Fracture of transparent brittle solids due to stress pulses generated by a Q-switched ruby laser

Abstract

A Q-switched laser beam with a rise time of 10 ns was directed through a glass plate and absorbed by an opaque layer of silver paint to generate a compressive stress wave of comparable duration, with a peak stress of up to 1 GN m−2, measured using a new technique involving a `Sandia quartz gauge'. On reflection from the free surface, the stress wave becomes tensile and can damage the surface and cause spallation. There is a well-defined stress level for the onset of spallation which depends upon the size and density of the initial surface microcracks. A single hertzian cone crack, 240 μm long, required a peak stress of 0·05-0·07 GN m−2, in agreement with theoretical predictions on the basis of a quasistatic fracture model. In contrast, the threshold stresses for abraded surfaces were one or two orders of magnitude smaller than the predicted values, suggesting a fundamental difference between the response of single- and multiple-cracked surfaces to short-duration stress waves. A second higher threshold is observed at which cracks spread inwards from the surface and concentrate in a planar region parallel to the surface.

Model Inspired by Population Genetics to Study Fragmentation of Brittle Plates

“…The RCG model is defined on a two-dimensional lattice composed of A = L 2 sites with periodic boundary conditions, which simulates a two-dimensional plate whose height h << L. We assume that due to the impact there is a stress pulse that diffuses or disperses in the system starting from the impact point [14]. During this diffusion process some connections between lattice sites are broken depending on their particular mechanical strength.…”