Fatigue Strengthening of Metallic Structures with a Thermally Activated Shape Memory Alloy Fiber-Reinforced Polymer Patch

This paper evaluates the effectiveness of a new type of shape memory alloy (SMA)/fiber-reinforced polymer (FRP) patch for repair of fatigue-sensitive steel elements. Twenty-seven single edge-notched steel coupons with different configurations of reinforcement were tested under tension-tension fatigue loading at three different stress ranges up to failure. Test results indicated that the coupons that were reinforced with the SMA/carbon FRP (CFRP) composite exhibited average fatigue lives that were 26.4 and 15.3 times those of the unreinforced coupons at stress ranges of 155 and 217MPa, respectively. In comparison, coupons that were reinforced with CFRP only and those reinforced with only SMA wires exhibited average fatigue lives that were 8 and 1.7times those of the unreinforced coupons, respectively, at a stress range of 155MPa. This suggests that there is a synergistic effect between the prestressing forces provided by the SMA wires and the crack bridging provided by the CFRP. The results indicate that these SMA/FRP patches are a promising technology for rehabilitation of fatigue-sensitive steel structures. (C) 2016 American Society of Civil Engineers.