Abstract: Shape memory alloys (SMAs) are smart materials with superelasticity originating from a reversible stress-induced martensitic transformation (MT) accompanied by a significant electrical resistance change. How-ever, the stress-strain and resistance-stress relationships of typical NiTi wires are non-linear due to the stress plateau during the stress-induced MT. This limits the usage of these materials as pressure sen-sors. Herein, we propose a high-strength flexible sensor based on superelastic NiTi wires that achieves near-linear mechanical and electrical responses through a low-cost double-braided strategy. This micro-architectured strategy reduces or even eliminates stress plateau and it is demonstrated that the phase transformation of microfilaments can be controlled: regions with localized stress undergo the MT first, which is successively followed by the rest of the microfilament. This structure-dependent MT charac-teristic exhibits slim-hysteresis superelasticity and tunable low stiffness, and the braided wire shows improved flexibility. The double-braided NiTi microfilaments exhibit stable electrical properties and re-peatability under approximately 600 MPa (8 % strain) and can maintain stability over a wide temperature range (303-403 K). Moreover, a cross-grid flexible woven sensor array textile based on microfilaments is further developed to detect pressure distribution. This work provides insight into the design and applica-tion of SMAs in the field of flexible and functional fiber.

Key words: NiTi, Shape memory alloys, Braiding, Near-linear responses, Flexible pressure sensors