Production and performance of a low temperature shape-memory actuator based on twisted-coiled spring mechanics

Abstract

Demand for new types of actuators continues to grow, and novel approaches have been made possible by the advent of new materials and fabrication strategies. Self-powered actuators have attracted significant attention owing to their ability to be driven by elements in ambient environments. This type of actuator can be used in flexible strain sensors, artificial muscles, soft robotics, and smart breathing textiles. However, petrochemical-based polymers are generally environmentally unfriendly and cause ecological problems. The use of biodegradable polymers is one of the preferred solutions to ecological problems. Polylactic acid is a biodegradable and biocompatible polymer with a high potential. In this study, nanoclay reinforced polylactic acid/thermoplastic polyurethane was used as a precursor. The yarn that was produced was highly twisted. The twisted yarn was then shaped into a coiled structure via mandrel annealing. An apparatus was designed to investigate the thermal actuation behavior of twisted-coiled yarn in an isometric state. The blocked force and free stroke were calculated in an isometric state by using linear material equations. The thermal actuation behavior of the twisted-coiled yarn was also studied in the isotonic state. This precursor exhibited a considerable two-way shape-memory effect in a twisted-coiled structure. It also showed a significant reversible contraction stroke within the low temperature range. The theoretical stroke was determined using two different models: the force–stroke equation and spring mechanics. The theoretical results were compared with the experimental results, which revealed acceptable agreement between the theoretical and experimental values.