Development of a nonlinear acoustic microscope and evaluation of bond integrity

本项目的目的是利用非线性超声波无损检测结构材料和粘结界面中的微小微裂纹和/或脱落。其主要思想是检测在几十纳米的大振幅的突发超声波作用下微裂纹处产生的高次谐波。当微小微裂纹和/或剥离表面被反复拍打或摩擦时，高次谐波被激发，其频率是入射波频率的整数倍。本项目包括：(a) 2^<和>谐波的测量技术，不需要在被测材料表面粘贴压电元件；(b)消除耦合水的非线性，用于浸没测量；(c)采用动态有限元法对2^<和>谐波进行数值模拟，其中引入接触单元模拟近接触裂纹或界面。现将本项目的主要成果总结如下：1) .在大振幅突发波、商用压电换能器和数字信号处理方面，建立了一个2^<和>谐波测量系统。该系统检测到经入射波幅值归一化的A_2/A_1, 2^<和>谐波幅值比大于0.4%，分辨率为0.1%。2)在浸没测量中，开发了一种排除耦合水声非线性的传输技术。这对于扫描识别弱键的位置是非常有效的。3)利用泄漏瑞利波的2^<和>谐波，在1 ~ 2mm深度范围内评估了剂量疲劳裂纹的深度。这对于确定压力容器的初始疲劳裂纹深度特别有用。4)建立了非线性波传播有限元程序，通过引入特殊的接触单元来模拟裂纹表面的拍击和摩擦。通过这个模拟，我们了解了谐波产生的定量性质。5)拟提交一项键合界面评价方法及设备的专利。6)该项目对一些材料制造商感兴趣，目前正在进行两个非线性超声测量的联合项目。少

The purpose of this project is to detect nondestructively minute micro-cracks and/or disbonding in structural materials and bonded interface by using nonlinear ultrasonic waves. The main idea is to detect higher harmonics generated at micro cracks under burst ultrasonic waves of large amplitude of a few tens of nanometers. When the surfaces of minute micro-cracks and/or disbonding are repeatedly dapped or rubbed, then higher harmonics, of which frequency are integral times of the incident wave frequency, are excited.This project is composed of the followings : (a) measurement technique of 2^<nd> harmonic without bonding piezo elements on the surfaces of materials tested, (b) elimination of nonlinearity of coupling water for immersion measurement, (c) numerical simulation of 2^<nd> harmonic wave with dynamic finite element method in which contact elements are introduced to model nearly dosed cracks or interfaces.Main results obtained by this projects are summarized in the followings.1) … More A 2^<nd> harmonic measurement system has built in terms of a burst wave of large amplitude, commercial piezo transducers, and digital signal processing. This system detects A_2/A_1, the 2^<nd> harmonic amplitude ratio normalized by the incident wave amplitude, greater than 0.4% with a resolution of 0.1%.2) In immersion measurement, a transmission technique has been developed, which exclude the acoustic nonlinearity of the coupling water. This is very effective for scanning to identify the locations of weak bonds.3) With the 2^<nd> harmonic of the leaky Rayleigh wave, depth of a dosed fatigue crack is evaluated for depth range of 1-2mm. This is particularly useful for sizing of initial fatigue cracks depth in pressure vessels.4) FEM codes for nonlinear wave propagation is developed to simulate crack surface clapping and rubbing with introducing special contact elements. With this simulation, we understand quantitative nature of harmonic generation.5) A patent on evaluation method and apparatus for bond interface evaluation is going to be submitted.6) This project is interested in some material makers, and two joint projects of nonlinear ultrasonic measurement are currently running. Less