In Twisting Motion, Stress‐Free Zone of Wearable Electronics

Abstract

Flexible electronics, such as flexible displays, batteries, and sensors, are under active development, and their mechanical reliability under repeated mechanical deformations is receiving a lot of attention. The mechanical stress under simple bending has been widely investigated, and the neutral plane located tensile and compressive region has been suggested for stress‐free zone under bending. However, to develop highly reliable twistable electronics, it is essential to elucidate the stress evolution during complex twisting deformation, and determine the stress‐free zone in twisting. The mechanical reliability of flexible indium tin oxide and Cu patterns during repeated twisting motions is reported. For fixed twisting, the patterns at the center show higher stability, but for free twisting, the patterns at the edge exhibit superior mechanical reliability. The mechanical stress evolution in twisting motion is analyzed by finite element method simulation, and the stress‐free zone according to twisting motion and base is proposed. Finally, the stress‐free zone is verified by conducting real twisting tests, such as the twisting motion of the human body. This study based on experimental reliability testing and computational simulation can provide guidelines to develop highly reliable twisting electronics.

Finite element analysis of stress distribution in soft sensors under torsional loading

“…During practical applications these sensors operate under intermittent or cyclic mechanical deformations such as bending, stretching, twisting and a combination of these. The sensor response changes with induced stresses during these mechanical movements, and often device failure occurs after repeated stress cycles [17][18][19]. Therefore, greater attention is needed to predict the response of flexible systems under various mechanical deformations [19][20][21].…”

“…Whilst few attempts have been made in this regard, most of the previous studies have focused only on the analysis of mechanical stress distribution and its effect on device performance under tensile and compressive bending and stretching conditions [13,19,[22][23][24][25][26]. Whilst these encouraging works mark a step in the right direction, a very few of them have aimed to understand the stress evolution under twisting (torsional) loading [17,18,27].…”