Mechanical properties of SiO₂aerogels

Abstract

Ultrasonic and static compression experiments were performed in the frequency range 50 kHz to 1 MHz in order to investigate the mechanical behaviour of silica aerogels as a function of internal gas pressure pG and external stress Pext. The measurement of longitudinal and transverse sound velocities allows the Young's modulus and the Poisson's ratio for aerogels of different densities to be determined upon variation of pG and Pext. For low-density aerogels ( rho approximately=100 kgm-3) the authors found a decrease in sound velocity upon evacuation. Surprisingly, the sound velocity decreases upon uniaxial compression with small loads. The most important finding from the static compression experiments is that low-density aerogels display creeping with a time constant of about 45 min.