Institute of Structural Lightweight Design, Johannes Kepler University Linz, Altenberger Str. 69, 4040 Linz, Austria.
Sensors (Basel). 2022 Aug 25;22(17):6403. doi: 10.3390/s22176403.
The present paper comprehensively investigates the complex interaction between ultrasonic guided waves and local structural discontinuities, such as damages, through highly sensitive features: so-called wave damage interaction coefficients (WDICs). These WDICs are unique for each structural discontinuity and depend solely on their characteristics for a given structure and condition. Thus, they can be particularly useful for advanced assessment of lightweight structures in the context of non-destructive evaluation and structural health monitoring. However, the practical application of WDICs entails significant difficulties due to their sensitivity and complex patterns. Therefore, this study attempts to guide researchers and practitioners in the estimation of WDICs from numerical simulations and physical experiments. Detailed investigations are made for an aluminum host plate modified by artificial structural discontinuities, i.e., surface-bonded steel sheets. The numerical simulations are performed to predict WDICs and study sensitivities using a sophisticated finite element model. The experimental setup uses piezoelectric transducers to excite guided waves in the host plate. A single scanning laser Doppler vibrometer measures the scattered guided waves caused by the surface-bonded steel sheets, and the resulting WDICs with possible influences are investigated. In both cases, the orientation and thickness of the attached steel sheets were varied to create 12 different damage scenarios. In general, the comparison between numerical and experimental WDICs show good agreement. This underpins the applicability of the general methodology for simulating and measuring WDICs over all scenarios. Furthermore, the WDIC scattering patterns reveal a clear dependency of the peaks in the back-scattered reflections for both the numerical and experimental amplitude coefficients on the damage orientation, basically following the law of reflection. However, some discrepancies between both studies were observed. Numerical sensitivity analysis identified the adhesive layer as one reason for such differences. Additionally, misalignment errors in the experimental measurements were also found to affect WDICs. Therefore, an improved baseline subtraction method is proposed, which clearly enhances the experimental WDICs. Finally, an experimental sensitivity study of WDICs for selected sensing radii revealed only a minor influence. All these investigations were made for the amplitude as well as the phase representation of WDICs. Thus, these findings may open the way to future research and development of techniques employing WDICs for advanced applications of non-destructive evaluation and structural health monitoring.
本文全面研究了超声导波与局部结构不连续性（如损伤）之间的复杂相互作用，通过高度敏感的特征：所谓的波损伤相互作用系数（WDICs）。这些 WDICs 对于每个结构不连续性都是独特的，并且仅取决于它们在给定结构和条件下的特征。因此，它们对于轻量级结构的无损评估和结构健康监测的高级评估可能特别有用。然而，由于 WDICs 的敏感性和复杂模式，实际应用它们会带来重大困难。因此，本研究试图指导研究人员和从业者从数值模拟和物理实验中估计 WDICs。详细研究了通过人工结构不连续性（即表面粘结钢板）修改的铝合金母材。使用复杂的有限元模型进行数值模拟以预测 WDICs 并研究敏感性。实验设置使用压电换能器在母材中激励导波。单个扫描激光多普勒测振仪测量由表面粘结钢板引起的散射导波，并研究可能影响的结果 WDICs。在这两种情况下，都改变了附加钢板的方向和厚度，以创建 12 种不同的损伤场景。通常，数值和实验 WDICs 之间的比较显示出良好的一致性。这支持了针对所有场景模拟和测量 WDICs 的通用方法的适用性。此外，WDIC 散射模式显示出数值和实验振幅系数的背散射反射峰的峰值对损伤方向有明显的依赖性，基本上遵循反射定律。然而，在这两项研究中观察到一些差异。数值敏感性分析将粘合层确定为产生这种差异的原因之一。此外，还发现实验测量中的对准误差也会影响 WDICs。因此，提出了一种改进的基线扣除方法，该方法明显增强了实验 WDICs。最后，对选定感应半径的 WDICs 的实验灵敏度研究表明影响很小。所有这些研究都是针对 WDICs 的幅度和相位表示进行的。因此，这些发现可能为未来的研究和开发技术开辟道路，这些技术将 WDICs 用于无损评估和结构健康监测的高级应用。
