*3.1. Fatigue Tests*

A total of eight specimens were tested—four samples (denoted as 2, 3, 4, and 5) were LPwC-treated, as described above; the other four (6B, 7B, 8B, and 9B) were untreated and served as a baseline for comparison. The Maximum Stress–Number of cycles (S–N) results of the two cases are plotted in Figure 9. Two distinct S–N curves are fitted through the data of the peened and unpeened samples using the least-squares method. Even if four specimens are not sufficient for constructing a statistically significant S–N curve, the trends obtained from fatigue testing are very clear. The fatigue life of the treated specimens was found to be longer for all load levels, with a maximum increase equal to 3.34 times the baseline value.

**Figure 9.** S–N curves from the fatigue tests. The maximum nominal stresses vs fatigue lives of the tested specimens are plotted. Least-square fittings of the untreated and peened samples are shown in red and blue, respectively.
