Study on detection of angled surface cracks with laser-generated Rayleigh waves

Detection of an angled surface crack in a sample with laser-generated Rayleigh waves is studied.Based on the thermoelastic coupled equations in the frequency domain,the finite element method is adopted to establish the model of the angled crack detections by using the laser-generated Rayleigh waves.The detecting mechanisms of the angled cracks are investigated.The transient displacement waveforms are calculated numerically in the samples with the angled cracks of different lengths and orientation angles.The interactive process of mode-conversion of the Rayleigh waves on the angled cracks is analyzed,and the propagation paths of the various Rayleigh waves are studied.In addition,the influences of the crack width and the material viscoelasticity on the Rayleigh wave propagations and crack detections are also obtained.The results show that the crack positions and lengths can be detected by the arrival times of the reflected and transmitted Rayleigh waves that are generated by the interaction of the crack and Rayleigh wave.Moreover, the crack orientation angles are also determined using a shear wave that is generated through mode conversion of the Rayleigh wave at the bottom crack tip.The numerical results agree well with the existing experimental measurements. It indicates that the effective theoretical basis can be obtained for angled surface cracks detections.