DIRECT MEASUREMENT OF SUBCRITICAL CRACK-GROWTH RATE IN MAGNESIUM ALUMINOSILICATE GLASS BY THE INDENTATION TECHNIQUE

Subcritical crack growth measurements were carried out on magnesium-aluminosilicate glass specimens using the indentation technique. Crack growth velocities were accurately measured between 10(-9) m/s and 10(-7) m/s. The subcritical crack growth susceptibility coefficient, N, was calculated to be 36.6 and 41. These values compare well with the values determined by the double torsion specimen containing a macro-crack. A macro-crack begins propagating at higher velocities (or higher loads) and it is impractical to maintain the experimental conditions for a substantial period of time before a velocity of 10(-9) m/s can be measured. Therefore, the present technique seems to be a viable alternative to measurement of specimens containing macro-cracks.