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Pushing the Frontier of Brittlness
Damage Resistant Glasses

Final Report Summary - DAMREG (Pushing the Frontier of BrittlnessDamage Resistant Glasses)

The fundamental objective of the project was to propose new methods and new glasses and glass-based materials opposing a better resistance to mechanical damage (fracture, indentation cracking, brittleness). The first essential steps were to identify the key material characteristics governing the formation of cracks at the glass surface, to clarify the response of a glass and a glass-matrix particulate composite depending on the composition, and second phase volume fraction, and to address the question of the fracture toughness (how it can be measured? What it means?). At the end of the project it is considered that most of these objectives were achieved beyond expectation. A "damage map" was proposed as a guideline toward surface damage resistance as a function of the glass properties (and composition). The incidence of the materials parameters (matrix and particles for a composite) on the crack tip behavior was studied by means of in-depth modeling and numerical simulation and validated by 3D tomography observations. Then, reliable and self-consistent methods were developed to estimate fracture toughness, and a theoretical model was proposed to independently reach an ab-initio value for the toughness from the composition. Both experimental and theoretical values are in excellent agreement. Probably the most challenging goal of the project was to design new materials on the basis of the theoretical analysis of the problem of damage in glass. In this regard, the project was also very successful and some groundbreaking results were obtained. New ideas developed within the project included the feasibility for converting the elastic energy stored before fracture into optical or electrical effects. Two main research directions were explored: mechano-optical and mechano-electrical couplings. Some glass matrix/ceramic particles composites emitting a visible light under mechanical loading (mechanoluminescence) were fabricated and the constitutive law for the coupling was determined. A glass-ceramic material exhibiting piezoelectric effects was also synthesized. This latter material was found to experience a strong drop of his viscosity in the Tg range under an electric tension. Besides, some crack-healing effects were demonstrated by applying laser or magnetic fields to glasses containing nanoparticles of gold or magnetite respectively. These latter materials are still under survey although the project reached its end.