Study Of Ultrasonic NDT Characteristics For Cu/Steel Inertia Friction Welded Joints

In the present work the ultrasonic nondestructive testing (NDT) characteristics of friction welded dissimilar materials joints have been systematically studied. The specimen tested is the Cu-steel inertia friction welded joints. In the testing a US PAC company made ultrasonic C scan system with focus transducer is used in water immersion. First, effect of test parameters on the C scan characteristics is investigated for the welded joints. In the meantime supersonic A signals are recorded for the special interesting regions. Then, micro samples are sectioned. Using micro shear testing local mechanical properties of the joints are determined.Through the analysis of the supersonic C scan images, gray scale of the image is classified. Based on the relation between the ultrasonic reflection amplitude and the micro shear properties, it is indicated that the maximum shear strength is decreased with increasing the reflective amplitude. In addition the specific area of different gray scale region in the C scan images can be correlated to the calculated strength of the joints. It is felt that the estimate of the strength of joints is coincident with the welding parameters. Thus, the gray scale of the C scan images may be used to characterize the joint quality.For the region where the relation between the signal reflection and micro shear strength can not be well correlated further signal processing technique is used. By means of Fourier's transformation, the micro shear toughness of the joints can be evaluated through the characteristic analysis in frequency domain. Considering effect of noise on the available signals, wavelet transformation is utilized to decrease the noise in the reflective signals. It is indicated that the signal-noise ration (SNR) may be increased to a certain extent. This offers a foundation for application of wavelet transformation technique to analyze the quality of friction welded joints.