Fig. 1. Schematic of numerical model

Fig. 2. Schematic of mesh generation

Fig. 3. Schematic of surface defect detection by SLS

Fig. 4. Displacement signals at upper surface by laser source irradiation for different distances from detection point. (a) 1 mm; (b) 1.2 mm; (c) 1.4 mm; (d) 1.7 mm; (e) 2.4 mm

Fig. 5. Displacement signals of laser-induced surface acoustic waves under different temperatures. (a) No defects; (b) with defects

Fig. 6. Waveforms in frequency domain of laser-induced surface acoustic waves under different temperatures

Fig. 7. Displacement waveforms at different defect depths

Fig. 8. Time difference δtAB versus defect depth under different temperatures

Fig. 9. Displacement waveforms at different defect widths

Fig. 10. Time difference δtAB versus defect width under different temperatures

Fig. 11. Finite element model of interaction between surface acoustic wave and front edge of defects

Fig. 12. Displacement fields of front edge of defects interacting with surface acoustic wave. (a) t=0.3 μs; (b) t=0.5 μs; (c) t=0.6 μs

Fig. 13. Propagation path produced by front edge of defects interacting with surface acoustic wave

Fig. 14. Signal in time domain of front edge of defects interacting with surface acoustic wave

Fig. 15. Finite element model of interaction between surface acoustic wave and rear edge of defects

Fig. 16. Displacement signal of surface acoustic wave interacting with rear edge of defects

Fig. 17. Displacement fields of rear edge of defects interacting with surface acoustic wave. (a) t=0.3 μs; (b) t=0.4 μs; (c) t=0.6 μs; (d) t=0.7 μs

Fig. 18. Schematic of propagation of feature point K

Fig. 19. Schematic of interaction process between surface acoustic wave and surface defects