PSI - Issue 42

Nikola Schmidová et al. / Procedia Structural Integrity 42 (2022) 1306–1313 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1310

5

Table 1. The measured electrical resistance differs among the specimens, the highest measured value is more than 80% greater than the lowest value. For better comparison among measured data, an increase of measured electrical resistance for each specimen Δ R is given in the graphs. The increase of electrical resistance Δ R was calculated as

Table 1 Measured electrical resistance during flexural loading

El. resistance after fracture (loaded) RAF ( Ω )

El. resistance of pristine specimen

El. resistance before fracture RBF ( Ω )

Peak el. resistance during fracture

After fracture relative resistance change (RAF-RBF)/R0 (%)

Specimen Number

Peak relative resistance change (RP-RBF)/R0 (%)

Signal fluctuation

R0 ( Ω )

RP ( Ω )

(%)

8 9

0.135 0.117 0.193 0.107

0.125 0.129 0.206 0.101

0.132 0.154

0.130 0.120 0.176 0.109

5.2

3.8

0 0 0

21.5

-7.7

10 11

no peak

no peak

-15.8

0.015

-80.6

7.9

2.4

Fig. 5 Evaluation of the after fracture relative resistance change.

initial electrical resistance before loading R0 (given in Table 1) subtracted from actual measured electrical resistance. Relative bending moment Mo rel was calculated according the following formula: = ∙ 100[%] , where (1) = ∑ . (2) Results for three cycles of operational loading are given in Fig. 3. A dependence between applied load and measured electrical resistance change can be see for specimens SN-9 and SN-11. For specimen SN-8 we can observe slightly decrease in measured electrical resistance change when the applied load is rising. On the other hand, opposite trend can be seen in electrical resistance change measured for specimen SN-10. We can observe big increase of measured electrical resistance during first increase of bending moment and another slight increase for next two loading cycles. Based on the highest measured electrical resistance of pristine specimen together with the different measured dependency for the specimen SN-10, we can assume, that is caused by slightly damaged electrical contacts. We can observed also slightly different curve of measured electrical resistance change during static loading for specimen SN-10 compared to other specimens, see Fig. 4. For specimens SN-8, SN-9 and SN-11 we can observe slightly decrease of measured electrical resistance change, which could be caused by the minor damage in the structure, which could cause increase in electrical conductivity of the specimen. For specimen SN-10 we observe