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ISRN Materials Science
Volume 2013 (2013), Article ID 320370, 4 pages
http://dx.doi.org/10.1155/2013/320370
Research Article

Behaviour of NiTi SMA Helical Springs under Different Temperatures and Deflections

1Defence Research and Development Laboratory, Hyderabad 500 058, India
2Department of Applied Mechanics, IIT Madras, Chennai 600 036, India

Received 21 May 2013; Accepted 11 June 2013

Academic Editors: Y. Ge, K. Hokamoto, V. Ji, and P. Karjalainen

Copyright © 2013 R. Santhanam et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Shape memory alloys (SMAs) are one of the most widely used smart materials in many applications because of their shape memory effect property. In this work, the behaviour of NiTi SMA helical spring was evaluated through isothermal force-displacement experiment (IFDE) and shape recovery force experiment (SRFE). The transformation temperatures of SMA spring were determined by differential scanning calorimetry (DSC) test. In situ heating of SMA spring by direct electric current was used instead of conventional furnace heating. The continuous measurement of temperature of SMA spring during heating and cooling was ensured with attaching the thermocouple by heat shrinkable sleeve. From IFDE, the force-deflection behaviour under different constant temperatures and from SRFE and the force-temperature behaviour under different constant deflections are obtained. The results of IFDE show that the force increases and the residual displacement decreases with an increase in the temperature, and the stiffness of the spring at austenite state is greater than that at martensitic state. The results of SRFE show that the shape recovery force increases more or less linearly with an increase in the initial deflection for the same temperature range. But the shape recovery forces are not similar during heating and cooling stages. This paper presents the experimental setup, experimental procedures, and the observed behaviour of SMA helical springs under different temperatures and deflections.