Effect of temperature on hardness and indentation cracking of fused silica

The fracture behavior induced by Vickers indentations in fused silica was investigated as a function of temperature. Indentations were performed from room temperature to 400 °C in air. The indentations and the crack pattern formed were analyzed by optical and scanning electron microscopy. The hardness at room temperature was 7.3 ± 0.3 GPa and decreased to 4.2 ± 0.1 GPa at 400 °C. Cone and radial cracks were observed at all temperatures. The radial crack length increased with temperature for a constant load. Lateral and median cracks were present under the indenter, and their expansion was constrained by cone cracks nucleated during the loading-unloading cycle. The threshold loads for cone and radial crack nucleation increased with temperature. The results are discussed in terms of the elastic modulus/hardness ratio variation with temperature.