Kinetics of Indentation Cracking in Glass

The propagation of indentation radial cracks in soda-lime silicate glass is measured as a function of time after indentation. Rapid lift-off of the indenter from the specimen surface causes a step-function perturbation in the radial crack mechanical energy release rate, thus providing access to a large range of observable crack velocities in the indentation stress field. Analysis of the data shows distinct threshold, reaction-limited, and transport-limited behavior in the crack velocity responses, in agreement with measurements made using macroscopic crack geometries. Atomistic models of fracture kinetics in reactive environments are fit to the data and are deconvoluted to yield the underlying atomic-scale, bond-rupture parameters. These latter are used to calculate potential functions for activated fracture and predict crack velocity responses as a function of temperature and pressure.