Fatigue Testing of Wearable Sensing Technologies: Issues and Opportunities

Abstract

Standards for the fatigue testing of wearable sensing technologies are lacking. The majority of published fatigue tests for wearable sensors are performed on proof-of-concept stretch sensors fabricated from a variety of materials. Due to their flexibility and stretchability, polymers are often used in the fabrication of wearable sensors. Other materials, including textiles, carbon nanotubes, graphene, and conductive metals or inks, may be used in conjunction with polymers to fabricate wearable sensors. Depending on the combination of the materials used, the fatigue behaviors of wearable sensors can vary. Additionally, fatigue testing methodologies for the sensors also vary, with most tests focusing only on the low-cycle fatigue (LCF) regime, and few sensors are cycled until failure or runout are achieved. Fatigue life predictions of wearable sensors are also lacking. These issues make direct comparisons of wearable sensors difficult. To facilitate direct comparisons of wearable sensors and to move proof-of-concept sensors from “bench to bedside,” fatigue testing standards should be established. Further, both high-cycle fatigue (HCF) and failure data are needed to determine the appropriateness in the use, modification, development, and validation of fatigue life prediction models and to further the understanding of how cracks initiate and propagate in wearable sensing technologies.

Interconnecting embroidered hybrid conductive yarns by ultrasonic plastic welding for e-textiles

“…In our study, a break in the electrical connection or an increase in resistance by 150% is defined as a contact fault. 45…”

“…In our study, a break in the electrical connection or an increase in resistance by 150% is defined as a contact fault. 45 After carrying out the welding tests according to the full factorial test plan, all samples were examined by means of four-point electrical resistance measurement. It turned out that the results can be divided into two groups.…”

Electromechanical Properties of 3D-Printed Stretchable Carbon Fiber Composites

“…Because clothing-integrated stretchable and wearable components endure thousands of stretching cycles during their lifetime [ 30 ], cyclic tensile loading was chosen as a more realistic testing method. The cyclic electromechanical behavior of the samples was tested with the simultaneous use of the tensile tester and a custom-built resistance measurement system (Tampere University, Tampere, Finland).…”

Comparison of the Capacitance of a Cyclically Fatigued Stretch Sensor to a Non-Fatigued Stretch Sensor When Performing Static and Dynamic Foot-Ankle Motions

“…Due to the limitations of MOCAP, methods to collect movement data, such as joint angles, in a non-clinical setting are desirable. To overcome the limitations of measuring joint angles in a non-clinical setting, video or photographic-based goniometer smartphone applications have been developed and validated to measure joint angles [ 2 , 3 ], personalized medical approaches using additive manufacturing (3D printing) techniques to print sensors using existing or novel materials that can be tailored to suit the needs of a particular patient are being explored [ 4 , 5 , 6 , 7 ], and research is ongoing in the development of a smart sock that utilizes capacitive stretch sensors to measure ankle joint angles in real-time during athletic events [ 8 , 9 , 10 , 11 , 12 , 13 , 14 ].…”

“…For example, to move the sock prototype from the laboratory to the basketball court, the sensors must be able to withstand low-cycle fatigue (LCF). Basketball players are estimated to take 1260 running steps per game [ 24 ]; however, 32 basketball games may be played in one regular season by a National Collegiate Athletics Association (NCAA) Division I (D1) basketball team exclusive of the conference and national tournaments, subjecting a sensor to approximately 40,320 cycles in a regular season moving the sensors into the high-cycle fatigue (HCF) regime [ 14 ]. Most fatigue studies of stretch sensors only capture LCF, and the durability of the materials and signal beyond a few thousand cycles remains uncertain [ 14 ].…”