13 - Mechanical Properties of Aerogels

Summary

Numerous daily-life materials exhibit a porous structure, e.g., foams made from different polymers (polystyrene, polyurethane), clays, tiles, bricks, oxide ceramics, bones, sponges, wood or diatoms. In many cases, the mechanical properties can be described by simple scaling laws with the relative or envelope density being the decisive factor. It is generally agreed that similar scaling laws apply to aerogels and xerogels, but the special nanostructured nature of aerogels and the mode used to form them out of a solution of monomers or polymers make an essential difference. A brief discussion of the conventional approach for closed and open cell foams or honeycombs based on the famous book written by Lorna J.Gibson and Michael F. Ashby on porous materials is given and extended to aerogels. Beforewe discuss aerogels, we briefly give for newcomers in the field of mechanical properties some textbook knowledge about mechanical testing. The chapter deals then with elastic and plastic properties of aerogels, compares modelling with experimental results and discusses deviations from classical porous media theory observed in aerogels.