PSI - Issue 64

Wenkui Dong et al. / Procedia Structural Integrity 64 (2024) 1152–1159 Wenkui Dong and Macro liebscher et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 5. Stress-sensing performance of MCF with two inner electrodes subjected to cyclic flexural stress: (a) SI1; (b) SI2; (c) SI3; (d) SI4.

3.3. Mechanism discussion To explain the more reliable measurement set-up for MCF with inner electrodes under flexural stress, Fig. 6 schematically illustrates the movement of electrons in the carbon fibres under an external field with two different electrode configurations. For MCF with outer electrodes, due to the contact area mainly being on the cross-section of the carbon fibers, electron movement primarily occurs within the carbon fibers (orange portion), with a smaller portion moving through the surface of the carbon fibers (blue portion). This can be explained by the lower contact resistance with outer electrodes. In this scenario, despite the deformation of carbon fibers inducing contact between adjacent fibers under bending stress, since the majority of electron movement occurs at the cross-section, their direct contact does not lead to significant changes in their contact resistance and thereby the electrical resistance of MCF. On the contrary, for MCF with outer electrodes the movement of electrons more concentrated on the surface of the individual CFs. Therefore, changes in surface conditions, such as contact between fibers during bending, will more noticeably bring about alterations in contact resistance and overall resistance. This also explains why the FCR exhibits more fluctuation and irregularity for the MCF with inner electrodes, as the contact conditions between carbon fibers are more complex.