Stress recovery behavior of a promising NiTiNb-SMA plate for bonded prestressed strengthening

Abstract

Shape memory alloys (SMAs) are functional metallic materials, possessing a remarkable characteristic known as the shape memory effect (SME), by which a considerable recovery stress can be generated through a simple thermal activation. A NiTiNb-SMA plate is employed in this study, aimed at prestressed strengthening of steel members. To better understand the mechanism of the generation of recovery stress, tests were conducted on the NiTiNb-SMA plates (thickness 1.5 mm) to characterize the basic mechanical properties and stress recovery behavior. Tests include: tensile failure test, prestraining, activation, and re-activation. The influence of key parameters such as prestrain level and activation temperature on the stress recovery behavior of this NiTiNb-SMA plate was evaluated. Re-activation was discussed. Test results revealed that the largest recovery stress reached 448.6 MPa when the material was prestrained by 8% and activated at 180℃. This suggests that the activation temperature of 180℃ could be optimal for this material to generate sufficient recovery stress. Such a strategy should be promising for bonded prestressed strengthening, as this activation temperature would have limited influence on the adhesive bond of the bonded prestressed strengthening system.