Strength and fracture in strong glasses

Abstract

Abstract The technological relevance of structural glasses has led to increased efforts to resolve structures and to gain insight into the structure-properties relationship that can be exploited for the design of new materials. During the past few years, there have been a large number of computer simulations to model amorphous structures and to study the mechanical properties of glassy systems. Among the mechanical properties the formation and the evolution of cracks greatly change the performance of every material. The traditional approach to brittle fracture is the study of continuum models, where the stress at the crack tip in an ideally brittle material is singular; since breaking individual bonds at the crack tip is of fundamental importance for crack growth in brittle fracture, it is not clear how accurate a continuum description of brittle fracture is. In strong glasses, which are non-equilibrium systems, the properties depend on the cooling rate at which the sample has been quenched; so the structure is not statistically homogeneous and the local strength may differ from the average value; the stress threshold at which one crack starts to propagate is a random variable and depends almost entirely on the extreme-value statistics of the largest defects. Here we try to connect the theoretical strength, the ageing effects on the mechanical properties and the local fracture toughness distribution in this class of materials.