Okudan Gorkem, Danawe Hrishikesh, Zhang Lu, Ozevin Didem, Tol Serife
Department of Civil, Materials, and Environmental Engineering, University of Illinois at Chicago, Chicago, IL 60607, USA.
Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109, USA.
Materials (Basel). 2021 Mar 22;14(6):1552. doi: 10.3390/ma14061552.
Phononic crystals have the ability to manipulate the propagation of elastic waves in solids by generating unique dispersion characteristics. They can modify the conventional behavior of wave spreading in isotropic materials, known as attenuation, which negatively influences the ability of acoustic emission method to detect active defects in long-range, pipe-like structures. In this study, pipe geometry is reconfigured by adding gradient-index (GRIN) phononic crystal lens to improve the propagation distance of waves released by active defects such as crack growth and leak. The sensing element is designed to form a ring around the pipe circumference to capture the plane wave with the improved amplitude. The GRIN lens is designed by a special gradient-index profile with varying height stubs adhesively bonded to the pipe surface. The performance of GRIN lens for improving the amplitude of localized sources is demonstrated with finite element numerical model using multiphysics software. Experiments are conducted using pencil lead break simulating crack growth, as well as an orifice with pressured pipe simulating leak. The amplitude of the burst-type signal approximately doubles on average, validating the numerical findings. Hence, the axial distance between sensors can be increased proportionally in the passive sensing of defects in pipe-like geometries.
声子晶体能够通过产生独特的色散特性来控制固体中弹性波的传播。它们可以改变各向同性材料中波传播的传统行为，即衰减，而衰减会对声发射方法在长距离管状结构中检测有源缺陷的能力产生负面影响。在本研究中，通过添加梯度折射率（GRIN）声子晶体透镜来重新配置管道几何形状，以提高由诸如裂纹扩展和泄漏等有源缺陷释放的波的传播距离。传感元件设计成围绕管道圆周形成一个环，以捕获具有改善幅度的平面波。GRIN透镜是通过一种特殊的梯度折射率分布设计的，其中高度不同的短柱通过粘合剂粘结到管道表面。使用多物理场软件的有限元数值模型展示了GRIN透镜在提高局部源幅度方面的性能。实验使用模拟裂纹扩展的铅笔芯折断以及模拟泄漏的带压力管道的孔口进行。突发型信号的幅度平均大约翻倍，验证了数值研究结果。因此，在管状几何形状的缺陷被动传感中，传感器之间的轴向距离可以成比例增加。
