CHAMPAIGN, Ill. -- Researchers at the University of Illinois have developed a fast, low-cost inspection system for evaluating the structural integrity of new and used steel-belted-radial truck tires. The instrument uses ultrasonic sound waves to detect ply delaminations, weakened, damaged or broken cords and other, potentially dangerous, hidden defects.
"Driving on underinflated radial truck tires can damage the steel cords in the sidewalls," said Henrique Reis, a professor of general engineering. "Overflexing of the tire may cause the steel cords to break, fray or delaminate, weakening the sidewall. When the tire is serviced, these weakened areas can rupture, releasing a high-pressure blast of air that can cause serious injury or death."
To inspect for hidden damage, Reis and graduate student Paul Golko use an analytical, nondestructive evaluation technique called acousto-ultrasonics. First, the researchers use an ultrasonic transducer to inject a sound wave into the side of the tire. The ultrasonic pulse then propagates along the sidewall, where it is picked up by another transducer and analyzed by a computer.
"Tires are scanned with measurements recorded every 0.3 degree of tire rotation, for a total of 1,200 samples," Reis said. "This angular sampling interval was chosen because it is smaller than the spacing between radial cords on the tire at the transducer locations. Therefore, we can test for damage in each individual cord. The entire measurement process takes less than a minute per tire."
By analyzing the attenuation characteristics of the transmitted signals, the researchers can evaluate and characterize damage within the tire.
"We can detect strained or damaged cords because the sound wave is not transmitted as efficiently as in a normal steel cord," Reis said. "The greater the damage, the higher the signal attenuation. If the signal disappears, the cord is broken. By studying the signals, we also can detect areas where the steel cords and rubber have separated."
A color-coded display shows not only regions of broken or damaged cords, but also areas where the steel cords are weakened to the point where the tire should be removed from service. By evaluating the residual strength in the sidewalls, the instrument can determine both a tire's remaining useful life and whether it is worth retreading.
"A typical used-tire casing may contain numerous defects by the time it is retreaded," Reis said. "To reduce the number of retreads that fail prematurely, all tire casings should be inspected for damage prior to retreading. For safety reasons, we don't want to use bad tires; but, for economic and ecological reasons, we don't want to throw away good tires that can be retreaded. This instrument enables us to easily distinguish between the two."
Reis and Golko will describe the new inspection system in a future issue
of Tire Science and Technology.