PSI - Issue 18

Fokion Oikonomidis et al. / Procedia Structural Integrity 18 (2019) 142–162 Dr Fokion Oikonomidis/ Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 19. Extensometer output during the 3 rd step load of 8109kN.

The acoustic emission sensors were used to detect the machine noise and environmental noise to define the threshold to trigger the AE-signal for the full test (Fig. 20). The criteria that were used for possible crack growth were the AE cumulative energy, and AE cumulative counts. During the application of step load 1 (5200kN) and step load 2 (7035kN), the AE technique did not detect any clear indication of crack growth. Fig. 21 shows the total cumulative energy for peak amplitude filters 45dB, 55dB and 65dB. It can be seen that the cumulative energy with a filter of 45dB starts to increase in an exponential way form the mid duration of step load 3 and continues during the application of step load 4. The other AE feature which showed a similar pattern was the cumulative counts. In Fig. 21, the slope increases sharply between 1450 and 1750hrs (mid-duration of step load 3). Then towards the end of step load 3 the cumulative counts increase at a slower rate. Finally, the slope of the curve increases again during the application of the 4 th step load.

Fig. 20. Noise recorded before the test: [Left] from the machine, [Right] from the environment.