On the mechanical β relaxation in glass and its relation to the double-peak phenomenon in impulse excited vibration at high temperatures

A viscoelastic model is established to reveal the relation between α-β relaxation of glass and the double-peak phenomenon in the experiments of impulse excited vibration. In the modeling, the normal mode analysis (NMA) of potential energy landscape (PEL) picture is employed to describe mechanical α and β relaxations in a glassy material. The model indicates that a small β relaxation can lead to an apparent double-peak phenomenon resulted from the free vibration of a glass beam when the frequency of β relaxation peak is close to the natural frequency of specimen. The theoretical prediction is validated by the acoustic spectrum of a fluorosilicate glass beam excited by a mid-span impulse. Furthermore, the experimental results indicate a negative temperature-dependence of the frequency of β relaxation in the fluorosilicate glass S-FSL5 which can be explained based on the physical picture of fragmented oxide-network patches in liquid-like regions.