Multi-Dimensional Stress Quantification at Complex Loaded Structural Components with Nonlinear Rayleigh Waves

本研究的目的是开发一种新的无损检测方法。该项目将量化加载结构单元的多向应力状态，包括残余应力。提出的方法使用非线性瑞利波来评估法向和剪切方向的应力状态。假设是声弹性描述了应力和超声波之间的关系。这种方法将通过使用瑞利波来量化三种应力分量。这些波与剪切应力相互作用，并允许三个角度的超声波测量同时解决三个未知的应力值。研究涉及瑞利波传播的解析公式；数值模拟将通过室内实验进行验证。这种方法有可能适用于桥梁、核电站和其他各种结构部件。瑞利波的穿透深度取决于扰动频率。这一特性将用于量化法向和剪切应力分量。研究了一个激励频率范围，以了解剪切应力对超声波的影响，并量化了三个方向的非线性系数。将非线性超声的基本方程修改为包含剪切应力项；所得方程将用实验室实验加以验证。本课题所要测试的测量方法包括：带耦合校正的压电收发器、电磁换能器系统和压电耦合激光诱导超声波。应力水平分辨率目标为10 MPa，置信度为90%。

The goal of this research is to develop a new procedure for nondestructive testing of built structural components. The project will quantify the multi-directional state of stress of loaded structural elements including residual stresses. The proposed approach uses nonlinear Rayleigh Waves for assessing the state of stress in normal and shear directions. The hypothesis is that acoustoelasticity describes the relationship between stress and ultrasonic waves. This approach will quantify three stress components through use of Rayleigh Waves. These waves interact with shear stress and permit three angled ultrasonic measurements to solve three unknown stress values simultaneously. The research involves analytical formulations of propagation of Rayleigh Waves; the numerical simulation will be validated with laboratory experiments. This approach has the potential of applicability to a variety of structural components of bridges, nuclear power plants and others.The penetration depth of the Rayleigh wave depends on the perturbation frequency. This property will be utilized to quantify the normal and shear stress components. A range of excitation frequencies will be studied to understand the influence of shear stress on the ultrasonic waves, and quantify the nonlinearity coefficients for three directions. The basic equations of nonlinear ultrasonic will be modified to include the shear stress term; the resultant equations will be verified with the laboratory experiments. The measurement approaches to be tested in this project include piezoelectric receiver-transmitter with the coupling correction, electromagnetic transducer system and piezoelectric coupled-laser induced ultrasonic waves. The stress level resolution is targeted at 10 MPa with 90 percent confidence level.