What a glass: Tough enough for hurricanes

MU professor’s glass is thinner, cheaper and stronger.
Friday, September 19, 2003 | 12:00 a.m. CDT; updated 7:20 p.m. CDT, Tuesday, July 15, 2008

As the heavy rain and 95-mph winds of Hurricane Isabel churned toward the East Coast, many residents in the storm’s path took the time-honored precaution of reinforcing windows and glass doors with tape.

Such measures may not be necessary in the future. An MU researcher is developing a type of glass that could reduce the property damage and physical injuries caused by tropical storms and hurricanes.

The glass, created by Sanjeev Khanna, associate professor of mechanical and aerospace engineering, is created by replacing the plastic used in conventional laminated glass with a layer of polymer reinforced with glass fibers. The polymer layer is then sandwiched between heat-treated glass. Not only is the new glass three or four times stronger than conventional glass, Khanna said, it is also thinner by about 30 percent and less expensive.

Khanna has tested the impact resistance of both types of glass by shooting 4-inch-long, 1/2-inch diameter steel rods at them at 60 miles per hour. Khanna believes the results suggest the polymer-reinforced glass could withstand a Category 3 hurricane, which produces winds as high as 120 mph.

“The standard glass broke on the first shot,” Khanna said. “Ours broke on the sixth.”

But impact resistance is only one factor Khanna has to consider. Changes in atmospheric pressure caused by a hurricane’s rotating winds put enormous stress on glass.

“A window is subjected to a vacuum where it is being sucked, then (when pressure changes) it is pushed,” he said. “Debris can cause a crack, and fluctuations in pressure can enhance cracking.”

To address the problem, Khanna is creating a computer-controlled hurricane simulator. The test glass will be slightly damaged by a projectile, then placed in the simulator to see how the hurricane forces affect it. The simulator should be up and running within a month. Khanna said he hopes to see his hurricane-resistant glass on the market in two to three years.

Khanna received a grant from the National Science Foundation during the 2000 hurricane season to develop the glass. His academic curiosity and background in composite materials also pushed him toward the project as did his personal experience with bad weather in 1991.

“I lived in Rhode Island during Hurricane Bob,” he said. “I saw the destruction firsthand.”

Khanna says that while it is hard to quantify how much his glass could reduce hurricane damage, it will be a great step forward.

“Right now people are using cardboard and wood (to protect their windows),” he said. “Suppose they would not have to do that? It can save time, money and emotional distress.”

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