- Dynamical fracture behavior of materials under high strain rate is of great interest for materials science and practical applications.
- In a new paper led by our recent graduate Jet Lem, we study fracture of borosilicate glass on the nanosecond time scale by focusing laser-generated surface acoustic waves (SAWs).
- A picosecond pulse focused into a ring generates a high-amplitude SAW pulse converging to the center of the ring on a glass sample. Interferometric measurements of the surface displacement with a femtosecond probe pulse indicate that the tensile stress at the focus reaches 11 GPa, with the strain rate as high as ~108 s-1.
- When tensile stress reaches ~6 GPa, we observe fracture at the focal point, and a piece of material is ejected.
- Surprisingly, when we further increase the laser pulse energy and tensile stress reaches ~8 GPa, fracture ceases, and the sample withstands tensile stress up to 11 GPa without fracture. This is the highest tensile stress a bulk glass sample has withstood in any experiment and is close to the theoretical strength limit of silica glasses.
- Raman spectroscopy and nanoindentation measurements of recovered samples indicate structural changes in the material subjected to high-amplitude SAW pulses; in particular, Raman spectra indicate significant changes in the topology and coordination numbers of silicon and boron atoms in the amorphous network.
- We suggest that the observed atomic rearrangements serve as a high-strain-rate toughening mechanism leading to enhanced fracture toughness.
- Read the paper: J. Lem, E. R. Sung, A. A. Maznev, Y. Kai, A. F. Schwartzman, S. E.Kooi, and K. A. Nelson, Anomalous fracture behavior in borosilicate glass facilitated by stress-induced molecular rearrangements, PNAS 122, e2516249122 (2025).
Figure 1. (Top) Interferometric images showing displacement of the glass surface caused by SAWs converged at the center of the ring at a pump–probe delay of 22.5 ns for three excitation laser pulse energies. (Bottom) Corresponding SEM images of recovered samples. The laser energy and SAW amplitude increase from left to right. Surprisingly, fracture at the center of the ring ceases at highest amplitudes.