Effects of Laser Peening on Rotating Bending Fatigue Strength of Additive Manufactured Maraging Steel in Very High Cycle Fatigue Regime

Additive-manufacturing technology has attracted attention for the fabrication of components with complex shapes. However, the low fatigue strength of the metals produced via additive manufacturing poses a significant challenge. In this study, rotating–bending fatigue tests were performed on additive-manufactured maraging steel up to the very-high-cycle fatigue (VHCF) range (108 cycles). The effect of laser peening (LP) on the fatigue strength was examined. The LP introduced compressive residual stress near the surface, whereas tensile residual stress was generated internally. The fracture initiation point of the non-LP specimen was observed at the surface in the low-cycle range and in the interior in the VHCF range. In contrast, all the LP specimens fractured from the interior. LP was effective for increasing the fatigue strength in the low-cycle range; however, it reduced the fatigue strength in the VHCF range. The effect of LP on the VHCF strength was examined by focusing on the stress level at the fracture initiation point. Furthermore, the distribution of the defect size on the polished and fractured surfaces of the specimens was evaluated using extreme-value statistics. The results indicated that extreme-value statistics are effective for predicting the defect size in practical applications.