Experimental characterization of thermally-activated artificial muscles based on coiled nylon fishing lines

The discovery of an innovative class of thermally activated actuators based on twisted polymeric fibres has opened new horizons toward the development of effective devices that can be easily manufactured using inexpensive materials such as fishing lines or sewing threads. These new devices show large deformations when heated together with promising performance in terms of energy and power densities. With the aim of providing information and data useful for the future engineering applications, we present the results of a thermo-mechanical characterization conducted on a specific type of twisted polymeric fibre (i.e. nylon-made coiled actuators) that is considered particularly promising. A custom experimental test-bench and procedure have been developed and employed to run isothermal and isometric tensile tests on a set of specimens that are fabricated with a simple and repeatable process. The results of the experiments highlight some important issues related to the response of these actuators such as hysteresis, repeatability, predictability and stored elastic energy.