Fig. 1 Schematic diagram of shot peening test setup

Fig. 2 Residual stress measurement by using orbital hole-drilling method. a Target gauges installed on specimens, b setup for drilling (gauge 2)

Fig. 3 a Distribution of residual stress along the variation of depths for different shot peening pressures. b Influence of the various polishing times on the distribution of the residual stress of specimen

Fig. 4 Surface roughness variation under various treatment conditions in the different tests

Fig. 5 Fatigue life variation under various treatment conditions in the different tests

Fig. 6 SEM images of surface morphologies for the specimens under various shot peening pressures in the first batch of tests for: a SP30, b SP50, c SP70

Fig. 7 Fractographic images of specimens in the first batch of tests for: a intrinsic, b SP30, c SP50, d SP70. The red dotted line denotes the border of different layers, while the yellow dotted circle denotes the void located zone

Fig. 8 Fractographic images of specimens under shot peening and post-peening polishing treatments in the first batch of tests for: a SPV30, b SPV50, c SPV70. The red dotted line denotes the border of different layers, while the yellow dotted circle denotes the void located zone

Fig. 9 Surface morphologies of specimens in the second batch of tests for: a intrinsic, b VS, c VSP30, d VSP50, e VSP60, f VSP70

Fig. 10 Surface morphologies of specimens in the third batch of tests for: a intrinsic, b VSP, c VSP2H, d VSP4H, e VSP6H, f VSP8H