire par la méthode des éléments finis multi-particules. Cette méthode permet de simuler le comportement d’un ensemble de grains interagissant par contact auxquels sont attribués une loi de comportement élasto-plastique. Une méthode a été complètement développée afin de permettre cette analyse multi-échelles. La réponse ainsi simulée du milieu granulaire est comparable à celle observée dans l’expérimentation.

Le matériau constitutif du milieu granulaire est le polystyrène dont les géométries des grains sont relativement hétérogènes. La poudre est caractérisée mécaniquement par des essais de compression triaxiale de révolution menés à différentes pressions de confinement. Le dispositif de chargement triaxial est introduit dans un tomographe à rayons X afin de visualiser l’évolution de la microstructure granulaire au sein de l’échantillon pour plusieurs états de chargement. Un code de calcul de corrélation permet, à partir des volumes issus de la tomographie, de déterminer un champ de déplacement et, par la suite, un champ de déformation. L’analyse de la densité est également rendue possible grâce à la tomographie. Avec l’objectif d’étudier le comportement du milieu granulaire lors du chargement, les particules présentes dans les volumes issus de la tomographie sont identifiées individuellement, maillées puis introduites dans un modèle éléments finis multi-particules. Les conditions aux limites imposées à l’échantillon numérique sont générées en imposant aux grains en périphérie de l’échantillon des déplacements de même amplitude et de même direction que les déplacements calculés par la corrélation de volumes au niveau de ces mêmes grains.

Les simulations numériques éléments finis sont menées sur des volumes contenant plusieurs centaines de grains. Les calculs de déformation moyenne de ces volumes permettent une comparaison directe avec les déformations déduites de la corrélation des images 3D. Cette comparaison indique que la méthode de génération des conditions aux limites pour la simulation mécanique par éléments finis est valide. Il a cependant été remarqué que l’étude localisée de la densification de la poudre pour les grandes déformations est dépendante de la taille du volume simulé. Un calcul de contrainte moyennée sur le volume simulé est également mené afin de déterminer localement l’état de contrainte dans l’échantillon pour un comportement supposé du matériau constitutif des grains. Plusieurs simulations, menées en différents sous-volumes de l’échantillon rendent possible la génération d’un champ de contrainte. Compte tenu du nombre de calculs nécessaires pour aboutir à cette génération, seule l’évolution radiale de la contrainte a été estimée concernant les résultats présentés. Le calcul de la contrainte axiale par la simulation présente un autre avantage : le choix de certaines propriétés mécaniques du matériau constitutif des grains dans la simulation permet de se rapprocher de la contrainte axiale mesurée sur l’échantillon réel et donc de caractériser les propriétés mécaniques des grains en interaction.

Jury

• En savoir plus sur Thèse de Maxime Teil