**2. Materials and Methods**

### *2.1. Characteristics of the Baseline Material*

The specimens used for the analysis were made of aluminum alloy 6082-T6, with the geometry given in Figure 2. The specimens were machined out of a 400 × 260 × 20 mm<sup>3</sup> plate, with a circular notch milled at the center. A Mitutoyo Surface Roughness Tester (Mitutoyo Italiana, Lainate, Italy) was used to measure the surface roughness at the notch—five measurements were taken on each specimen and the nominal roughness was found to be equal to 3.2 μm. The thickness of the specimen was high enough, so that it did not warp during the peening process. The geometry of the specimen was similar to that reported in the literature [15] for three-point bending fatigue tests, with the central notch acting as a stress concentration for the easier localization of the fatigue crack nuclei.

**Figure 2.** Specimen geometry. The midline path (*s*) and the local coordinates are shown in the detailed view of the notch.
