Electromechanical Properties and Resistance Signal Fatigue of Piezoresistive Fiber-Based Strain Gauges

Piezoresistive nanocomposite fibers are essential elements for smart wearables and have recently become a research hotspot because of their high sensitivities at large deformations in the plastic regime. However, little attention has been paid to the electromechanical properties of such fibers at low strains where the resistance–strain (R–ε) relationship is reliably linear. In addition, prediction of the resistance signal stability for these materials during cyclic loading remains unreported. Here, we studied these two aspects using wet-spun piezoresistive nanocomposite fibers from polyether block amide (PEBA) composed of a hybrid conductive filler network of carbon black (CB) and carbon nanotubes (CNTs) in which the CB loading in the PEBA matrix was varied at a constant volume fraction of CNTs. We found the R–ε linear relationship (working factor, W) to increase with CB filler loading from 0.01 to 0.058. In addition, the gauge factors of these fibers varied inversely with W from 16.89 to 3.81. Using fatigue theory, we predicted the endurance limit of PEBA/CB-CNT fibers in the elastic regime to be ∼34.9 cycles. Although our fibers were extremely deformable, up to 500% strain, as is the case for most piezoresistive nanocomposite fibers, this work reveals the working range to be actually very small, comparable to rigid conventional strain gauges. We believe with PEBA/CB-CNT fibers' robust mechanical properties and the ease with which the electromechanical signal can be quantified with the fatigue model, they would be ideal materials to be integrated into textiles to perform as tough, finely tuned strain sensors for a range of rigorous bodily monitoring such as low-strain impacts and joint movements.