A flexible carbon fibre-based electrothermal film for fast actuation of shape memory alloy sheets

Two-dimensional shape memory alloy (SMA) structures have great potential in intelligent and highly flexible robots. However, they have challenges in direct electric heating. This paper proposes a solution to heat SMA sheets using carbon fibres as surface heat sources and indirectly transmits Joule heat generated by the carbon fibres to the SMA sheets. The preparation process of the carbon fibre-based thermoelectric composite film is illustrated in this study. The effect of heat source (carbon fibre) distribution on heat transfer characteristics and the temperature field of the SMA surface is simulated. Then, a functional prototype integrated thermoelectric film and flexible SMA is fabricated, and its effectiveness is verified by local and global activation, respectively. The results show that the composite structure can recover deformation rapidly in 2 s with only 0.7 A running current (applied to each carbon fibre). In addition, the local temperature control method can also realize distributed (spatial dimension) and sequential (temporal dimension) control of the structure. The proposed solution is expected to expand further the design and control of complex, intelligent structures with the development of 4D printing technology.