Detection of weak bonding in friction welds by ultrasound

Weak bonding defects, which are special defects occurring in solid-state welded joints, are very dangerous. These defect cannot be detected effectively with normal ultrasonic testing methods used in industry, because the signal reflected from such a defect is so weak that may be overshadowed by the scattering noise from surrounding materials. In this paper, a simple model for an ultrasonic non-destructive testing of friction-welded joints, which contain joints with weak bonding defects and without any welded defect, is proposed. According to the model, it is found that the amplitude-frequency characteristic of the ultrasonic signals of the joints with various qualities is apparently different. According to the information provided by the model on the ultrasonic signals, an algorithm based on the wavelet transform is proposed. Experimental data for the friction-welded specimens show encouraging defect detection capabilities from the use of the algorithm. (C) 1998 Elsevier Science B.V.