Use of tangential radiography and resonance ultrasonic techniques to evaluate bonding quality

Bonding is a useful thermomechanical assembling process allowing a perfect cohesion between two axisymetrical cylinders made of different materials. A perfect knowledge of the quality of the assembly (quantification of mechanical strength or detection of gap between the two parts) is an important step of the manufacturing process. The control that has been developed is performed with two non destructive techniques. First, an ultrasonic method based on the resonance frequency and the electrical impedance measurement of a special piezo-electric transducer placed on the specimen is performed. The shift of the resonance frequency is directly related to the quality of the bonding, and particularly to the strength cohesion between the two parts. When the frequency value points out disbonding area characterized by a gap between the two cylinders, tangential microfocus radiography is performed to evaluate in an accurate way the nocivity of the flaw and particularly the width of the gap. These two complementary techniques have been evaluated and validated by using standard devices, with the same thickness, shape and nature than the real specimen. For the ultrasonic technique, first results show that it is possible to quantify very precisely the quality of the bonding, ranging from a perfect assembly characterized by a high strength between the two cylinders to a partial disbonding area. Small gaps of less than 50/G μm (G magnification) have been evaluated with microfocus radiography. (author)