Description
Iron based shape memory alloys (SMAs) attracted considerable attention in recent years, especially with respect to potential applications in civil engineering. The inherent shape memory phenomena like superelasticity and the shape memory effect (SME) offer great opportunities for use as damping, coupling or prestressing elements. Considering the SME, a deformation initially remains after unloading and the shape recovery can be initiated by subsequent heating. If the shape recovery is constrained during heating, e.g. by a firm anchorage to another structure, a considerable mechanical stress builds up. In the field of civil engineering, this effect can be used to reinforce concrete structures by prestressing with shape memory alloy elements. In contrast to traditional prestressing technologies using high strength steels, the use of SMAs opens up new design opportunities and simplifies retrofitting of existing buildings. Fe-Mn-Al-Ni SMAs are one of the most promising SMAs for the envisaged application. The present study shows the prestressing potential of the alloy and the influence of different process parameters. Due to the growth of nanosized precipitates in the same temperature regime required for activation of shape recovery (150°C-300°C) the prestress level can be tailored as a function of both, maximum heating temperature and dwell time. This also includes the possibility of subsequent increase of prestress level during service life.
