Stress intensity factor in silica alcogels and aerogels

The stress intensity factor (K-IC) of alcogel and aerogel sets is measured by the single edge notched beam (SENB) technique. Sets of gels are made at various tetramethoxysilane (TMOS) content and gelation catalyst (neutral an d basic catalyst). It was found that the toughness increases with the TMOS content and is strongly enhanced by the supercritical drying (SD) step for the neutral set. The K-IC increase is associated to a higher load bearing a nd to the formation of new links during SD. The critical flaw size is calcu lated from K-IC and fracture stress. It is shown that the critical flaw siz e changes with the parameters TMOS%, catalyst and SD. This change can be co rrelated to the macropore volume evolution which suggests that macropores c an be considered as responsible for the failure. (C) 2000 Elsevier Science B.V. All rights reserved.