FRACTURE-MECHANICS MODEL FOR SUBTHRESHOLD INDENTATION FLAWS .2. NONEQUILIBRIUM FRACTURE

In Part II of this two-part study we extend the shear-fault-microcrack model to non-equilibrium fracture, to allow for rate effects in the critical instability configurations in chemically interactive environments. The "calibrated" K-fields of Part I are combined with independently evaluated crack velocity functions to determine kinetic conditions for microcrack extension. The analysis enables evaluation of (i) a time delay in radial crack pop-in from a subthreshold flaw; (ii) a time dependence in the strength characteristics, in both the subthreshold and postthreshold domains. Comparisons with delayed pop-in and strength-stressing-rate literature data for silicate glasses in moist environments indicate that the analysis is capable of quantitative predictions of kinetic characteristics. In the strength data, the model accounts for the relatively high magnitudes, scatter and fatigue susceptibilities in the subthreshold region.