Okudan Gorkem, Xu Chenxi, Danawe Hrishikesh, Tol Serife, Ozevin Didem
Department of Civil, Materials, and Environmental Engineering, University of Illinois at Chicago, United States.
Department of Mechanical Engineering, University of Michigan, United States.
Ultrasonics. 2022 Aug;124:106728. doi: 10.1016/j.ultras.2022.106728. Epub 2022 Mar 15.
The fundamental torsional wave mode, T(0,1), is typically preferred in monitoring defects in long-range pipe-like structures due to non-dispersive and low attenuation characteristics such that the wave packet is not distorted with distance. However, the sensitivity of T(0,1) wave mode depends on the defect type and orientation. While it is highly sensitive to cracks along the axis of pipes, the sensitivity to detect thickness change is low as T(0,1) wave mode generates tangential displacement motion around the pipe circumference. In this study, a gradient-index phononic crystal (GRIN-PC) lens is integrated into a steel pipe to manipulate its dispersion characteristics such that the phase velocity of T(0,1) wave mode is affected by the overall change in pipe thickness. The modified behavior of T(0,1) wave mode within the GRIN-PC lens region increases the damage detection capability of T(0,1) wave mode. Numerical models involving a parametric unit cell study indicate that the phase velocity of T(0,1) wave mode decreases as the thickness of the pipe with the GRIN-PC lens decreases, in contrast with the conventional pipe. The signal difference coefficient (SDC) is applied to the acquired signal from the focal point of GRIN-PC lens to quantify the uniform thickness change. Full-scale wave propagation simulations involving solid mechanics coupled with the piezoelectric actuation demonstrate that the SDC increases as the thickness decreases. The numerical results are validated with experiments using three steel pipes with different wall thicknesses.
由于具有非色散和低衰减特性，使得波包不会随距离而失真，基本扭转波模式T(0,1)通常更适合用于监测长距离管状结构中的缺陷。然而，T(0,1)波模式的灵敏度取决于缺陷类型和方向。虽然它对沿管道轴线的裂纹高度敏感，但由于T(0,1)波模式在管道圆周周围产生切向位移运动，其检测厚度变化的灵敏度较低。在本研究中，将梯度折射率声子晶体（GRIN-PC）透镜集成到钢管中，以操纵其色散特性，使得T(0,1)波模式的相速度受到管道厚度整体变化的影响。GRIN-PC透镜区域内T(0,1)波模式的改变行为提高了T(0,1)波模式的损伤检测能力。涉及参数化晶胞研究的数值模型表明，与传统管道相比，随着带有GRIN-PC透镜的管道厚度减小，T(0,1)波模式的相速度降低。将信号差异系数（SDC）应用于从GRIN-PC透镜焦点获取的信号，以量化均匀厚度变化。涉及固体力学与压电驱动耦合的全尺寸波传播模拟表明，随着厚度减小，SDC增大。使用三根不同壁厚的钢管进行实验验证了数值结果。
