Abstract:

Objective Artificial muscles have shown great importance in the development of wearable devices, exoskeletons, prosthetics and robotics in recent years. Although many artificial muscles based on the novel actuation technologies have been reported, challenges such as single actuation form, complex processing and limited flexibility remain to be addressed. Textile-based artificial muscles exhibit high flexible and light weight properties, but the actuation performance still needs to be enhanced. In order to investigate and develop textile-based artificial muscles with high-performance, it is highly desirable to combine the active materials with textiles.
Method A thermally driven composite yarn actuator with Ni-Ti alloy as the core and polyimide (PI) fiber as the sheath was designed. Specifically, the Ni-Ti alloy filaments were covered by the PI fiber on a friction machine. Due to the good thermal stability of the PI fibers and excellent thermal actuate performance of Ni-Ti alloy filaments, the fabricated yarns can respond to the heat. In addition, thanks to the good conductivity of the alloy filaments the fabricated yarn and fabric are able to be actuated by the electrothermal.
Results A shape-programmable woven fabric actuator was successfully prepared using the composite yarn, the mechanical properties and thermally driven characteristics of the composite yarn and its fabric were initially explored. The results showed that the composite yarns exhibit a hierarchical structure with PI fiber uniformly covering the shape memory alloy filament, which greatly enhanced the wearability of the fabrics. The phase transition temperature of the shape memory alloy was determined by differential scanning calorimetry (DSC) analysis. The mechanical performance test results showed that as the temperature increases, the shape memory alloy filament transformed from the martensitic phase to the austenitic phase, leading to an increase in the modulus of the filament. The obtained yarns showed excellent electrical and thermal properties with temperature up to 35 ℃ under 2.5 V. In addition, the composite yarn can remain a stable temperature, which demonstrates the potential to be applied at low voltage and ability of regulating the temperature by various applied voltages and currents. The results of electrical and thermal driving tests showed that the yarn exhibits good electrical heating and thermal stability, and the higher the loaded current and voltage, the higher the yarn temperature and the shorter the time to reach the steady state. The thermal induced actuation test results show that the composite yarn and its fabric will recover to the initial linear state after being thermally driven. The yarn can be actuated within 6.2 s under 5 V and the angle returned to 135° in 3.4 s, indicating the fast actuation characteristic of the composite yarn. In addition, the high temperature resistant and shape programmable composite fabric actuator prepared by woven interval weft method enables different shape actuation. Due to the programmable properties of memory alloys, fabrics that have been annealed at high temperatures are able to exhibit different actuation movements.
Conclusion In this work, a shape memory alloy-based composite yarn was designed. The yarn was fabricated by covering the PI fiber on the shape memory alloy filament via a friction spinning machine. A shape programmable fabric actuator was fabricated by weaving technique. The mechanical properties and thermal actuation characteristics of the composite yarn and fabric were systematically investigated. Through the test results, the following conclusions are obtained: ① The higher the temperature, the higher the reversion stress of the shape memory composite yarn. ② The shape memory composite yarn has good electrical heating and thermal stability performance. ③ The prepared composite yarn has good electric heating performance. The actuating action can be completed within 6.2 s at 5 V. ④ The composite fabric actuator with high temperature resistance and shape programmable was prepared by weaving method. The fabric was shape-programmed to achieve different actuation motions. The shape-memory composite yarn and fabric can be applied in the fields of smart wearable devices and medical rehabilitation.

Key words: shape memory alloy filament, composite corespun yarn, soft actuator, programmable artificial muscle