The Effects of Process Variations on Residual Stress Induced by Laser Peening

Measurements of the distribution of residual stress with depth from the surface in laser peened coupons were made in a high-strength aluminum alloy. Residual stresses were measured using slitting (also known as the crack compliance method). Measurements were made on several coupons to: compare laser peening (LP) and shot peening residual stresses; ascertain the influence of LP parameters on residual stress; determine whether tensile residual stress existed outside the peened area; assess the variation of residual stress with in-plane position relative to the layout of the laser spots used for peening; and, determine the importance of a uniform spatial distribution of laser energy within the spot. Residual stress 0.1 mm from the surface due to LP and shot peening were comparable and the depth of the compressive stress for LP was far greater than for shot peening. Variations of most LP parameters did not significantly alter residual stress at shallow depths. Residual stresses adjacent to the peened area were found to be compressive. Decreased levels of surface residual stress were found when laser spots had a non-uniform distribution of laser intensity.