Micromechanical properties of silica aerogels

Aerogels are nanostructured highly porous solids that present properties which are very different from other materials, i.e., extremely low densities. In this letter, the mechanical properties of aerogels have been studied with a nondestructive microindentation technique. This technique enables the continuous measurement of load-displacement curves during loading and unloading cycles by using very small indentation loads (similar to 1 mN), small enough to prevent cracking of the aerogels. The samples studied show two different types of mechanical behaviors; the low-density aerogels are elastic, while the denser aerogels behave as elastoplastic materials. Young's modulus, hardness, and the elastic parameter have been evaluated for these aerogel samples. Power function relationships have been found between these mechanical parameters and the aerogel densities. (C) 1999 American Institute of Physics. [S0003-6951(99)03631-1].