Physical aging in glasses and composites

Abstract

Physical aging is observed in all glassy materials because of the fact that they are out of equilibrium. The ways in which aging manifests itself are the results of the thermal history of the materials, the environment, and even the constraint of, e.g., fibers or particles. In the present chapter, the fundamentals of aging of glasses are summarized by considering first structural recovery, which is the kinetics of the thermodynamic-type variables such as volume or enthalpy, and its impact on the mechanical response, which is the physical aging. Linear viscoelastic and nonlinear viscoelastic properties as well as yield behaviors will be considered. Furthermore, we will consider environmental effects on physical aging behaviors. The work will end with a perspective on aging in composites and where further research is needed.