Showing papers by "Tanguy Rouxel published in 2005"

Quantitative evaluation of indentation-induced densification in glass

Abstract: To estimate the ratio of densification to Vickers indentation volume, three-dimensional images of Vickers indentations on several glasses, including silicate glasses and bulk metallic glass (BMG), were obtained before and after annealing using an atomic force microscope. Large volume recovery of Vickers indentation by annealing was observed for all glasses but BMG. Following previous studies, this recovered volume almost corresponded to the densified volume under a Vickers indenter, and the compositional dependence of densification was discussed. The ratios of densification to the total indentation volume for silica and soda-lime glasses were 92% and 61%, respectively. It was concluded that densification was a general property for silicate glasses and that the ratios of densification to the total indentation volume for all the glasses correlated well with Poisson’s ratios of the glasses.

Structure–Property Correlations in Y–Ca–Mg–Sialon Glasses: Physical and Mechanical Properties

Abstract: The physical and mechanical properties of 12 glasses from the Y–(Mg,Ca)–Si–Al–O–N and (Mg,Ca)–Si–Al–O–N systems were investigated. The effect of the substitution of magnesium for calcium through two series of glasses, one consisting of oxides glasses and the other of glasses containing 6 at.% of nitrogen (15 e/o N), was considered. The change of the glass transition temperature through the glass series provides evidence for a mixed-alkaline-earth effect between magnesium and calcium species. The indentation hardness (H), Young's modulus (E), and indentation fracture toughness (KC) were found to increase significantly with either the magnesium or the nitrogen content, and nitrogen also seems to enhance the effect of magnesium on the properties. The network structure was analyzed both by 29Si and 27Al Magic Angle Spinning Nuclear Magnetic Resonance and by neutron scattering experiment, which allows for the estimation of some atomic bond lengths in such complex glasses. Nitrogen was found to have a significant structural effect on the magnesium environment and on the glass polymerization degree, and hence on the glass properties.

Creep Behavior of Soda‐Lime Glass in the 100–500 K Temperature Range by Indentation Creep Test

Abstract: The loading time and temperature dependences viscoelastic behavior of a soda-lime-silicate glass (SLS) were studied by indentation creep experiments. Experiments were conducted in air, water and silicone oil with 15–10 000 s loading times, and temperatures ranging between 100 and 500 K. The indentation size was found to depend much on the loading time and temperature. Hardness was found to decrease significantly with increasing loading time, even at 173 K, and to decrease rapidly with rising temperature, even well below the glass transition temperature (Tg). Water on the surface of glasses appeared to reduce the hardness and indentation viscosity of the glass.

Scratchability of Soda-Lime Silica (SLS) Glasses: Dynamic Fracture Analysis

Abstract: Grinding and polishing are widely used for glass machining with fine finished surfaces. These processes result from abrasion due to repeated contacts between hard sliding particles and the glass surface. The study of contact mechanics problem is of fundamental interest to understand the process of material removal in glasses. In order to get insight into this problem, an experimental set up was designed which allows a monotonic loading of the indenter combined with a controlled sliding of the specimen to simulate a slow abrasive machining process. In addition, the experiments are conducted with an in-situ video monitoring that allows for the observation of the different fracture phenomena beneath the indenter. Fracture surfaces were also studied using SEM and AFM for multi-scale investigation. Fracture analysis was carried on a standard float glass, four different SLS glasses and a fused silica glass. The observed phenomena were discussed in the light of the influence of the normal load and the chemical composition.

Mechanical Behavior of a Borosilicate Glass Under Aqueous Corrosion

Abstract: In France, fission products are being vitrified for a possible final geological disposal. Under disposal conditions, corrosion of the glass by groundwater as well as stress corrosion because of stresses occurring at surface flaws cannot be excluded. Within this framework, the mechanical behavior of the French simulated nuclear waste glass SON68 was studied by Vickers indentation and fracture experiments in air and in a corrosive solution. The glass was corroded at 90°C in a solution enriched with Si, B, and Na. The results showed that the glass corrosion enhances the cracks propagation relative to experiments in air. The indentation fracture toughness (KIC) obtained using a four-point bending test showed that the KIC of the glass decreased with increasing corrosion time.

Compressive Creep of a Fine‐Grained Poly crystal line Yttria

Abstract: Compressive creep of a high-purity fine-grained polycrystalline yttria ceramic processed by hot isostatic pressing has been investigated in the 1,130--1,210 C temperature range for stresses between 6 and 92 MPa. The main creep mechanism is grain boundary diffusion controlled by an interface reaction. The most striking feature is the strong dynamic grain growth whereas static grain growth is negligible in the studied temperature domain.

Fractographic Analysis of Surface Flaws in Glass

Abstract: Biaxial testing was used to get insight into the incidence of the surface flaw properties (size, shape) on the strength of float glass specimens. Grinding grooves, Vickers' indentations and scratches as defects were introduced at the surface of annealed float glass specimens. The machined and fractured surfaces were observed using optical and confocal microscopes. The influence of the flaw characteristics on the strength of glass was evaluated and analyzed in the light of the fracture mechanics.

Indentation and Scratching of Glass: Load, Composition and Temperature Effects

Abstract: The response of glass to mechanical contact has been the subject of numerous publications. However, most of the investigations were dedicated to standard window glasses, although there is a need for the characterization of functional glasses such as chalcogenide glasses and of newly developed structural glasses, including oxynitride and oxycarbide glasses. Besides, most investigators focused on the phenomenology and on the mechanics of contact damage and the incidences of the glass composition, the environment and the temperatures were little studied and thus remain poorly understood.

Insight into the Deformation Mechanisms under a Sharp Contact Loading in Glass by Atomic Force Microscopy

Abstract: The response of a material to a sharp contact loading, as in the case of Vickers indentation for instance, provides a unique insight into the material constitutive law, including elastic and irreversible deformation parameters as well. However, under such peculiar thermodynamical and mechanical conditions (the mean contact pressure on the contact area reaches values typically higher than 1 GPa, corresponding to the hardness of the material) the deformation processes are complex and the matter located just beneath -and around- the contact area may experience some structural changes and behave in a way different to the expected - or known - macroscopic behaviour. It is showed in this study by means of detailed topological investigations of the residual indentations by Atomic Force Microscopy (AFM) that the elastic recovery typically represents 50 to 70 % of the indentation volume at maximum load and that the densification contribution may reach 90 % of the residual deformation volume. Besides, most glasses exhibit indentation-creep phenomena, which become significant over time scale of only few minutes because of a pronounced shear-thinning behavior.