Application of air – coupled ultrasonic technique for sizing of delamination type defect in multilayered materials

Ultrasonic testing using couplants is most popular technique for non destructive testing of solid materials. In the most non – destructive evaluation tasks such as investigation of materials whose properties may be changed by liquid contact this technique can not be used. Use of contact technique can be restricted for complex geometry structures. Also, liquid couplants cannot be used when materials under investigation are hot, or when water can fill defects and the detectability of the defects may be reduced. Air – coupled ultrasonic technique is very attractive for non destructive testing and evaluation, because it avoids the disadvantages caused by liquid couplants. Many authors present results of air–coupled ultrasonic investigation of solid materials [1 – 7], but mostly it is qualitative evaluation. Objective of this work was to check possibility to use air coupled ultrasonic technique to measure the dimensions of defects in aluminum and carbon fiber reinforced plastic multilayered structures.