Twisted Fibre Artificial Muscles

Artificial muscle technology has seen vast advancements since its inception in the 1950s. The impetus for artificial muscle research is to overcome many of the inherent short comings of traditional actuators such as their limited scalability and movement flexibility. In an effort to further advance the field of artificial muscles this thesis focused on the twisted composite fibre variety of artificial muscles, and aimed to improve on the current state-of-the-art through a better understanding of the fundamental mechanics that drive these actuators, and optimisation of materials, compositions and preparation technique. Niobium yarns containing a volume changing hydrogel guest material exhibited the ability to actuate torsionally under a certain stimulus, that is: exert a torque and generate a torsional stroke of up to 175°/mm. These torsional actuators were used to test a theoretical model for predicting torsional stroke with good correspondence between empirical and theoretical outcomes. The niobium yarns were, however, inconsistent in fabrication, which led to the desire to improve methods for fabricating twisted composite fibres. A range of material types were compared qualitatively and quantitatively using a screening method for preparation of optimised twisted fibre yarns. Notably, cotton and silk yarns performed well when used in composites with a specific hydrogel achieving ~60% unaided return up-twist post actuation. Due to its favourable performance and fibre morphology, cotton was chosen for further experiments. It was imbued with HydroMed hydrogel and showed torsional actuation through swelling-deswelling mechanisms comparable with actuators made from more exotic materials which were described in the literature.