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

1156

5

electrodes with 5 to 10 times higher values. The samples are collected from the same batch of MCF which can be considered a similar sectional area, hence, it can be observed the similar tendency for the corresponding electrical resistivity. The distance between the outer electrodes is twice of the inner electrodes, indicating that the electrical resistivity of MCF with outer electrodes is almost 10 times lower than that of MCF with inner electrodes. For the former, the electrodes have direct contact with the cross-sectional area of the fiber bundle, allowing electrons to transmit directly within the fiber bundle. This is different from the latter, which only makes contact with the surface of the outer filaments.

2.4×10 −3

15

2.2×10 −4

3.0

(a)

(b)

13.2

2.3

2.0×10 −4

11.9

2.5

2.2×10 −3

12

10.5

Electrical resistance ( Ω )

1.8 Electrical resistance ( Ω ) 0.5 1.0 1.5 2.0

Electrical resistivity ( W ·m)

9.8

Electrical resistivity ( W ·m) 3 6 9

1.8×10 −4

2.0×10 −3

1.4

1.6×10 −4

1.3

1.8×10 −3

1.4×10 −4

1.2×10 −4

1.6×10 −3

1.0×10 −4

1.4×10 −3

0

0.0

SI1

SO1

SI2

SO2

SI3

SO3

SI4

SO4

Groups

Groups

Fig. 3. Electrical resistance and resistivity of MCF with different electrode configurations: (a) MCF with outer electrodes; (b) MCF with inner electrodes.

3.2. Stress-sensing characteristics Fig. 4 illustrates the stress-sensing performances of four MCF samples with two outer electrodes subjected to cyclic flexural stress, namely SO1, SO2, SO3, and SO4, respectively. It can be observed that the variations of fractional changes of resistance (FCR) among different samples are relatively significant, which can be explained by the differences in the microstructure of the individual samples. For SO1, there is a sudden increase of FCR at the beginning of loading which is likely owing to the unstable microstructures of MCF and the detachment of carbon fibre. Nevertheless, from the last two cycles of loading, it can be observed that the resistance values continue to decrease with the applied load, indicating a negative piezoresistivity with FCR changes in the range of 1.0%. In terms of SO2 and SO3, The FCR variation is relatively smooth, showing excellent stability without fluctuations, especially in the immediately manifested negative piezoresistivity after loading. However, compared to the SO1, the FCR values are much smaller within the range of 0.3%. Although sensitivity has decreased, the stability appears to have improved. Interestingly, the stress-sensing performance of SO4 is entirely different from the previous samples. The FCR increases with loading and decreases with unloading, exhibiting positive piezoresistive behavior. The potential reason is the carbon fibre movement of delamination within the MCF, which induces gaps and disconnects the neighboring carbon yarns. However, this needs further research and a wider range of data.