School of Civil and Environmental Engineering, Georgia Institute of Technology, 30332 Atlanta, GA, United States.
Department of Civil and Environmental Engineering, Northwestern University, 60208 Evanston, IL, United States.
Ultrasonics. 2014 Aug;54(6):1470-5. doi: 10.1016/j.ultras.2014.04.020. Epub 2014 May 2.
This research presents a new technique for nonlinear Rayleigh surface wave measurements that uses a non-contact, air-coupled ultrasonic transducer; this receiver is less dependent on surface conditions than laser-based detection, and is much more accurate and efficient than detection with a contact wedge transducer. A viable experimental setup is presented that enables the robust, non-contact measurement of nonlinear Rayleigh surface waves over a range of propagation distances. The relative nonlinearity parameter is obtained as the slope of the normalized second harmonic amplitudes plotted versus propagation distance. This experimental setup is then used to assess the relative nonlinearity parameters of two aluminum alloy specimens (Al 2024-T351 and Al 7075-T651). These results demonstrate the effectiveness of the proposed technique - the average standard deviation of the normalized second harmonic amplitudes, measured at locations along the propagation path, is below 2%. Experimental validation is provided by a comparison of the ratio of the measured nonlinearity parameters of these specimens with ratios from the absolute nonlinearity parameters for the same materials measured by capacitive detection of nonlinear longitudinal waves.
本研究提出了一种新的非线性瑞利表面波测量技术，该技术使用非接触式空气耦合超声换能器；与基于激光的检测相比，这种接收器对表面条件的依赖性较小，而与接触式楔形换能器的检测相比，其准确性和效率更高。提出了一种可行的实验装置，能够在一定的传播距离范围内对非线性瑞利表面波进行稳健、非接触式的测量。相对非线性参数是通过绘制归一化二次谐波幅度与传播距离的关系得到的斜率来获得的。然后，使用该实验装置评估了两种铝合金试样（Al 2024-T351 和 Al 7075-T651）的相对非线性参数。结果表明，所提出的技术是有效的 - 沿传播路径的位置测量的归一化二次谐波幅度的平均标准偏差低于 2%。实验验证是通过将这些试样的测量非线性参数的比值与通过电容检测非线性纵向波测量的相同材料的绝对非线性参数的比值进行比较来提供的。
