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Scientists develop “bendy” glass

Jan. 31, 2014
Courtesy of McGill University
and World Science staff

Nor­mally when you drop a glass on the floor it shat­ters. But in the fu­ture, thanks to a new tech­nique, when the same thing hap­pens the glass might just bend and be­come slightly de­formed.

Re­search­er François Barthe­lat and col­leagues at McGill Uni­vers­ity in Can­a­da took in­spira­t­ion from nat­u­ral struc­tures like seashells in or­der to boost the tough­ness of glass.

“Mol­lusk shells are made up of about 95 per cent 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,” he added. It’s “known to be ex­tremely strong and tough, which is why peo­ple have been stu­dy­ing its struc­ture for the past 20 years.”

Pre­vi­ous at­tempts to c­re­ate na­cre-like struc­tures have run in­to dif­fi­cul­ties, Bar­the­lat said. “Imag­ine try­ing to build a Lego wall with mi­cro­scop­ic build­ing blocks. It’s not the eas­i­est thing in the world.” 

In­stead, he and his team studied in­ter­nal ‘weak’ bound­aries or edges found in ma­te­ri­als like na­cre, then used lasers to en­grave net­works of micro-cracks in glass slides to cre­ate si­m­i­lar weak bound­aries. Per­haps sur­pris­ingly, these tough­en the glass by absorb­ing energy from an im­pact.

The sci­en­tists said they were able to in­crease the tough­ness of glass slides (the kind of glass rect­an­gles that get put un­der mi­cro­scopes) by 200 times. 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 the glass, they were able to stop the cracks from prop­a­gat­ing and be­com­ing larg­er. 

They then filled these micro-cracks with pol­y­u­re­thane, al­though ac­cord­ing to Barthe­lat, this sec­ond pro­cess is not es­sen­tial since the pat­terns of micro-cracks in them­selves are suf­fi­cient to stop the glass from shat­ter­ing.

The re­search­ers worked with glass slides simply be­cause they were ac­ces­si­ble, but Barthe­lat be­lieves that the pro­cess will be very easy to scale up to any size of glass sheet, since peo­ple are al­ready en­grav­ing log­os and pat­terns on glass pan­els.

“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 fu­ture.”


The findings were pub­lished Jan. 28 in the jour­nal Na­ture Com­muni­cations

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Normally when you drop a glass on the floor it shatters. But, in future, thanks to a new technique, when the same thing happens the glass might just bend and become slightly deformed, scientists say. Researcher François Barthelat and colleagues at McGill University in Canada took inspiration from natural structures like seashells in order to boost the toughness of glass. “Mollusk shells are made up of about 95 per cent 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, which is why people have been studying its structure for the past twenty years.” Previous attempts to recreate the nacre-like structures have run into difficulties, Barthelat said. “Imagine trying to build a Lego wall with microscopic building blocks. It’s not the easiest thing in the world.” Instead, what he 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 micro-cracks in glass slides in order to create similar weak boundaries. The scientists said they were able to increase the toughness of glass slides (the kind of glass rectangles that get put under microscopes) by 200 times. 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 the glass, they were able to stop the cracks from propagating and becoming larger. They then filled these micro-cracks with polyurethane, although according to Barthelat, this second process is not essential since the patterns of micro-cracks in themselves are sufficient to stop the glass from shattering. The researchers worked with glass slides simply because they were accessible, but Barthelat believes that the process will be very easy to scale up to any size of glass sheet, since people are already engraving logos and patterns on glass panels. He and his team are excited about the work that lies ahead for them. “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 future. Observing the natural world can clearly lead to improved man-made designs.”