Plasticity at nanoindentation site in glass : a possible experimental benchmark for numerical modeling

We have recently developed a technique allowing for the 3 dimensional probing, with a nanometer scale resolution, of small volumes affected by plastic events at Nano indentation sites. This method is sensitive to the structural changes in the glassy network (number of SiO4 units per ring, Si-O-Si inter-tetrahedral angle, connectivity loss) resulting from the densification. The plastic zone due to structural modifications has an enhanced reaction rate which, if coupled with precise atomic force microscopy measurements (AFM), may be used for probing and rebuilt the densified volume beneath nano indentation or nano scratch imprints made on a glass surface. Instrumented nano indentations and scratches (250 µN to 10 mN range) were made on various glass compositions. The effect of the applied load on the size and the shape of the plastic zone size is reported and compared to numerical simulations

Guides optiques infrarouges pour la détection du CO2

session affiches A7 " Instrumentation, Caractérisation et Capteurs " [A7.1]National audienceL'équipe Verres et Céramiques développe des fibres optiques originales qui sont à la base de la réalisation de capteur optique opérant dans l'infrarouge. L'intérêt et le potentiel de ces capteurs ont été démontrés dans des domaines variés, notamment en biologie et en médecine. L'objet de ce travail consiste à exploiter ce savoir faire pour réaliser des guides optiques permettant la détection et le monitoring du CO2. Des premiers résultats ont été obtenus en transmission classique entre deux fibres infrarouges. Ils ont montré qu'il est possible de détecter jusqu'à 0.5% de CO2. L'objectif actuel est d'améliorer la sensibilité de détection au dioxyde de carbone par une augmentation de la surface de contact gaz-fibre, en utilisant des fibres microstructurées. Une autre voie consiste à fabriquer des guides planaires qui nous permettent d'envisager, à terme, la réalisation de micro-composants optiques en verre de chalcogénure avec une robustesse et une compacité accrue

Investigating ramp wave propagation inside silica glass with laser experiments and molecular simulations

Under elastic shock compression silica glass exhibits a very specific behaviour. A shock propagating inside a material is usually seen as the propagation of a discontinuity. However in silica glass, shocks are unstable and lead to the propagation of a ramp wave where the shock front becomes gradually larger over time. Ramp waves were already reported in the literature, however their origin remain uncertain. This work presents an original study combining laser shock-induced experiments and molecular dynamics simulation aiming to improve the understanding of the mechanisms involved. Experimental ramp waves were directly observed using shadowgraphy technique allowing for an estimation of the head and tail velocities. Molecular dynamics simulations were carried out in order to reproduce ramp waves and to gain insight into the material properties. Ramp waves were observed for both elastic and plastic shockwaves. In the latter case, the plastic waves were preceded by an elastic ramp precursor. The sound speed, related to the material compressibility, was found to decrease with increasing pressure, as observed experimentally for quasi-static hydrostatic loading, thus providing an explanation for the instabilities that lead to the propagation of ramp waves

Laser induced dynamic fracture of fused silica: Experiments and simulations

Fused silica samples were subjected to laser induced shock loading. Laser flux was varied in order to obtain different amounts and characteristics of damage in the samples. Three dimensional damage and fracture maps of two identical samples impacted by high and low laser flux values were obtained using both optical microscopy and X-ray computed micro-tomography. Three prevalent fracture and damage patterns were identified. Peridynamic approach was used to simulate the laser impact conditions on the samples in order to explain the causes of the observed fracture and damage morphologies. A proprietary shock physics code, ESTHER, was used to calculate the transient kinetic energy imparted to the samples based on the experimental laser flux values. The kinetic energy values were then integrated over time and provided target values to match for the peridynamic impact conditions. The main fracture patterns were captured by peridynamic simulations with reasonable quantitative accuracy. Explanations for initiation and propagation of each of the fracture patterns were presented based on the peridynamic dynamic fracture simulations. Limitations of the computational approach and recommendations for future work is provided

