Local Defect Resonance (LDR) is exploited for non-destructive testing (NDT) by using ultrasonic vibrations to get a localized resonant activation of defected zones. The LDR technique relies on the local stiffness difference between the defect and the sound material. Analyzing the structure's displacement field at this localized resonance frequency reveals the defect's location and provides information about the defect's characteristics, i.e. geometry, size and depth. In this study, the opportunities and limitations of linear LDR for NDT of materials are investigated in a parametric way. Both finite element simulations and experiments (using scanning laser Doppler vibrometry) are performed for aluminum alloy and carbon fiber reinforced polymer coupons with flat bottom holes and delaminations ranging in both depth and diameter. The resonance frequencies as well as the associated defect-to-background ratios are parametrically evaluated. For shallow defects, a clear LDR is observed caused by the strong local stiffness reduction at the defect. On the contrary, deep defects are associated with a limited stiffness decrease that results in the absence of LDR behavior. The local stiffness reduction at damages is further exploited using a weighted band power calculation. It is shown that using this technique, deep defects can be detected for which no LDR behavior was observed.

中文翻译：

---

探索用于深度缺陷检测的全场线性局部缺陷共振识别的极限

局部缺陷共振 (LDR) 通过使用超声波振动来获得缺陷区域的局部共振激活，用于无损检测 (NDT)。LDR 技术依赖于缺陷和声音材料之间的局部刚度差异。在此局部共振频率下分析结构的位移场可以揭示缺陷的位置并提供有关缺陷特征的信息，即几何形状、尺寸和深度。在这项研究中，以参数化的方式研究了线性 LDR 对材料无损检测的机会和局限性。对铝合金和碳纤维增强聚合物试样进行了有限元模拟和实验（使用扫描激光多普勒测振仪），这些试样具有平底孔和深度和直径范围内的分层。参数化评估共振频率以及相关的缺陷与背景比。对于浅缺陷，观察到明显的 LDR 是由缺陷处的强烈局部刚度降低引起的。相反，深度缺陷与有限的刚度降低相关，导致 LDR 行为的缺失。使用加权带功率计算进一步利用损坏时的局部刚度降低。结果表明，使用这种技术，可以检测到没有观察到 LDR 行为的深层缺陷。深部缺陷与有限的刚度降低相关，从而导致缺乏 LDR 行为。使用加权带功率计算进一步利用损坏时的局部刚度降低。结果表明，使用这种技术，可以检测到没有观察到 LDR 行为的深层缺陷。深部缺陷与有限的刚度降低相关，从而导致缺乏 LDR 行为。使用加权带功率计算进一步利用损坏时的局部刚度降低。结果表明，使用这种技术，可以检测到没有观察到 LDR 行为的深层缺陷。