QUantitative analysis by Image Correlation of localised stress enhanced nanoscaled phenomenon in GLASS – QUIC Glass

"Glass is certainly one of the oldest (7 000 B.C. for the first pure known glass) and most important materials in our society, widely used in many different areas either as a structural material (wind shield, aerial footbridge linking two buildings in Rotterdam...), an optical component (lenses, fibers), a substrate in electronics or as a bio-compatible and bio-active material in life science or even as a decorative tool. Although glass is characterized by its optical transparency, it is its particular atomic structure that makes it so interesting. Glass is an amorphous solid whose structure does not exhibit any long range order (i.e. nanometer scale for silica glass). Moreover, the infinite variability of possible compositions leads to a large variety of possible properties and subsequent applications. Nevertheless, glasses suffer from a common disease, i.e. a brittle behavior (no plastic deformation before rupture) and a low fracture toughness compare to the one of metals. - Recently neodymium-doped phosphate glass slabs were developed for the new mega Joule Laser (LMJ in France and NIF in USA) and used as amplifiers. Under the combined action of humidity and thermal cycling originating from LASER's beams some of those expensive slabs were fractured. In its final version the LASER will contain 3500 slabs, each of them costing the price of a Lexus car. A study of the fracture behavior of this material under similar conditions prior testing would have certainly provide the knowledge to anticipate such a problem, therefore saving time and money. - The awareness of the influence of the chemical composition of a glass on its mechanical behavior and especially its properties regarding crack propagation is therefore of paramount importance. Thus mechanisms of crack propagation need to be understood and tools relevant to their study developed. - - This project is composed of three different but connected parts: - 1) Investigation of nanoscaled phenomenon at crack tips in glass - The crack propagation in glass is a very complex phenomenon, which is multiscaled (macro, micro and nano) and trans-disciplinary from the mechanisms at play at the near tip region (ion exchange, dissolution, creation of a modified layer along the crack lips and a modified zone ahead of the crack tip enhanced by the presence of a mechanical stress field). The subcritical crack propagation (<10-8 m/s)) in the presence of a corrosive environment in oxide glasses as well as the existence of a fatigue limit below which the crack does not move are good illustration of this complexity. Thus the aim is to identify and quantify the mechanisms responsible for both the subcritical crack growth phenomenon and the existence of the fatigue limit through an experimental study of the fracture behavior of original glass compositions (oxides, chalcogenides glasses...) in particular environment and the use of instrumental technique and tools developed in §2 giving either topographical or chemical information related to the nanometer scale. - - 2) Quantitative three dimensional analysis of AFM pictures by digital image correlation (DIC) (A neat tool that needs to be developed and tested!) - - The aim is to develop and apply DIC to AFM images either as a tool providing quantitative three dimensional information regarding three dimensional displacement field (micro indentation, fiber testing,...) or shape evolution of objects over time (localized dissolution, crystallization,...) at the nano-micro scale. This technique could be implemented into the AFM software as an auto-calibration routine (dimensional calibration and correction of the non linearity). - - 3) Micro indentation/scratching and localized stress enhanced phenomenon as a possible way for glass surface micro patterning - - Currently under a patenting process this third point is both interesting from its potential application as a new technique for a precise micro patterning of glass surface and the science hided behind. The ...