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On the piezoresistive behavior of carbon fibers - Cantilever-based testing method and Maxwell-Garnett effective medium theory modeling

Yao, Yanbo, Luo, Jiangjiang, Duan, Xiaoshuang, Liu, Tao, Zhang, Yonggang, Liu, Baihua, Yu, Muhuo
Carbon 2019 v.141 pp. 283-290
carbon, carbon fibers, engineering, models
A good understanding of the piezoresistive behavior of carbon fiber is highly valuable in studying the processing-structure-property relationship of this very important engineering material. Up-to-date, there is still a lack of agreement on the physical origin of the unique modulus-dependent piezoresistivity for carbon fibers. In the present work, an experimental and theoretical modeling combined approach was taken to attack this long outstanding issue. A cantilever testing method was developed which allows for the evaluation of the piezoresistive behavior of a single carbon fiber filament under axial tension and compression mode. It was found that the tensile and compressive piezoresistive behavior showed antisymmetric characteristics. This supports the concept that the orientation of the basic structural units (BSUs) is responsible for the piezoresistivity of carbon fibers. Such an argument was further augmented by theoretical modeling of the carbon fiber piezoresistivity based on a Maxwell Garnett theory approach. The new piezoresistivity model identifies the critical role of the compound effect of the BSU orientation and its volume fraction in dictating the piezoresistive behavior of carbon fibers. With consideration of this compound effect, the modulus-dependent piezoresistivity data of carbon fibers reported in the past few decades can now be well explained.