SMA Types for Non-mechanical Stressing Structural Applications

Over the past few years, research on the use of shape memory alloys (SMAs) in prestressing concrete buildings has produced encouraging results. One SMA that has shown potential for prestressing applications is NiTiNb. The thermomechanical behavior of thermally prestressed NiTiNb SMA under loading and temperature conditions relevant to civil structural applications is presented in this chapter. The recovery stress of prestrained wires and the monotonic and cyclic behaviors of thermally prestressed wires are investigated in a testing program on NiTiNb wires under varied testing durations and ambient temperatures. A study on the potential impact of severe corrosive environments relevant to civil structures on the mechanical behavior of prestressed NiTiNb SMA is also provided. In order to replicate real-world field conditions, the study subjects NiTiNb specimens to wet-dry cycles in NaCl solution using an accelerated aging testing procedure. Specimens made of carbon steel are also evaluated for comparison. The chapter also sheds light on a new Fe-based alloy (FeNiCoTi) that showed promise for prestressing applications. One advantage of using FeNiCoTi alloy is its cost-effectiveness compared to commonly studied NiTi alloy. Differential Scanning Calorimetry (DSC) tests are carried out to investigate the transformation temperatures of FeNiCoTi alloy under different heat treatment methods and prestrain schemes. In addition, cyclic experiments are performed to investigate the FeNiCoTi alloy’s cyclic behavior following stress recovery. Thermal cycle tests are also performed on the FeNiCoTi alloy to understand better how temperature variation affects recovery stress.