Shape-memory actuation in aligned zirconia nanofibers for artificial muscle applications at elevated temperatures

Abstract

Artificial muscle is one of the key technologies to accelerate the development of robotics, automation, and artificial-intelligence-embedded systems. This work aims to develop shape-memory ceramic (SMC) nanofiber-based coiled yarns for artificial muscle applications at elevated temperatures. Highly aligned SMC nanofiber (zirconia-based) yarns and springs have been successfully fabricated by electrospinning. The microstructure and tensile properties of the SMC nanofibers and the shape-memory actuation performance of the SMC yarns/springs have been characterized. A significant shape-memory effect with a recoverable strain of up to ∼5% and short recovery time (0.16 s) has been demonstrated in the SMC yarns at actuation temperatures of 328-388 °C. The SMC springs can lift up to 87 times their own weight when heated by a Bunsen burner, and the stroke is 3.9 mm. The SMC yarns/springs exhibit an output stress of 14.5-22.6 MPa, a work density of 15-20 kJ//m3, and a tensile strength of 100-200 MPa, which are much higher than those of human muscles and some other polymer-based artificial muscles. Benefiting from the advantages of large output stress, high tensile strength, high actuation temperatures, and fast response, the SMC nanofiber-based yarns/springs have a great potential to be used as artificial muscles at elevated temperatures.