Role of structural relaxations in the fracture of vitreous silica

The double cleavage drilled compression fracture mechanics specimen was used to obtain crack velocity data for vitreous silica in vacuum conditions at temperatures of 100 and 300 K. We observed stable crack propagation over a velocity range between 10−9 and 10−2 m/s. The measured fracture rate dependence with applied stress was modeled using a global energy balance approach that incorporated energy losses due to the anelastic response of the material in the stress field of the propagating crack. Measured mechanical loss data for vitreous silica were incorporated into an anelastic fracture model to produce qualitative agreement with the measured fracture behavior. These results indicate that the anelastic response of silicate glasses can contribute significantly to the measured fracture energy. This interpretation of silicate glass fracture suggests a new approach to design glass compositions for improved mechanical performance and provides a more complete picture of the atomic scale processes that control the macroscopic fracture energy of amorphous materials.