Scenarios for repairing FSW joints that had turned out to be defective were developed in the present study. Lack of penetration, offset and tunnel defects were intentionally produced in FSW butt joints and full-length re-welding of the complete joint line as well as resulting change in mechanical behaviour was examined. Defective and repaired FSW joints were checked by high frequency ultrasonics and electrical conductivity measurements through the eddy current technique. Mechanical behaviour was characterised in terms of bending, tensile and S-N tests. The evaluation of ultrasonic C- (intensity of reflected signal) and D-scans (time of flight or depth information) was combined. Only by this way, the original defective condition could be distinguished from the repaired configuration in every case. When evaluating electrical conductivity measurements, a small repair effect was registered. But observed changes in electrical conductivity had essentially microstructural reasons. FSW joints that have turned out to be defective could be repaired by a single re-welding process in either case. A second re-welding was not observed to generate any kind of improvement. Conversely, it slightly reduced strength, ductility and fatigue life. As compared to 2024, 2198 showed relatively low weld efficiencies. Furthermore, 2198 needed a perfect surface finish when fatigue loaded, as the very thin TMAZ on advancing side was prone to fatigue crack initiation. With respect to the generation of weld defects due to non-optimum weld parameters, 6156-T6 was the most critical alloy, whereas 2198-T8 was the most fault-tolerant material. 2024-T3 took a medial position. With respect to mechanical properties of the repaired condition, 6156-T6 was likewise the most critical alloy, whereas 2024-T3 was quite insenstive to additional repair thermal cycles. In this case, 2198-T8 took a medial position.
Repair of defective FSW butt joints
2010
15 Seiten, 10 Bilder, 1 Tabelle, 10 Quellen
Conference paper
English
Development of rail butt welding and study of butt-welded rail joints
Engineering Index Backfile | 1935
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