The seeds of divergence: the economy of French North America, 1688 to 1760

Generally, Canada has been ignored in the literature on the colonial origins of divergence with most of the attention going to the United States. Late nineteenth century estimates of income per capita show that Canada was relatively poorer than the United States and that within Canada, the French and Catholic population of Quebec was considerably poorer. Was this gap long standing? Some evidence has been advanced for earlier periods, but it is quite limited and not well-suited for comparison with other societies. This thesis aims to contribute both to Canadian economic history and to comparative work on inequality across nations during the early modern period. With the use of novel prices and wages from Quebec—which was then the largest settlement in Canada and under French rule—a price index, a series of real wages and a measurement of Gross Domestic Product (GDP) are constructed. They are used to shed light both on the course of economic development until the French were defeated by the British in 1760 and on standards of living in that colony relative to the mother country, France, as well as the American colonies. The work is divided into three components. The first component relates to the construction of a price index. The absence of such an index has been a thorn in the side of Canadian historians as it has limited the ability of historians to obtain real values of wages, output and living standards. This index shows that prices did not follow any trend and remained at a stable level. However, there were episodes of wide swings—mostly due to wars and the monetary experiment of playing card money. The creation of this index lays the foundation of the next component. The second component constructs a standardized real wage series in the form of welfare ratios (a consumption basket divided by nominal wage rate multiplied by length of work year) to compare Canada with France, England and Colonial America. Two measures are derived. The first relies on a “bare bones” definition of consumption with a large share of land-intensive goods. This measure indicates that Canada was poorer than England and Colonial America and not appreciably richer than France. However, this measure overestimates the relative position of Canada to the Old World because of the strong presence of land-intensive goods. A second measure is created using a “respectable” definition of consumption in which the basket includes a larger share of manufactured goods and capital-intensive goods. This second basket better reflects differences in living standards since the abundance of land in Canada (and Colonial America) made it easy to achieve bare subsistence, but the scarcity of capital and skilled labor made the consumption of luxuries and manufactured goods (clothing, lighting, imported goods) highly expensive. With this measure, the advantage of New France over France evaporates and turns slightly negative. In comparison with Britain and Colonial America, the gap widens appreciably. This element is the most important for future research. By showing a reversal because of a shift to a different type of basket, it shows that Old World and New World comparisons are very sensitive to how we measure the cost of living. Furthermore, there are no sustained improvements in living standards over the period regardless of the measure used. Gaps in living standards observed later in the nineteenth century existed as far back as the seventeenth century. In a wider American perspective that includes the Spanish colonies, Canada fares better. The third component computes a new series for Gross Domestic Product (GDP). This is to avoid problems associated with using real wages in the form of welfare ratios which assume a constant labor supply. This assumption is hard to defend in the case of Colonial Canada as there were many signs of increasing industriousness during the eighteenth and nineteenth centuries. The GDP series suggest no long-run trend in living standards (from 1688 to circa 1765). The long peace era of 1713 to 1740 was marked by modest economic growth which offset a steady decline that had started in 1688, but by 1760 (as a result of constant warfare) living standards had sunk below their 1688 levels. These developments are accompanied by observations that suggest that other indicators of living standard declined. The flat-lining of incomes is accompanied by substantial increases in the amount of time worked, rising mortality and rising infant mortality. In addition, comparisons of incomes with the American colonies confirm the results obtained with wages— Canada was considerably poorer. At the end, a long conclusion is provides an exploratory discussion of why Canada would have diverged early on. In structural terms, it is argued that the French colony was plagued by the problem of a small population which prohibited the existence of scale effects. In combination with the fact that it was dispersed throughout the territory, the small population of New France limited the scope for specialization and economies of scale. However, this problem was in part created, and in part aggravated, by institutional factors like seigneurial tenure. The colonial origins of French America’s divergence from the rest of North America are thus partly institutional

A nano meter scaled contribution to the understanding of glass mechanical behavior: crack propagation and plasticity

International audienc

Comportement mécanique des verres inorganiques du plus fragile au plus tenace

De nos jours il existe de nombreuses familles de verres (chalcogénures oxyazotés, oxycarbonés dont les propriétés et le comportement mécaénique sont parfois mal connus. Ce trail se décompose en trois étapes : une étude bibliographique de la structure de ces différentes familles de verres, la présentation des méthodes expérimentales utilisées, les résultats expérimentaux et leur interprétation. Les propréts mécaniques mesurées sont : les modules élastiques E,G et v obtenus par échographie ultrasonore, la dureté Meyer par indentation Vickers et la ténacité qui est obtenue par deux méthodes : l'I.F.M. (indentation fracture méthod) et la méthode de l'éprouvette entaillée en chevron sollicitée en flexion trois points. Une attention particulière est protée sur l'étude du comportement à l'indentation des différents matériaux. Ces propriétés sont discutées en fonction de la composition (par exemple le pourcentage de germanium et d'antimoine introduits pour les verres de chalcogénures). Un certain nombre de comportements caractéristiques ont été mis en évidence ; en particulier le retour élastique significatif après indentation et le fluage sous chargeRENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Tribologie des verres silicatés - Frottement et endommagement superficiel

National audienceSurface damage lies at the root of glass brittleness. In this article, the main causes of surface damage are described, starting from simple cracking induced by normal contact with a blunt indenter, up to scratch-induced damage and spalling. We also demonstrate a strong coupling between mechanical loading and chemical reactivity of silicate glasses, with implications for both (i) surface damage and crack propagation, and (ii) polishing and planarisation. A few examples of industrial glass protection processes are also given