Fig. 1. Lamb wave dispersion curves of 0.2 mm thick silicon steel plate

Fig. 2. Schematic of method for measuring internal stress of strip steel based on laser ultrasonic guided waves

Fig. 3. Schematic of laser ultrasonic stress detection system

Fig. 4. Tensile specimen of silicon steel plate

Fig. 5. Flow chart of data analysis

Fig. 6. Time-domain waveform and normalized spectrum of laser ultrasonic guided wave. (a) Time domain waveform；(b) normalized spectrum

Fig. 7. Time domain waveform and envelope after band-pass filtering

Fig. 8. Laser ultrasonic guided wave signals under different stress states. (a) Head wave; (b) wave packet

Fig. 9. Influence of tensile stress on laser ultrasonic guided waves. (a) Head wave advance; (b) wave packet delay

Fig. 10. Relationship between relative change rate of guided wave group velocity and tensile stress

Fig. 11. Influences of tensile stress on laser ultrasonic guided waves in steel plates with different thicknesses. (a) Head wave advance; (b) wave packet delay