PSI - Issue 42

J.R. Antunes et al. / Procedia Structural Integrity 42 (2022) 588–593

589

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Author name / Structural Integrity Procedia 00 (2019) 000–000

Figure 1. Fatigue dogbone samples design and dimensions.

2. Laser peening treatment Thorough optimisation of the laser parameters was undertaken to try to achieve compressive residual stresses of high magnitude (close to yield), while minimizing distortion. The best results were achieved using the parameters summarised in Table 1 and the layout illustrated in Figure 2, which were used to peen the FSW dogbone samples.

Table 1. Laser peening parameters.

Power density (GW/cm 2 )

Energy (J)

Spot size (mm)

α (°)

Nr layers 4 per side

Offset (%)

Overlap (%)

Tape

0.7

0.5

2

25

50

50

Steel (0.025mm)

Figure 2. Laser peening treatment layout.

The treatment was performed on both sides of the samples using 4 layers on each side and steel tape of 0.025 mm thickness was used as an ablative for optimal surface texture. This resulted in minimal distortion compared to the untreated samples. 3. Residual stress measurements The Incremental Central Hole Drilling Method (ICHDM) was used to measure the residual stress fields before and after the laser peening processing, using a system supplied by Stresscraft Ltd and rosette strain gauges of type VPG CEA-06-062UL-120. For each measurement, a 2 mm (nominal) hole is drilled into the samples by orbital hole milling and the changes in strain are recorded at depth increments of increasing size to a 1 mm total hole depth. For the as-welded samples before peening, one single measurement was done in the centreline of the shoulder side of the weld, as illustrated in Figure 3-a. For the peened samples, 3 measurements were done across the weld, as can be observed in Figure 3-b. Measurement A is on the centreline, B on the interface of the weld, and C is outside of the peening region. Additionally, in order to get the full mapping across the 2 mm depth, the samples were turned over and drilled again by maintaining a distance of at least 5 mm from the opposite previously drilled hole. These strain changes were interpreted using the Stresscraft RS INT software.