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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the load/strain sensitivity. The heat-exposer smart sensors demonstrated that the FCR was highly dependent on the temperature and enhanced the piezoresistivity of CNCB1-CNCB2; however, irreversibility in the FCR for lower concentrations of CNCB1 was observed after 200 °C. Further increase in cyclic compression loading amplitudes improved the reversibility of CNCB1 and exhibited an increase in the FCR response of 43 %, 45 %, and 46% at 10 20 kN after heat treatment at 200 °C, as shown in Fig. 4 (a). Fig. 4 (c) shows the FCR response of CNCB2 at 200 °C with 29%, 33%, and 35% enhancement at 10-20 kN respectively. The FCR response of CNCB2 was greatly enhanced after heat treatment in comparison with CNCB2 at a normal temperature.

(b) CNCB1

(a) CNCB1

Strain FCR

10 20 30 40 50

Load FCR

10 20 30 40 50

2E-2

20

1E-2

10

0E+0

-60 -50 -40 -30 -20 -10 0

-60 -50 -40 -30 -20 -10 0

0

-1E-2

Strain

FCR (%)

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)

10 20 30 40

(c) CNCB2

(d) CNCB2

2E-2

Strain FCR

Load FCR

10 20 30

20

1E-2

10

0E+0

-40 -30 -20 -10 0

-40 -30 -20 -10 0

0

-1E-2

Strain

FCR (%)

-10

FCR (%)

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

Time (s)

Time (s)

Fig.4 Piezoresistivity of the MWCNT/NCB composite fillers at elevated temperatures (200 °C).

3.4 Piezoresistivity investigation at 400 ˚ C temperature To further evaluate and understand the effects of elevated temperature and fire resistance behavior response at 400 °C, Fig. 5 (a-d) show the load/strain sensitivity, reversibility, and piezoresistivity of CNCB1-CNCB2 after heat treatment. Fig 5 (a) shows the CNCB1 FCR response and strain sensitivity at a 10-20 kN load. Very sharp changes in the FCR response were observed at low, medium, and high cyclic loading. The FCR (+) response values exhibited a sharp and irreversible response caused by microcracks at the surface, where conductive network breakages and minor cracks were further observed with gradually increasing cyclic compression loading, resulting in large