**3. Results and Discussion**

The FEA model developed in the previous section was used to investigate the stress distributions resulting from different peening schemes in order to better understand how combinations of peening parameters influence residual stress distributions in thin sections. Only one-sided peening without a backing material was considered, reflecting the potential future application of in situ treatment of thin aircraft components. All simulations used a 5 mm × 5 mm square laser spot.

In general, a favorable state of residual stress for mitigating fatigue has several key characteristics. First, sufficient compression should exist at the surface and in the near-surface regions of critical areas of the component to offset fatigue-inducing tensile stresses. Second, the distribution and magnitude of the compensatory tension that arises from the LP process should not initiate a failure event when fatigue loads are applied. Third, for a line of peen spots that align with and overlay a surface scratch, such as the geometry considered in [10,12], near-surface tensile stresses transverse to the peen line should be absent to prevent premature initiation of a crack from the scratch.
