Fig. 1. Schematic diagram of traditional laser shock peening

Fig. 2. Schematic diagram of DSLS

Fig. 3. Schematic diagram of DNLSP

Fig. 4. The variation of residual stress on workpiece surface with impact mode (one side: SLSP; zero phase: DSLSP)^[26]

Fig. 5. The topography of the workpiece and the absorption film^[29]. (a) The surface morphology of the workpiece; (b) 3D morphology of the workpiece; (c) Surface morphology of the absorption layer; (d) 3D morphology of the absorption layer

Fig. 6. Double-sided laser shock peening stress wave propagating in the blade^[30]. (a) DSLSP; (b) DNLSP

Fig. 7. Residual stress induced by DSLSP^[11]. (a) Surface residual stress; (b) Residual stress in the thickness direction

Fig. 8. Residual stress field of DLSP. (a) Effect of sheet thickness on the residual stress field of DSLSP^[27]; (b) Residual stress field of DNLSP^[34]

Fig. 9. Stress distribution at the edge induced by double-sided laser shock peening^[30]. (a) DNLSP; (b) DSLSP

Fig. 10. Titanium alloy sheet subject to DNLSP^[22]. (a) Transverse plastic strain distribution in the thickness direction; (b) Equivalent bending moment of SLSP and DLSP under different energy; (c) Parts after laser shock peening; (d) Contour graph

Fig. 11. Crack propagation path^[38]. (a) Before grain refinement; (b) After grain refinement

Fig. 12. Unfavorable stress distribution induced by DSLSP^[41]

Fig. 13. Two different scan paths^[43]. (a) Z-scan path; (b) Optimized scanning path

Fig. 14. Different laser shock processing strategies^[46]. (a) Path 1; (b) Path 2; (c) Path 3

Fig. 15. Different laser shock processing strategy^[35]. (a) Strategy 1; (b) Strategy 2; (c) Strategy 3

Fig. 16. Influence of region design of DSLSP on the strengthening effect^[47]. (a) Impact zone design; (b) Life extension effect; (c) Edge collapse

Fig. 17. Different DSLSP loading modes in two impact regions^[48]. (a) Geometric dimensions of the workpiece; (b) Impact area 1; (c) Impact area 2

Fig. 18. Soft and hard alternate energy absorption structures and grain distribution refined by laser shock peening. (a) Soft and hard alternating energy absorbing structures; (b) Grain distribution refinement^[48]

Fig. 19. Schematic illustrations of laser shock wave interaction on Mg-Al-Mn alloy sheet subjected to DSLSP^[49]. (a) One-sided LSP impacts; (b) Two-sided and simultaneous LSP impacts for the thin sheet; (c) Two-sided and simultaneous LSP impacts for the thin sheet

Fig. 20. Variation of residual stress along the thickness direction^[52]