Flexible sensing materials have attracted tremendous attention in recent years because of their potential applications in the fields of health monitoring, artificial intelligence, and so on. However, the preparation of rate sensing materials with self-healing performance is always a huge challenge. Herein, we first report the design and synthesis of a highly stretchable, recyclable, self-healing polysiloxane elastomer with rate sensing capability. The elastomer is composed of a dynamic dual network with boron/oxygen dative bonds and hydrogen bonds, which overcomes the structural instability of conventional solid–liquid materials. It exhibits certain adhesion, satisfactory mechanical robustness, and superior elongation at break (up to 1171%). After heating treatment at 80 °C for 2–4 h, the mechanical properties of damaged materials can be almost completely restored. Because of the “solid–liquid” property of the elastomer, it has irreplaceable functions which can sense different rates by resistance change after blending with multiwalled carbon nanotubes, principally in the range of 10 mm/min–150 mm/min. Especially, this rate sensing elastomer can be personalized by 3D printing at room temperature. This rate sensing strategy coupled with the introduction of dynamic dual-network structure is expected to help design advanced wearable devices for human rhythmic movement.

In this paper, a series of graphitic carbon nitride (g-C 3 N 4 ) was synthesized under different thermal oxidation etching temperatures and epoxy/g-C 3 N 4 composites were prepared via solution blending. The morphology and structure of g-C 3 N 4 were investigated by transmission electron microscope, X-ray diffraction (XRD), Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The tensile fracture morphology and structure of epoxy resin (EP) composites were demonstrated by scanning electron microscopy and XRD, respectively. Mechanical properties of EP composites were characterized by tensile testing, and the thermal performances were investigated by dynamic mechanical thermal analysis and thermal gravimetric analysis. The results revealed that the active groups on g-C 3 N 4 sheets increased under thermal oxidation etching and the C to N ratio of g-C 3 N 4 decreased from 0.94 to 0.76 with the increasing etching temperature. Noticeably, the tensile strength of EP composites was enhanced by 58% with the addition of C 3 N 4 -NS-500 and the thermal properties were also improved significantly, including T 0.5 (the decomposition temperature at the mass loss of 50%) increased by 21.5 C and glass transition temperature improved by 8 C. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48598.

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The oil film among meshing teeth is just like a spring-damping element, and it can dominate the friction and meshing characteristics of the gear pair and influence its dynamic performances further. Thus, this article focuses on a double-helical gear system and makes efforts to consider the effect of the oil film among meshing teeth more deeply, which can enhance the precision of dynamic analysis for the gear system. First, based on the elasto-hydrodynamic lubrication theory and “microtomy” method, the models of friction and meshing characteristics are developed including the friction state and spring-damping effect of the oil film among meshing teeth; then, the dynamic models of the double-helical gear system with the effect of the oil film among meshing teeth are established, and finally, the experiments are carried out to verify the value of the models developed in this article. According to the theoretical and experimental analyses, it can be seen that the dynamic model considering the effect of the oil film among the meshing teeth is more precise and practical, and the effect of the oil film should be considered in the dynamic analysis of the gear system, especially at the condition with heavy load or high speed.

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