PSI - Issue 60

S.S. Satpute et al. / Procedia Structural Integrity 60 (2024) 525–534

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S. S. Satpute et. al./ Structural Integrity Procedia 00 (2023) 000–000

due to monotonically increasing loading. The calculation of the crack growth is shown in Fig. 6 with schematic drawing among grid points. The straight crack growth between point 00 and 01 is opening of already existing hairline crack, which is shown as solid red line. The crack growth is shown in dotted line beyond grid point 12, which starts at certain deviated angle after blunting of crack tip. This vertical projected length of dotted line should be considered as crack growth ∆ due to applied loading. Fig 7 (a) and Fig. 7 (b) depict the images Load and LLD through camera focused on the monitor of the Servo Controller PC, and pictorial values of CMOD related multimetere values. Both crack tips images acquired online via both the related cameras are shown in Fig. 7(c) and Fig. 7(d). Thus, the predicted crack growth will be related to instantaneous applied Load, LLD, CMOD, etc. For a typical 12-inch pipe tested load vs. LLD data is shown in Fig. 8. Fig. 8(a) shows the crack growth vs. load where the crack growth is taken from the visible crack tip. However, it should be noted that this crack growth also includes the opening of the hairline crack already present due to fatigue pre cracking. Corrected average crack growth vs. load is shown in Fig. 8(b).

(a) Crack Growth of Both Crack Tips

(b) Crack growth after deducting fatigue pre-cracking

Fig. 8. Calculation of crack growth for a 12-inch welded pipe tested under monotonic loading

4.2. Cyclic Tearing Testing The image processing technique have also been implemented for through wall cracked pipe specimen under four- point cyclic loading. The variation of load is shown in Fig. 9 (a) where load is increasing up to peak load which is kept slightly lower than the load bearing capacity of the pipe specimen. Now this load is fully reversed in negative direction. It should be noted that both crack tips open during the positive and close for the negative . Thus, for acquiring the crack growth value under cyclic loading, the crack tip images are captured at positive and these images are post processed for crack growth prediction. For a typical 8-inch pipe with through wall cracked pipe tested under cyclic loading the crack growth and load variations vs. No. of load cycles are shown in Fig. 9 (b). similarly, the image processing technique has been employed for the prediction of crack growth for total five pipes as shown in Fig. 10. LC2 denotes an 8-inch CS SA333Gr6 pipe with surface crack while LC1, LC3, LC4 are the 8-inch CS SA333Gr6 pipes with through wall crack 60 degree, tested under different magnitude of cyclic loading, ��� . One 12-inch Stainless Steel Weld (SSW) pipe LC5 with through wall crack of 60 degree have also been tested under cyclic loading.