Fatigue Tests on Fe-SMA Strengthened Steel Plates Considering Thermal Effects

An iron-based shape memory alloy (Fe-SMA) can be used to conveniently apply prestress strengthening via a heating and cooling procedure. Material-level tests demonstrated that prestress of Fe-SMAs is sensitive to mechanical and thermal loading. Durability of steel structures strengthened by Fe-SMAs when subjected to harsh service conditions, such as coupled thermomechanical cycles is not fully understood. In this study, high-cycle fatigue tests were conducted on damaged steel plates retrofitted with Fe-SMA strips. Four temperature scenarios were adopted: room temperature (RT), a low temperature (LT) of -20 degrees C, a high temperature (HT) of 60 degrees C, and a cyclic temperature (CT) from -20 degrees C to 60 degrees C. Results showed that regardless of temperature variation, the Fe-SMA presented reliable repairing effects on steel plates, of which, the fatigue life was 2.1-3.5 times larger than that of the unstrengthened samples. The difference in coefficients of thermal expansion (CTEs) between the Fe-SMA and steel, as well as loss of prestress of the Fe-SMA due to fatigue and thermal loading, both affected the fatigue performance of the retrofitted specimens.