Response of mechanical properties of glasses to their chemical, thermal and mechanical histories

Mechanical properties are a key factor to be considered when designing new glass compositions, optimizing glass processing parameters and defining the glass application fields. However, mechanical properties of glasses are complex values since they are influenced by many factors such as structure, surface, thermal history or excess entropy of the final glass state. Here I review recent progresses in understanding of the responses of mechanical properties of oxide glasses to the compositional variation, thermal history and mechanical deformation. The tensile strength, elastic modulus and hardness of glass fibers are dependent on the thermal history (measured as fictive temperature), tension, chemical composition and redox state. However, the fictive temperature affects the hardness of bulk glass in a complicated manner, i.e., the effect does not exhibit a clear regularity in the range of the fictive temperatures that we have measured so far. It depends on type of glass systems. This complicated effect is discussed in terms of glass structure, dynamics and relaxation behavior. Our recent experimental findings indicate that for oxide glass fibers the tensile strength, elastic modulus and hardness of glass fibers are strongly correlated with the glass composition, fictive temperature, axial tension, and redox state. This correlation is explained by considering both the bulk and the surface glass structure. Furthermore, the compositional dependence of the densification extent, plastic flow and micro-cracks occurring during indentation of a glass is discussed briefly. Finally I describe the future perspectives and challenges in understanding responses of mechanical properties of oxide glasses to compositional variation, thermal history and mechanical deformation.