Air-coupled ultrasonic NDE of automotive tires

Evaluating the elastic properties of rubber is important for improving tire performance. Here, new ultrasonic techniques and results are reported for both soft rubber and real tire materials. First, on soft rubber, immersion C-Scan images revealed high attenuation and non-uniform grain size distribution. Through the application of new broadband, high power, high resolution transducers, air-coupled ultrasound succeeded in traveling through the soft rubber showing the efficiency of the new air coupled technique for imaging and evaluation of rubber materials. Secondly, sections of three tires were tested: (1) new, (2) 3 year-20,000 miles, (3) a 5 year-40,000 miles. Each tire section consists of three layers made of different rubber materials, separated by wire mesh. Because of the complexity of the tire's structure and its high attenuation, evaluation of all three layers, but especially the middle layer, is difficult. High power tone-bursts at 1 MHz were applied to a high impedance immersion transducer. Layer reflections could be separated such that the middle layer and the wire belts at the interfaces could be interrogated. This report will detail our new techniques and provide examples for the results obtained.