Non-destructive detection of lack of penetration defects in friction stir welds

This study focuses on the comparative investigation of different non-destructive inspection (NDI) techniques for detecting the lack of penetration discontinuities in butt joint friction stir (FS) welds. A variably sized lack of penetration has been introduced purposely by progressively changing the tool pin's length. While inspecting the weld from the discontinuity side provides results of higher sensitivity, service inspection of the FS welded components requires evaluation of the welding tool's side, opposite the defect containing one. Non-destructive techniques amenable for inspection from either the tool side or the far side of the weld are analysed, and results from inspection are presented for comparison. Subsequently, bending tests and metallographic examinations were employed to confirm the size of the lack of penetration defects and correlate these results with the NDI capabilities.