New Kind of Blast-Resistant Glass

[Elmore Furth]

With the huge edifices of glass that modern buildings present, blast resistant glass has real significance.

(Dec. 27, 2010) — Whether in a hurricane, tornado, or bomb attack, a leading cause of injury and death is often fast-flying shards of glass. Explosions and high winds can cause windows in buildings to shatter-spewing jagged pieces of glass in every direction.

Unlike today's blast-resistant windows which are made of pure polymer layers, this new design is a plastic composite that has an interlayer of polymer reinforced with glass fibers-and it's only a quarter-inch thick.

The project team recently subjected their new glass pane to a small explosion. "The results were fantastic," exclaimed Sanjeev Khanna, the project's principal investigator and an associate professor of mechanical engineering at Missouri. "While the discharge left the pane cracked, the front surface remained completely intact."

The secret to the design's success is long glass fibers in the form of a woven cloth soaked with liquid plastic and bonded with adhesive. The pane is a layer of glass-reinforced clear plastic between two slim sheets of glass. Even the glue that holds it all together is clear. Think of it as a sandwich: the slim sheets of glass are the two slices of break; the liquid plastic and long glass fibers make up the crunchy peanut butter in the middle.

The glass fibers are typically 15 to 25 micrometers in diameter, about half the thickness of a typical human hair. The small size results in fewer defects and a decreased chance of cracking. The strong glass fibers also provide a significant reinforcing effect to the polymer matrix used to bind the fibers together. The more fibers used, the stronger the glass reinforcement. And while traditional blast-proof glass usually has a greenish ting, special engineering renders the polymer resin transparent to visible light.

Engineers expect the new design will be comparable in cost to current blast-proof glass panes, but lighter in weight. At only a quarter-inch thick, this newly engineered composite would slip into standard commercial window frames, making it much more practical and cost-efficient to install.

The goal is to create blast-resistant panes as large as 48 by 66 inches-the standard General Services Administration window size for qualification blast testing-that can still be cost-effective. While dependent on results from upcoming tests, Khanna hopes this glass could become commercially available in three to four years.

New Kind of Blast-Resistant Glass