2019 CSCE Annual Conference - Laval (Greater Montreal) Conference
Mr. Rakesh Ranjan, University of Waterloo
Luqman Hakim Ahmad Shah
Mr. Ahmed Rahem, Université du Québec à Chicoutimi
When it comes to vehicular bridges rehabilitation or replacement, designers hardly think of aluminium as a potential structural material. Still, lightweight, corrosion resistance and lower maintenance costs are some assets that aluminium offers compared to steel or concrete. Also, some cases in North America have proved that the retrofit or replacement of an existing bridge deck by one in aluminium is effective, quick and profitable. This factory-built technology is made of extruded aluminium profiles joined by friction stir welding process.
Friction stir welding (FSW) is a solid-state joining process for different kind of metals. Multiple industries use this perfectly adapted welding technology for aluminium alloys, such as aviation, automotive, aerospace and, more recently, construction. Even with higher productivity and better-quality joint obtained with FSW compared to fusion welding process, it is still barely regulated in fatigue and dynamic behaviour design codes for structural applications. Then, this lack of regulations does not encourage designers in using aluminium as bridge element. In order to overcome the current situation, the main goal of this project is to develop improved, 'performance-based' code provisions for the quality control and fatigue design of FSW joints in aluminium bridge decks.
This study includes fatigue characterisation of 6061-T651 FSW joints under constant amplitude and simulated in-service loading conditions. Furthermore, welding defect tolerances will be established for structural applications. Such tolerances exist for fusion welding regulations and even for FSW in aerospace applications (AWS D17.3/D17.3M). So far, studies have shown that excessive flash and kissing bond under 0,3 µm length have an insignificant impact on fatigue life. Exceeding this kissing bond length, failure from crack initiation at the weld root is more likely to happen, which decreases significantly fatigue life. Wormhole defect on 6061-T651 and surface misalignment have not been studied yet. Finally, this study will contribute to develop fatigue criteria and welding defect tolerances in design codes and regulations for FSW which, hopefully, will be promoting aluminium using in civil engineering.