Dissimilar friction welding of NiTi shape memory alloy and steel reinforcing bars for seismic performance

Integration of NiTi superelastic bars with steel reinforcing bars is a promising path for increasing the seismic performance of reinforced concrete structures. Welding of NiTi alloy to steel is however not straightforward with standard welding techniques. Friction welding is investigated for performing this dissimilar junction using both regular friction (forced controlled) and milling (position-controlled) machines. When adequate shortenings and forging forces are selected, the welds can withstand the tensile strength of the steel rebars. Failure actually occurs in the heat-affected zone of the steel bars. The intermetallic (IM) layer at the welded interface should be kept thin and cracks should be limited in the steel layer next to the interface in order to avoid early brittle interfacial cracking.