Defect reconstruction is essential in non-destructive testing and structural health monitoring with guided ultrasonic waves. This paper presents an algorithm for reconstructing notches in steel plates which can be seen as artificial defects representing cracks by comparing measured results with those from a simulation model. The model contains a parameterized notch, and its geometrical parameters are to be reconstructed. While the algorithm is formulated and presented in a generalized form for many different defect types, a special case of guided wave propagation is used to investigate one of the simplest possible simulation models that discretizes only the cross-section of the steel plate. An efficient simulation model of the plate cross-section is obtained by the semi-analytical Scaled Boundary Finite Element Method. The reconstruction algorithm applied is gradient-based, and Algorithmic Differentiation calculates the gradient. The dedicated experimental setup excites nearly plane wave fronts propagating orthogonal to the notch. A scanning Laser Doppler Vibrometer records the velocity field at certain points on the plate surface as input to the reconstruction algorithm. Using two plates with notches of different depths, it is demonstrated that accurate geometry reconstruction is possible.

翻译：缺陷重构对于基于导波的无损检测与结构健康监测至关重要。本文提出一种通过对比实测数据与仿真模型结果，重构钢板中（可视为代表性人工缺陷）凹槽的算法。该模型包含参数化凹槽，旨在重构其几何参数。虽然算法以通用形式针对多种缺陷类型进行描述，但本文采用导波传播的特例，研究了仅离散钢板横截面的最简仿真模型之一。通过半解析缩放边界有限元法获得高效的板横截面仿真模型。所应用的重构算法基于梯度优化，并通过算法微分计算梯度。专用实验装置激发近似平面波前，使其沿垂直于凹槽方向传播。利用扫描激光多普勒测振仪记录板表面特定点的速度场，作为重构算法的输入。通过两块具有不同深度凹槽的钢板验证了精确几何重构的可行性。