Prestress state evolution during thermal activation of memory effect in concrete beams strengthened with external SMA wi
- PDF / 3,034,512 Bytes
- 15 Pages / 595.276 x 790.866 pts Page_size
- 49 Downloads / 190 Views
(2020) 20:142
ORIGINAL ARTICLE
Prestress state evolution during thermal activation of memory effect in concrete beams strengthened with external SMA wires A. Debska1 · Piotr Gwozdziewicz2 · A. Seruga2 · X. Balandraud3 · J. F. Destrebecq3 Received: 6 May 2020 / Revised: 9 September 2020 / Accepted: 26 September 2020 © The Author(s) 2020
Abstract The memory effect of shape-memory alloys (SMAs) has opened interesting perspectives to create prestress states in concrete elements. However, the procedure has not been yet fully resolved due to the complex thermomechanical behavior of these alloys, in addition to the practical difficulties of mechanical coupling between SMA and concrete elements. The present study deals with tests on the development of prestressing forces in concrete beams during the thermal cycle required in the procedure. Pre-stretched nickel–titanium wires were externally placed on concrete prismatic beams equipped with strain gauges. As concrete rupture may occur during the heating by the Joule effect, a compromise must be found between the SMA pre-stretch level and the maximum temperature to be applied before returning to ambient temperature. A macroscopic model was developed to analyze this compromise. The complex thermomechanical response of SMAs implies a particular attention in the definition of the ambient temperature and heating conditions for the creation of prestress states in concrete components. Keywords Shape memory alloy · Prestressing force · Bending · Civil engineering · Transformation temperature · Nickel– titanium
1 Introduction Shape memory alloys (SMAs) are active materials that have the ability to cancel apparent “plastic” strain by heating, a phenomenon known as the memory effect [1–5]. When the latter is mechanically hindered, the SMA component therefore develops forces, a mechanism that has found many applications in engineering. The underlying physical phenomenon is a solid–solid transition between two phases, namely austenite (A) and martensite (M), triggered by temperature and stress. Roughly, austenite and martensite are present at “high” and “low” temperatures respectively. In the austenite state, a SMA component has a unique memorized shape that was defined during material elaboration. Note that SMAs are mainly supplied in the form of wires, springs, foils, sheets, bars and tubes. The A → M transformation * Piotr Gwozdziewicz [email protected] 1
Aldebud Aleksandra Dębska, 30689 Kraków, Poland
2
Cracow University of Technology, 31155 Kraków, Poland
3
CNRS, SIGMA Clermont, Institut Pascal, Université Clermont Auvergne, 63000 Clermont‑Ferrand, France
can be achieved by cooling or deforming. In the martensite state, a SMA component can be “permanently” deformed by several percent. The recovery of the memorized shape is obtained by heating (activation of the M → A transformation). Note that the Joule effect is easy to use thanks to the metallic nature of SMAs, although heat loss may penalize the amplitude of the temperature increase [6]. The memory e
Data Loading...
