AS WE’VE seen recently, NASCAR collisions result in debris flying everywhere. Wheel tethers and other safety hardware can do only so much. Even minor on-track debris can cause windshield damage.
Several of these cars are not traveling the customary line.
At the upcoming SAE 2013 World Congress, April 16-18 in Detroit, researchers from NASCAR will describe investigations that resulted in this year’s new windshield regulations.
SAE’s Automotive Engineering International magazine, March 5, 2013, gave a preview, a summary of which I offer here.
From 2000 through 2012, windshields of NASCAR cars and trucks were required to be hard-coated monolithic polycarbonate. These windshields provided the baseline for the researchers’ evaluations. Also tested was a prototype laminated counterpart, two layers of polycarbonate separated by urethane. All windshields had a single layer of Mylar tear-off applied. All were aligned at 37 degrees from horizontal.
Errant beverage cans being a recognized hazard, these were the first projectiles tested. Full aluminum cans were propelled by air pressure at windshields. Impact speeds were typical of those in NASCAR racing, 200 mph. (For non-racing types, note this is almost a football field traveled in each second.)
Hardly aerodynamic, the cans were found to tumble significantly prior to impact. Within a millisecond of contact with the windshield, the can would rupture. None of the aluminum fragments—nor the can’s contents—made it through any test windshield. However, the baseline monolithic polycarbonate windshields suffered fractures in all tests.
Even more challenging are vehicle-related debris, pieces of brake rotor and the like. To simulate this, researchers used solid steel slugs, 1.25-in. diameter and 2.5-in. long. Each weighed a little less than 1 lb. and was projected against the test windshield at 200 mph.
Seen at the instant of impact: A steel test projectile pierces the monolithic windshield, left, but not the laminated counterpart, right. Image from SAE International.
The projectiles passed through monolithic windshields, but not the laminated ones. High-speed video showed that—after piercing the monolithic windshield—the steel projectile was still traveling 110 ft./sec. Even though its kinetic energy was reduced by more than seven times, it was still a projectile within the race car.
On the basis of these results, laminated windshields are being implemented for all 2013 NASCAR vehicles.
Some other interesting details of this: Another option of merely increasing the thickness of monolithic material had detrimental tradeoffs. Acceptable optical quality was more difficult to achieve with a thicker material. And the component’s weight increased significantly—thus complicating windshield retention in accidents.
Also, NASCAR Track Services checked that the laminated windshields would be compatible with their extraction procedures and equipment.
Good solid R&D here, and the result is safer motorsports. ds
© Dennis Simanaitis, SimanaitisSays.com, 2013