Title: A new simple formulation for instantaneous coil diameter of a SMA helical spring

Authors: R. Santhanam; Srinivasan M. Sivakumar; Y. Krishna

Addresses: Aerospace Structures Division, Defence Research and Development Laboratory, Hyderabad, India ' Department of Applied Mechanics, IIT Madras, Chennai, India ' Aerospace Structures and Thermal Group, Defence Research and Development Laboratory, Hyderabad, India

Abstract: Helical coil tension springs made of shape memory alloy (SMA) materials generally undergo large deflection under loading during which their mean coil diameter changes noticeably. In the design of these helical coil springs, it is necessary to identify the real behaviour which may be affected by the variation in actual coil diameter. Therefore, a simple formulation is proposed in this paper for predicting instantaneous coil diameter. The predictions from present formulation match very closely with experimental measurements. The proposed formulation is relatively easy to adopt for design calculations. The effects of varying coil diameter on the spring characteristics are also discussed. This is very general and can be used for any helical spring which undergoes small or large deflections, although the proposed formulation is derived for SMA helical spring.

Keywords: shape memory alloy; SMA; helical coil tension springs; instantaneous coil diameter; large deflection.

DOI: 10.1504/IJMSI.2020.107297

International Journal of Materials and Structural Integrity, 2020 Vol.14 No.1, pp.22 - 32

Received: 10 Aug 2018
Accepted: 25 Mar 2019
Published online: 12 May 2020 *