Mechanical Durability of Polymer-Encapsulated Electronic Yarns for Electronic Textile Applications

This study presents a standalone yarn-level assessment of the mechanical and functional durability of polymer-encapsulated electronic yarns (E-yarns) for wearable electronic textile applications. The investigated E-yarns consisted of miniaturised electronic components soldered onto fine conductive wires, protected by polymer encapsulation, and enclosed within braided textile yarn structures. This heterogeneous architecture enables textile-compatible functionality but creates local regions that may be susceptible to damage under various deformation modes. E-yarns incorporating light-emitting diode, photodiode, and resistor components were evaluated under cyclic bending fatigue, torsional fatigue, quasi-static tensile loading, and wash durability conditions. Electrical measurements were used to monitor functional degradation and failure, while X-ray imaging, scanning electron microscopy and finite element analysis were used to examine structural damage, failure localisation, fracture surface morphology, and local stress and strain distribution. The results show that E-yarn durability depended on the imposed loading condition, with distinct mechanical and functional responses observed across the different test modes. The polymer-encapsulated region emerged as a mechanically important feature of the E-yarn architecture, particularly at transitions between encapsulated and non-encapsulated regions. By addressing multiple deformation and loading conditions at the standalone yarn level, this work provides a systematic reliability assessment of polymer-encapsulated E-yarns, enabling intrinsic failure mechanisms to be distinguished from textile integration effects and supporting the development of more reliable yarn-based electronic textiles.