激光激发瑞利波检测表面倾斜缺陷的研究

研究激光激发瑞利波检测样品的表面倾斜缺陷。基于频域热弹耦合方程,采用有限元方法建立激光激发瑞利波检测倾斜缺陷的数值模型,研究倾斜缺陷的检测机理。数值计算含不同的长度及倾斜角度缺陷的样品中瞬态位移波形,分析瑞利波在倾斜缺陷处模式转换的过程,研究各种瑞利波的传播路径。在此基础上,研究缺陷宽度与材料黏性对瑞利波传播及缺陷检测的影响。结果表明:瑞利波在缺陷处产生的反射及透射瑞利波的到达观测点的时间可以检测缺陷位置和长度,瑞利波在缺陷的底部发生模式转换产生的切变波可以检测缺陷倾斜角度。数值结果和已有的实验结果一致,从而为表面倾斜缺陷的检测提供有效的理论依据。 

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.