Engraving glass prevents shattering

Drop a glass on the floor and the likelihood is it will smash; do the same with a seashell and it will probably stay intact.

The secret to why is held within the natural structure of the shell, which has just been revealed by researchers from McGill University in Canada.

Professor François Barthelat and colleagues in the Department of Mechanical Engineering studied the internal weak boundaries or edges found in natural materials like nacre and from that were able to develop a technique to make glass slides less brittle. They believe the method could be scaled up for any sized glass sheet.

“Mollusc shells are made up of about 95% chalk, which is very brittle in its pure form,” said Barthelat. “But nacre, or mother-of-pearl which coats the inner shells, is made up of microscopic tablets that are a bit like miniature Lego building blocks, is known to be extremely strong and tough.”

Using a laser, researchers were able to engrave networks of three-dimensional micro-cracks in borosilicate glass slides – chosen purely for their availability – to create similar weak boundaries. They were able to increase the toughness of the slides by 200 times compared to non-engraved slides.

Engraving networks of micro-cracks in configurations of wavy lines – similar to the edge of a jigsaw puzzle piece – stopped the cracks from propagating and becoming larger. The researchers also filled the cracks with polyurethane, but Barthelat said this is not essential to preventing the glass from shattering.

“What we know now is that we can toughen glass, or other materials, by using patterns of micro-cracks to guide larger cracks, and in the process absorb the energy from an impact,” said Barthelat. “We chose to work with glass because we wanted to work with the archetypal brittle material. But we plan to go on to work with ceramics and polymers in the future.

Overcoming the brittleness of glass through bio-inspiration and microarchitecture