Characterization of laser peening residual stresses in Al 7075 by synchrotron diffraction and the contour method

Laser peening is a mechanical surface treatment, used to improve the fatigue performance of metallic materials. The gains in performance derive from a deep case of compressive residual stress generated in the near-surface region. This compressive residual stress field is balanced by residual tension. The residual stress state has been characterized in two Al 7075 plate samples, one laser peened only at its centre and the other overlap peened over most of the top surface. The residual stress depth profiles were measured using energy dispersive synchrotron X-ray radiation. The profiles revealed greater compression in the sample peened at a single position. The samples were subsequently characterized using the contour method. The technique allowed the residual stress to be determined in 2D to the very near surface. Depth profiles of the two techniques exhibited good agreement.