Ultrasonic testing for friction welded joints in low carbon steel with weak bonding

In this paper, ultrasonic non-destructive testing to detect weak bonding of friction-welded joints is discussed. A modern spectrum analysis using autoregressive (AR) power spectra is used to recognise the various defects causing weak bonding, such as lack of fusion and grey speck. The defects discussed in this paper are very difficult to detect using conventional ultrasonic testing methods on friction-welded joints. The results show that the weak bonding defects cannot be detected in the time domain. Characteristics obtained from the frequency domain of the AR power spectrum, however, are useful to detect the various weak bonding defects, and the area of the defects can be indicated by a characteristic value obtained from the frequency spectrum.