Collaborative Research: Nonlinear Ultrasonic Wave Mixing Techniques for Detecting Localized Fatigue Damage in Metallic Materials

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It is well known that a significant number of catastrophic disasters involving airplanes, bridges, and damns, for example, were due to the inability to identify impending fatigue damage of certain critical components. Therefore, in order to improve the safety, reliability, cost, and performance of structures and components, it is necessary to develop techniques that are capable of characterizing and quantifying the amount of material damage induced by cyclic loading. To meet this need, a suite of new ultrasonic nondestructive evaluation techniques have been proposed. These new techniques will have the unique capability of detecting localized fatigue damage in metallic materials with dramatically improved accuracy, resolution and selectivity over existing ultrasonic nondestructive evaluation techniques. Such capabilities are critical in many engineering applications including aircraft, automotive vehicles, nuclear power plants and civil infrastructures. The nonlinear wave mixing technique developed in this project will add one more tool to the existing toolbox for safe and sustainable operation of aerospace, mechanical and civil engineering systems. Ultrasonic nondestructive evaluation techniques have been used extensively during the last half century. The vast majority of these techniques utilize only the linear behavior of the ultrasound. These linear techniques are effective in detecting discontinuities in the materials such as cracks, voids, interfaces, inclusions, etc. However, for ductile materials such as metals, it is the accumulation of fatigue damage that leads to crack initiation and eventual failure of the component. Unfortunately, linear ultrasonic nondestructive evaluation techniques are incapable of characterizing or quantifying such damage. To overcome this critical shortcoming of the existing technologies, new techniques based on nonlinear ultrasound will be developed in this project. Specifically, the project will develop the fundamental theories for the wave mixing phenomena in nonlinear elastic solids, and the measurement techniques for nondestructive evaluation of localized fatigue damage in metallic materials by utilizing the nonlinear wave mixing phenomena. The project consists of two tasks. Task 1 focuses on advancing knowledge of wave mechanics by developing mathematical models and conducting numerical simulations of the mixing of various types of waves in nonlinear solids. Based on the knowledge gained from Task 1, Task 2 will develop novel nonlinear wave mixing techniques for nondestructive evaluation of localized fatigue damage in metallic materials and structural components.