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Small Defect Detection Through Local Analysis of Acoustic Spatial Wavenumber

机译:通过声空间波数局部分析检测小缺陷

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We present some preliminary results in utilizing laser-acquired steady-state ultrasonic response measurements for detecting small defects such as out-of-plane cracking. In our approach, we exploit the local discontinuity in the material impedance, which leads to sharp spatial gradients in the steady-state wave field and manifests as high local wavenumber content in the spatial Fourier domain. We demonstrate the ability to detect, localize, size, and orientate cracks using two techniques: curvature estimation and high-frequency wavenumber imaging. For curvature estimation, we make robust estimates of the Laplacian at each point in two-dimensional steady-state response. In the wavenumber imaging, we high-pass filter the response measurement just above the nominal guided wave wavenumber, and calculated the two-dimensional envelope using the monogenic signal. Both techniques proved effective on two aluminum plate samples, one with 100% through-thickness cracking at a fastener, and one with a 50% through thickness notch on the rear face.
机译:我们提出了一些利用激光获得的稳态超声响应测量来检测小缺陷(例如面外裂纹)的初步结果。在我们的方法中,我们利用了材料阻抗中的局部不连续性,这导致稳态波场中出现尖锐的空间梯度,并在空间傅立叶域中表现为较高的局部波数含量。我们展示了使用两种技术检测,定位,确定大小和定向裂缝的能力:曲率估计和高频波数成像。对于曲率估计,我们对二维稳态响应中每个点的拉普拉斯算子进行了稳健的估计。在波数成像中,我们对正好在标称导波波数之上的响应测量值进行高通滤波,并使用单基因信号计算二维包络。两种技术都被证明对两个铝板样品有效,其中一个在紧固件处有100%的穿透厚度开裂,而另一个在背面有50%的穿透厚度开槽。

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