Anomalous fracture toughness enhancement in glass facilitated by dynamic strain-induced defect formation

Fracture of borosilicate glass was investigated using laser-induced converging surface acoustic waves (SAWs). Strain amplitudes were interrogated by ultrafast interferometric imaging, capturing peak surface displacements generated by the converging SAWs. The peak displacements show a monotonic increase with increased laser fluence. Above a given fluence threshold, damage is consistently observed in the glass samples, characterized by fracture and ejection of material at the focus of the converging SAW. However, upon further fluence increase fracture is no longer observed. To understand this anomalous behavior, we conducted Raman spectroscopy on shock recovered samples. The Raman spectra revealed an increase in triply coordinate silicon and boron defect species in samples above the second fluence threshold. Such defects in glass are known to facilitate plastic deformation, owing to their increased translational and rotational freedom. This observation points to the ability of dynamic strain-induced defect formation to serve as a mechanism for enhanced fracture toughness in amorphous materials.