Performance Evaluation of Shape Memory Alloy (SMA) Helical Coil: Influence of Mandrel Size and Wire Diameter

Shape memory alloy (SMA) helical coil has a small form factor and high energy density, making them a potential candidate for use as an artificial muscle in endoskeleton suits and walking assists. This paper aims to study the performance of the SMA helical coil geometries across different mandrel sizes (1.0mm, 1.5mm, 2.0mm, 2.5mm and 3.0mm) and wire diameters (0.3mm, 0.5mm and 1.0mm). To achieve this, a winding and heat treatment tool is proposed to create various mandrel sizes across different wire diameters. The evaluated performance parameters include generated force, resistive force and the response time during the transition between austenitic to martensitic phases. The study utilizes a test rig that includes a thermal camera and a load cell. The findings indicate that generated force is directly proportional to the wire diameter. Additionally, the total output force which represents the difference between generated force and the resistive force, shows minimal variation across different mandrel sizes. The response time is observed to be independent of the mandrel sizes and wire diameters.