Quality control and fatigue design of friction stir welded joints in aluminum bridge decks

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Highway authorities in North America are currently faced with significant and pressing bridge maintenance costs. A recent industry report on aluminum use in bridges found light weight decks for new bridges and rehabilitation projects to be an application area with particular promise. A subsequent economic study concluded that: 1) bridge decks are an application where aluminum clearly has a potential for market growth, and 2) friction stir welding (FSW) represents a transformative technology, which could have a significant influence on the durability and economics of aluminum bridge decks. A design code for structural FSW joints does not yet exist in Canada. Existing international codes (e.g. ISO, AWS) include quality control provisions based on "best practice", which have not yet been related to structural performance. This project will be be performed collaboratively by researchers at the University of Waterloo (UW) and Université du Québec à Chicoutimi (UQAC) with the goal of developing improved, "performance-based" code provisions for the quality control (QC) and fatigue design of FSW joints in aluminum bridge decks. To achieve this goal, the following tasks will be performed: 1) specimen preparation and metallurgical analysis; 2) fatigue testing of FSW specimens; 3) statistical and fracture mechanics analysis of FSW test results; and 4) development of improved guidelines for QC and fatigue design of FSW bridge deck joints. A particularly novel aspect of the project will be the plan to fatigue test and analyze welds with varying levels of quality (i.e. various defect types with varying degrees of severity). This project will make a significant contribution to the current state-of-knowledge, which will move the Canadian industry and researchers working on FSW to the leading edge of this field, through the new knowledge acquired and the transformation of this knowledge into design recommendations.