Enough enemy bullets have flown through the windshields of US military vehicles for researchers to decide it’s time for a truly tough transparent surface. In a study conducted at MIT, materials scientist Christine Ortiz is researching the amazing ability of the windowpane oyster’s shell to both achieve 80% transparency and still handle significant impacts without shattering. “We have long studied natural exoskeletons as inspiration for the development of advanced engineered protective systems” Ortiz said.
An up-close view of the windowpane oyster’s shell shows how little the damage radiates from an impact point. (Ling Li/MIT)
What confused scientists studying the windowpane oyster was how its shell was able to absorb impact so well despite consisting mostly of calcite. This is the same main component that makes up relatively brittle materials like limestone and chalk. To figure it out, they had to take their observations down to the nanometer – that’s one billionth of a meter. What they found via this super close look was that the surface of the shell was organized into many layers of long diamond shaped calcite crystals. When scientists intentionally dented the shell with a diamond tipped probe, the surface naturally absorbed the impact by reorienting the layered crystals to form a small crater that kept damage to an impressively small area.
Below is a video from NewScientist demonstrating how much easier calcite falls apart then the largely calcite-composed oyster shells.
This doesn’t mean we’re going to start replacing Hummer windshields with oyster shells, but it could mean a totally new way of approaching clear protective surfaces. Right now the most durable clear shields and visors are made from laminated glass. These surfaces can sometimes stop a single bullet, but because the resulting fractures can spread so wide, it makes the whole structure super vulnerable to a second impact. This is less than desirable since single-shot rifles probably aren’t coming back to the front lines anytime soon. Because the damage done to the oyster shell structure remains so localized, it means that somebody could theoretically go full-Tony Montana on a similarly structured windshield without harming those behind it.
HT: New Scientist