Ultrasonically Patterning Silver Nanowire-Acrylate Composite for Highly Sensitive and Transparent Strain Sensors Based on Parallel Cracks

It has long been a challenge to develop strain sensors with large gauge factor (GF) and high transparency for a broad strain range, to which field silver nanowires (AgNWs) have recently been applied. A dense nanowire (NW) network benefits achieving large stretchability, while a sparse NW network favors realizing high transparency and sensitive response to small strains. Herein, a patterned AgNW-acrylate composite-based strain sensor is developed to circumvent the above trade-off issue via a novel ultrasonication-based patterning technique, where a water-soluble, UV-curable acrylate composite was blended with AgNWs as both a tackifier and a photoresist for finely patterning dense AgNWs to achieve high transparency, while maintaining good stretchability. Moreover, the UV-cured AgNW-acrylate patterns are brittle and capable of forming parallel cracks which effectively evade the Poisson effect and thus increase the GF by more than 200-fold compared to that of the bulk AgNW film-based strain sensor. As a result, the AgNW-based strain sensor possesses a GF of ∼10,486 at a large strain (8%), a high transparency of 90.3%, and a maximum stretchability of 20% strain. The precise monitoring of human radial pulse and throat movements proves the great potential of this sensor as a measurement module for wearable healthcare systems.

Determination of the Enhancement or Shielding Interaction between Two Parallel Cracks under Fatigue Loading

In this paper, the interactions between two parallel cracks are investigated experimentally and numerically. Finite element models have been established to obtain the stress intensity factors and stress distributions of the parallel cracks with different positions and sizes. Fatigue crack growth tests of 304 stainless steel specimens with the single crack and two parallel cracks have been conducted to confirm the numerical results. The numerical analysis results indicate that the interactions between the two parallel cracks have an enhancement or shielding effect on the stress intensity factors, depending on the relative positions of the cracks. The criterion diagram to determine the enhancement or shielding effect between two parallel cracks is obtained. The changes of the stress fields around the cracks have been studied to explain the mechanism of crack interactions.