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.
