Intelligent smart materials can not only monitor the damage and degradation of architectural structures in real time but also the health structure. In recent years, carbon nanotubes materials have emerged to possess both excellent mechanical and electrical properties. Moreover, when carbon nanotubes are added to epoxy resin, intelligent composite materials with significant sensitivity are created. In this study, the stress–strain curves and anelasticity of carbon nanotube/epoxy resin composites with different carbon nanotube concentrations is analyzed. Through changing the level of carbon nanotubes using the two-pole method, the percolation threshold of carbon nanotube/epoxy composites was determined. Thereafter, the effect of temperature on the composites’ conductive properties was investigated. Moreover, using the stepwise cyclic loading method, the piezoresistivity of the carbon nanotube/epoxy composites was investigated. The test results show that the elastic limit, the yield point, and the elastic modulus range of the carbon nanotube/epoxy composites is approximately 45 MPa, 50 MPa, and 1–2 GPa, respectively. The anelasticity of the carbon nanotube/epoxy composites increases with the gradual increase of the stress level. The percolation threshold interval of carbon nanotube/epoxy composites ranges from 0.5 to 1.0 wt%. The rate of change of resistance for the different concentrations on carbon nanotube/epoxy specimens corresponds to the temperature. Notably, the carbon nanotube/epoxy composites have better discrimination and pressure sensitivity for different grades of load. When the carbon nanotube content is 0.5 wt%, the sensitivity of the carbon nanotube/epoxy composites pressure-sensitive property is the largest, which is in agreement with the threshold curve. The results of this investigation have implications for the application of carbon nanotube/epoxy composites in structural health monitoring.

中文翻译：

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碳纳米管-环氧树脂复合材料的智能特性

智能智能材料不仅可以实时监测建筑结构的损坏和退化，还可以实时监测结构的健康状况。近年来，碳纳米管材料已经出现，具有优异的机械和电性能。此外，当将碳纳米管加入环氧树脂中时，会产生具有显着敏感性的智能复合材料。在这项研究中，分析了不同碳纳米管浓度的碳纳米管/环氧树脂复合材料的应力-应变曲线和非弹性。通过使用二极法改变碳纳米管的含量，确定了碳纳米管/环氧树脂复合材料的渗透阈值。此后，研究了温度对复合材料导电性能的影响。此外，使用逐步循环加载方法，研究了碳纳米管/环氧树脂复合材料的压阻率。测试结果表明，碳纳米管/环氧树脂复合材料的弹性极限、屈服点和弹性模量范围分别约为45 MPa、50 MPa和1-2 GPa。碳纳米管/环氧树脂复合材料的弹性随着应力水平的逐渐增加而增加。碳纳米管/环氧树脂复合材料的渗透阈值区间为 0.5 至 1.0 wt%。碳纳米管/环氧树脂样品上不同浓度的电阻变化率对应于温度。值得注意的是，碳纳米管/环氧树脂复合材料对不同等级的负载具有更好的辨别力和压力敏感性。当碳纳米管含量为 0.5 wt% 时，碳纳米管/环氧树脂复合材料压敏性能的灵敏度最大，与阈值曲线一致。这项调查的结果对碳纳米管/环氧树脂复合材料在结构健康监测中的应用具有重要意义。