Carandente R, Ma J, Cawley P
UK Research Centre in Non-Destructive Evaluation, Imperial College, London SW7 2AZ, United Kingdom.
J Acoust Soc Am. 2010 Jun;127(6):3440-8. doi: 10.1121/1.3373406.
Guided ultrasonic waves have been successfully applied to detect defects and corrosion in plates and pipes; however, defect sizing remains challenging due to the complex profiles of the defects encountered in practice. A study of the reflection of the fundamental torsional mode T(0,1) from an axi-symmetric defect with varying depth profile has been carried out via finite element modeling and experimental validation. Defects with gradually varying depth are represented by a series of tapered steps. It is revealed that, for both tapered up- and down-steps, the wave packet is reflected only at the start and end of the steps. The reflections from the start and end of the step have been predicted, and the frequency dependence of the overall reflection from the step has been studied. The study shows that the reflection coefficient varies as a function of the ratio of the average length of the tapered defect to the wavelength due to the interference between the waves reflected from the two ends of the defect. The reflection coefficient maxima decrease as the slope of the taper becomes more gradual, this effect being more pronounced when the ratio of the average defect length to the wavelength increases.
导波已成功应用于检测板材和管道中的缺陷及腐蚀情况；然而，由于实际中遇到的缺陷轮廓复杂，缺陷尺寸测量仍然具有挑战性。通过有限元建模和实验验证，对基本扭转模式T(0,1)从具有不同深度轮廓的轴对称缺陷处的反射进行了研究。深度逐渐变化的缺陷由一系列锥形台阶表示。结果表明，对于向上和向下的锥形台阶，波包仅在台阶的起始和末端反射。预测了台阶起始和末端的反射，并研究了台阶整体反射的频率依赖性。研究表明，由于从缺陷两端反射的波之间的干涉，反射系数随锥形缺陷平均长度与波长之比的函数而变化。随着锥形斜率变得更平缓，反射系数最大值减小，当平均缺陷长度与波长之比增加时，这种效应更为明显。
