PSI - Issue 64

Alamgir Khan et al. / Procedia Structural Integrity 64 (2024) 539–548 Alamgir khan / Structural Integrity Procedia 00 (2019) 000–000

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fluctuations in electrical resistivity. Fig 5 (c) indicates that CNCB2 has a better FCR response, reversibility, and strain sensitivity but a lower FCR response. After the heat treatment of CNCB2 at 400 °C, the load/stress sensitivity and FCR response gradually decreased with repeated cyclic compressions of 18%, 22%, and 26%, at 10-20 kN, in comparison with CNCB2 at 200 °C. The lower FCR response was due to the matrix and MWCNT/NCB damage after the exposure to 400 °C.

3E-2

(a) CNCB1

15 30 45 60 75 90

15 30 45 60 75 90

Load FCR

(b) CNCB1

Strain FCR

20

2E-2

10

1E-2

0E+0

0

-1E-2

Strain

FCR (%)

-45 -30 -15 0

-45 -30 -15 0

FCR (%)

-10 Load (kN)

-2E-2

-20

-3E-2

0 100 200 300 400 500 600 700 800 900 -30

0 100 200 300 400 500 600 700 800 900

Time (s)

Time (s)

30

30

3E-2

(d) CNCB2

(c) CNCB2

Strain FCR

Load FCR

20

2E-2

20

20

1E-2

10

10

10

0E+0

0

0

0

-1E-2

Strain

FCR (%)

FCR (%)

-10

-10

-10 Load (kN)

-2E-2

-20

-20

-20

-3E-2

-30

-30

0 100 200 300 400 500 600 700 800 900 -30

0 100 200 300 400 500 600 700 800 900

Time (s)

Time (s)

Fig.5 Piezoresistivity of the MWCNT/NCB copolymer fillers at elevated temperatures (400 °C).

3.5 Microstructural investigation of MWCNT/NCB composite fillers SEM images of the conductive networks of the CAC-based CNCB1 and CNCB2 are shown in Fig. 6. The MWCNT/NCB synergetic effect significantly enhances the mechanical properties, electrical conductivity, and piezoresistivity at normal and elevated temperatures. Furthermore, the SEM images reveal that the MWCNT/NCB composite fillers can be uniformly dispersed, resulting in a cooperative conductive network as the number of conductive paths increases with the addition of MWCNT/NCB. It is evident from the results that CNCB2 increases both the compressive strength and electrical conductivity compared to CNCB1 at normal and elevated temperatures. However, minor surface damage to the MWCNT and NCB was observed at an elevated temperature of 400 °C, which led to a decrease in the compressive strength, electrical conductivity, and piezoresistivity of CNCB1 and CNCB2. The thermal stability of the MWCNT in compression with NCB was significantly better at elevated temperatures.