Investigations for lowering pulse energy of laser-peening for improving fatigue strength

Laser peening can introduce compressive residual stress on the surface of various materials and, therefore, is effective in enhancing the fatigue strength. This study clarifies whether the laser peening with lower pulse energy comparing to the preceding studies generates compressive residual stress, and whether such stress would account for prolonged fatigue life in the welded zone of high-strength steel HT780. As a result, laser peening condition, which can generate large compressive residual stress on the base metal surface, were selected under the pulse energy of 6, 10 and 20 mJ, respectively. With the reduction of the pulse energy, it was observed that the depth of the compressive residual stress tended to decrease. Fatigue lives of the toe of the butt welded joints pretreated by laser peening with the selected conditions were prolonged to the same level of fatigue lives with the pulse energy of 200 mJ. © 2018 Japan Welding Society. All rights reserved.