PSI - Issue 19

R.B. Kalombo et al. / Procedia Structural Integrity 19 (2019) 688–697 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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load cell which is in series with the cable. The vibration of the sample on the bench is made by using an electrodynamic shaker which is connected to the cable with the alignment device. To detect the strand break of the cable during the test, a device is mounted on the cable at a point with a low vibration, which is the first node from the LPC (Kalombo et al. 2015). The recommendations of CIGRÉ and the Institute of Electrical and Electronics Engineers (IEEE) on the fatigue test of cable were used during the experimental campaign. Therefore, the bending displacement ( Y b ) was controlled and kept constant. All fatigue tests were performed according to IEEE and CIGRÉ standards where the established criterion to stop the cable´s fatigue test is when the number of broken strands amounts to 10% of the total number of cable aluminium strands (Cham 2006, Kalombo et al. 2015). The bending strain of the cable was measured using three strain gauges glued onto the three top strands diametrically opposite to the LPC, as recommended by IEEE and CIGRÉ. The amount of cycles to failure was counted by pointing a laser on the cable and the bending displacement was measured and controlled during the fatigue test (Fig. 3).

Three strain gauges glues on the cable at the diametrically opposite point of LPC

Cable

Accelerometer at 89 mm from LPC

Laser at 89 mm for counting the number of cycles

Fig. 3. The system cable/suspension clamp on the resonance fatigue test bench with different sensors.

Three different bending stress values were used and the test was repeated three times for each bending stress to generate the S-N graph for each cable with a H/w value of 1820 m. Thus, eighteen fatigue tests were performed, with nine fatigue tests for each cable to generate the S-N graph. The parameters used to conduct the fatigue test are presented in Table 3.

Table 3. Parameters used during the fatigue test; the banding amplitude ( Y b ) at 89 mm, the Poffenberger-Swart constant ( K ) and the bending stress calculated using Eq. 2 and 1, respectively.

H/w (m)

Cable type

EDS (%UTS)

Poffenberger-Swart constant, K (MPa/mm)

Bending stress, (MPa) 26.8 28.22 31.35 Bending displacement, Y b (mm)

AAC Orchid

1820 31.4

30.91

0.87

0.91

1.01

AAAC 823 MCM

1820 21.6

32.66

0.82

0.86

0.96