Statistical analysis of propagation rates of indentation-induced radial cracks in soda-lime-silica glass

Due to the stochastic nature of crack nucleation by Vickers indentation, a statistical analysis of propagation rates of 185 radial cracks was performed. Crack growth was observed directly using a video camera with high image acquisition rate. It is found that propagation rates are controlled by the environmental reactions at the crack-tip shortly after their initiation (< 1 s). Calibration of the stress intensity K _I showed that the residual stress factor χ and the exponent n of the equation K _I = =χ Pc⁻ⁿ (with P = =load and c = =crack length) are broadly distributed among the 185 analyzed cracks, ranging from 10 ⁻¹⁶ to 10 ⁴ and from 0.1 to 5, respectively. For the most frequent crack, the equation K _I = =0.052 Pc ^−1.47 holds. The results show that correlations of indentation-induced crack length to stress intensity necessitate the use of statistical significant data that are calibrated by the environmental reactions at the crack-tip.