Fatigue life and performance evaluation of wearable flexible thermoelectric devices under thermomechanical loads

Abstract

Wearable flexible thermoelectric generators (WFTEGs) offer a promising solution for integrating power sources with electronics in wearable technologies. However, the longevity of these devices is compromised by fatigue propagation in brittle thermoelectric materials due to internal cracks. This study presents a three-dimensional (3D) numerical model of WFTEGs with through-thickness cracks, accounting for body heat and thermal contact resistance. The effects of flexible substrate thickness, heat sink convection coefficient, and bending radius on the output power density, conversion efficiency, and fatigue life of WFTEGs are comprehensively examined. The results reveal that although increased body heat enhances thermoelectric performance, it simultaneously reduces fatigue life. Removing the cold-end flexible substrate and utilizing an efficient heat sink can improve both thermoelectric performance and fatigue life. Interestingly, the fatigue life initially decreases but then increases as the bending radius decreases, which is attributed to the crack closure effect on fatigue crack propagation. To prevent accelerated fatigue and optimize device durability, environments with a bending radius of approximately 14.33 mm should be avoided. These findings provide valuable insights into the structural optimization of WFTEGs, ensuring their long-term reliability and safety.