Dynamic Equibiaxial Flexural Strength of Borosilicate Glass at High Temperatures

A novel high temperature ring-on-ring Kolsky bar technique was employed to investigate the dynamic equibiaxial flexural strength of borosilicate glass at temperatures ranging from room temperature up to 750°C. This technique provided non-contact heating of the glass specimen and prevented thermal shocks in the specimen. Experimental results at the loading rate of 22.5 MN/s showed significant temperature dependence on the flexural strength. To explore the mechanisms of this temperature effect, controlled surface cracks were introduced on the tensile surface of the glass specimens using a Vickers indentation technique. These surface cracks were then heat treated under the same thermal histories as those tested in the high temperature dynamic experiments. The evolution of crack morphologies at 200°C, 550°C and 650°C were examined. The results indicate that residual stress relaxation may play an important role in the strengthening below 200°C, while crack healing and blunting may account for the strengthening above 500°C.