Iron-based shape memory alloy strips for strengthening RC members: Material behavior and characterization

Abstract

Shape memory alloys (SMAs), in the form of bars and strips, can be used as prestressing elements in new reinforced concrete (RC) members or for strengthening existing RC structures, owing to their special characteristic known as the shape memory effect (SME). When the SME comes into play, the material returns to its initial shape upon heating after having been deformed at ambient temperatures. If a return to the initial shape is prevented by mechanical fixation, stress develops in the SMA. A cost-effective iron-based SMA (Fe-SMA) has been developed for application in civil engineering structures. The composition of the developed alloy is Fe-17Mn-5Si-10Cr-4Ni-1(V,C) (mass%). This Fe-SMA exhibits high tensile strength, excellent shape recovery stress (prestress force), and high elastic stiffness. Moreover, its material cost is low and it is easier to manufacture than nickel-titanium (NiTi) alloys. Recently, Fe-SMA strip production has been started at an industrial scale. In this study, the experimentally determined properties of such industrially produced Fe-SMA strips are presented, and their recovery stress and recovery strain have been measured. The effects of prestraining and maximum heating temperature on the obtained recovery stress have been studied. These Fe-SMA strips can be used as external end-fixed reinforcements to strengthen RC structures.

Selbstvorspannende ultrahochfeste Betonelemente

“…Die beiden Phasen sind in Bild dargestellt. Eine Materialcharakterisierung der an der EMPA entwickelten eisenbasierten Formgedächtnislegierung FE‐17Mn‐5Si‐10Cr‐4Ni‐1(V,C) (mass %) wurde in durchgeführt. Das Ermüdungsverhalten dieser Legierung wurde in untersucht.…”

“… Schematisches Verhalten der Einweg‐FGL: (a) mechanisches Vordehnen; (b) Erwärmung der vorgedehnten FGL mit freier Verformbarkeit; (c) Erwärmung der vorgedehnten FGL mit freier Verformbarkeit, Schematic behavior of one way shape‐memory alloy: (a) mechanical pre‐straining; (b) thermal activation of the pre‐strained SMA with free deformation; (c) thermal activation of the pre‐strained SMA with restrained deformation, …”

“…Im Fokus dieser Veröffentlichung stehen die Überprüfung der Machbarkeit des Selbstvorspannungseffektes und die Untersuchung des Einflusses von unterschiedlichen Nachbehandlungsvarianten auf die Kombination der beiden verwendeten Materialien. Eine Materialcharakterisierung kann wie in durchgeführt werden. Aus den Ergebnissen von eigenen Tastversuchen wurden Materialkennwerte rückgerechnet.…”

“…Auch Stützen wurden bereits mit Formgedächtnislegierungen umschnürt und damit aktiv in ihrer Querdehnung behindert. Dies wurde in [33,34] [41,44] Schematic behavior of one way shape-memory alloy: (a) mechanical pre-straining; (b) thermal activation of the pre-strained SMA with free deformation; (c) thermal activation of the pre-strained SMA with restrained deformation, [41,44] B. Kromoser, E. Strieder, J. Kirnbauer: Self post-tensioning ultra-high performance concrete elements…”

Evaluation of Seismic Response of Concrete Structures Reinforced by Shape Memory Alloys (Technical Note)

“…Shape memory alloys (SMAs) are new smart materials that can resist large nonlinear deformations and return back to the original geometry after unloading which made them an appropriate choice for reducing the maintenance costs [8]. In the past decades, many researchers have evaluated the possibility of using SMAs for the structural applications such as dampers [9][10][11], reinforcements [12][13][14][15][16][17], bracing [18,19], seismic isolation systems [20][21][22] and actuators [23,24].…”