Ma J, Cawley P
UK Research Centre in NDE, Imperial College, London SW7 2AZ, United Kingdom.
J Acoust Soc Am. 2010 Jun;127(6):3485-93. doi: 10.1121/1.3409446.
Defect characterization using guided ultrasonic waves remains a challenging subject and requires a full understanding of the interaction of guided waves with a realistic representation of the defect. The characteristics of pulse echo reflection of the SH0 mode from part-thickness elliptical defects in plates is studied via finite element analysis and experimental measurements. The study shows that the reflection ratio spectrum of the SH0 mode from an elliptical defect exhibits periodic pattern due to interference between reflections from the two edges of the defect. The pattern of the reflection ratio spectrum is determined by the ratio of defect length in the incidence direction to wavelength, while the magnitude is affected by the maximum depth and the effective aspect ratio of the defect. Both the pattern and magnitude of the reflection ratio spectrum are found to be highly sensitive to the incidence angle, and the form of the variation of the reflection with angle is a strong function of the defect shape. In addition, a study of circular defects with tapered depth profiles reveals that the reflection is a function of average length of the tapered defect to wavelength ratio, and the magnitude of the reflection diminishes as the ratio increases.
使用导波进行缺陷表征仍然是一个具有挑战性的课题，需要充分理解导波与缺陷的实际表征之间的相互作用。通过有限元分析和实验测量，研究了板中部分厚度椭圆形缺陷的SH0模式脉冲回波反射特性。研究表明，由于缺陷两边反射之间的干涉，椭圆形缺陷的SH0模式反射率谱呈现出周期性模式。反射率谱的模式由缺陷在入射方向上的长度与波长之比决定，而幅度则受缺陷的最大深度和有效纵横比影响。发现反射率谱的模式和幅度对入射角都高度敏感，并且反射随角度变化的形式是缺陷形状的强函数。此外，对具有锥形深度轮廓的圆形缺陷的研究表明，反射是锥形缺陷平均长度与波长之比的函数，并且随着该比值增加，反射幅度减小。
