Engineers inspired by the mother-of-pearl lining of mollusk shells have found that etching wavy lines in glass can actually give the brittle material the ability to bend and dent instead of shatter.
“Mollusk shells are made up of about 95 percent chalk, which is very brittle in its pure form,” says François Barthelat of the mechanical engineering department at McGill University. “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, which is why people have been studying its structure for the past twenty years.”
Previous attempts to recreate the structures of nacre have proved to be challenging.
“Imagine trying to build a Lego wall with microscopic building blocks. It’s not the easiest thing in the world.”
Instead, what Barthelat and his team chose to do was to study the internal ‘weak’ boundaries or edges to be found in natural materials like nacre and then use lasers to engrave networks of 3D micro-cracks in glass slides in order to create similar weak boundaries. The results were dramatic. Their research is published in Nature Communications.
The researchers were able to increase the toughness of glass microscope slides 200 times compared to non-engraved slides. By engraving networks of micro-cracks in configurations of wavy lines in shapes similar to the wavy edges of pieces in a jigsaw puzzle in the surface of borosilicate glass, they were able to stop the cracks from propagating and becoming larger.
They then filled these micro-cracks with polyurethane. This second process is not essential since the patterns of micro-cracks in themselves are sufficient to stop the glass from shattering, according to Barthelat.
“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,” says 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 future. Observing the natural world can clearly lead to improved man-made designs.”
The authors acknowledge useful technical advice by the company Vitro.
The Natural Sciences and Engineering Research Council of Canada and the Canada Foundation for Innovation funded the study, with partial support for one of the authors from a McGill Engineering Doctoral Award.
Source: McGill University