PSI - Issue 19

Lloyd Hackel et al. / Procedia Structural Integrity 19 (2019) 346–361 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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For the next test another welded panel was configured with one third of the exposure area partially laser peened and the remaining area left un-peened. This ensured that both peened and un-peened areas were identically exposed to the same solution concentration, exposure time and temperatures. Figure 14 shows the test panel used. The weld and heat-affected zone ran through the middle of the exposed area. After 57.5 hours of exposure to the MgCl2 at 155°C the heaters were turned off, the solution solidified and the cell was removed allowing inspection of the panel surface. An array of photos was taken and stitched together with the resultant shown on the left side in Figure 15. The same photo with the cracks highlighted is shown on the right. Cracks had extensively developed in the heat affected zone with some cracking in the weld area. No cracks developed in the laser peened region and cracks that propagated into the laser peened region arrested. Figure 16 shows on the left a magnified view of a number of cracks propagating toward and arresting as they reach the laser peened region of the test panel. On the right the same view is shown with highlighting of the cracks. There were several noted areas in the laser peened region that were identified as pre-existing scratches that were confirmed upon inspection not to be cracks; this is further testament to the laser peening as scratches would nominally be considered stress-rising sites prone to crack initiation. Figure 18 shows a further magnified view of cracks in the unpeened region and shows cracks in the un-peened area that extensively developed around a scratch. This is in contrast to the peened area where cracks did not develop about a pre-scratched area.

Figure 14. Welded test panel with laser peened and un- peened exposed area. Panel is roughly 6” x 5” (152 x 127 mm) with strongbacks made of 316L stainless steel. Weld is approximately 0. 75” (19 mm) wide.