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An Experimental Study of Discontinuities in Friction Stir Welded Joints through Nondestructive Testing

Friction stir welding (FSW) is a solid state metal joining process. The discontinuities and anomalies encountered in this type of welded joint differ from those of a conventional fusion weld. The discontinuities present in FSW are oriented in a different direction due to the unique formation process involved and are dispersed over the welded region widthwise as well as thicknesswise. The process of detection, evaluation, and characterization of these discontinuities is a challenging aspect, as no specific area is identified as a probable zone of discontinuities. In this study, typical discontinuities that are encountered during the FSW process were intentionally induced and then subjected to different types of nondestructive investigation. The methods and techniques adopted were liquid penetrant testing, radiographic testing, ultrasonic testing, and eddy current testing. The interaction of these discontinuities and study of their response to different nondestructive testing (NDT) methods/techniques are presented in this paper. The eddy current technique appears to be most effective and simple NDT tool for identifying most of the discontinuities. However, a combination with other methods such as radiography is helpful in characterizing these discontinuities.


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