PSI - Issue 13

Hikaru Yamaguchi et al. / Procedia Structural Integrity 13 (2018) 1183–1188 Hikaru Yamaguchi/ Structural Integrity Procedia 00 (2018) 000 – 000

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3. Experimental Results 3.1. Drop-weight tear test

Figure 4 shows high-speed camera images of specimen deformation in DWTT. From these images, crack-tip location and crack opening displacement at 2mm behind crack-tip were identified, from which crack velocity and CTOA were determined. Figure 5 shows crack velocity and CTOA. After reaching the maximum, 10 to 12m/s, crack velocity decreased steadily. CTOA was initially decreased and showed steady state, following unsteady change possibly due to the specimen end effect. The steady state was realized at crack length of about 15 to 32mm. At this state, CTOA resistance value was 22degrees in average. Crack velocity changed from c.a. 10m/s down to 4m/s. It should be noted that the crack was propagating in shear-mode and that the obtained CTOA resistance value was that at specimen surface. In any case, fairly constant CTOA resistance value was obtained in the DWTT. 0ms 2ms 4ms 6ms 0ms 2ms 4ms 6ms

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Fig.4 High-speed camera images of DWTT.

Fig.5 Crack velocity and CTOA measured by DWTT

3.2. Burst test Figure 6 shows test pipe before and after burst. Burst pressure was 16.5MPa. Crack propagated axially in the both direction and was arrested at about 1.5m from pipe center. Figure 7 shows change of crack velocity determined from stain gauge measurement, in which timing of crack-tip arrival was determined as the time of strain-peak at each location. The crack velocity decreased from c.a. 200m/s to 100m/s. Figure 8 shows a series of high-speed camera images on the north side. It is recognized that the crack propagated straightly in the axial direction and symmetrically with respect to the circumferential direction. Figure 9(a) shows higher magnification of one of the high-speed camera images. Points were plotted along the crack edge 10 mm behind the crack tip, linearly approximated and the angle made by the two straight lines was determined. However, this angle is a value on the observation surface, shown as a blue plane in Fig. 9(b). So, it was converted to that observed from the top of the pipe and the converted value was defined as CTOA resistance value. Because the image resolution was not high, the CTOA value obtained in this way might contain considerable error. Figure 10 shows change of the CTOA resistance value with crack length. The CTOA resistance value is seen to stay nearly constant, about 12 to 18degrees at 100 to 1500mm crack length where the crack was assumed to propagate steadily. This value was somewhat smaller than that measured by the DWTT.