Abstract
The sub-critical crack growth in hydrophobic (as prepared) and hydrophilic (oxidized) silica aerogel was studied using the Dynamic fatigue experiment and the Double-Cleavage-Drilled-Compression test (DCDC). The effect of oxidation treatment is clearly evidenced. The temperature and water vapor content dependence on the crack growth rate is measured between 22 °C and 110 °C with relative air moisture ranging from 5 to 80% RH. Like dense silica, crack growth velocities were found to decrease when increasing the temperature at a constant water vapor concentration. Surprisingly, the crack velocity also decreases when increasing water vapor content at constant temperature. Such a behavior is contrary to expected results usually encountered in glasses. We assume that a capillary condensation phenomenon of water vapor inside the aerogel porosity takes place, inducing internal compressive stresses.
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