Fig. 1. Sectional dimension of rail

Fig. 2. Model of rail surface under laser irradiation

Fig. 3. Gaussian space and time equivalents of point source and line source. (a) Space equivalent of line source;(b) space equivalent of point source; (c) time equivalent

Fig. 4. Convergence analysis of grids. (a) Grid size of 0.3 mm; (b) grid size of 0.05 mm

Fig. 5. Waveforms in time domain under different grid sizes. (a) 0.3 mm; (b) 0.2 mm; (c) 0.1 mm;(d) 0.075 mm; (e) 0.05 mm

Fig. 6. Ultrasonic speed cloud maps. (a) Point source at 9 μs; (b) point source at 29 μs; (c) line source at 9 μs;(d) line source at 29 μs

Fig. 7. Ultrasonic waveforms in time domain excited by point source and line source. (a) Point source; (b) line source

Fig. 8. Laser ultrasonic detection system

Fig. 9. 60 kg rail sample. (a) Real object; (b) schematic of defects

Fig. 10. Experimental results of ultrasonic waves excited by point source and line source. (a) Point source; (b) line source

Fig. 11. Models of two defects. (a) Model of defect 1;(b) model of defect 3

Fig. 12. Ultrasonic speed cloudmaps for models of two defects. (a) Defect 1, at 3 μs; (b) defect 3, at 9 μs; (c) defect 1, at 18 μs; (d) defect 3, at 29 μs

Fig. 13. Ultrasonic signals in time domain for models of two defects. (a) Simulation signal for defect 1;(b) simulation signal for defect 3; (c) experimental signal for defect 1; (d) experimental signal for defect 3