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

众所周知，大量涉及飞机、桥梁和水坝的灾难性灾难都是由于我们无法识别某些关键部件即将发生的疲劳损伤。 因此，为了提高结构和部件的安全性、可靠性、成本和性能，有必要开发能够表征和量化由循环载荷引起的材料损伤量的技术。 为了满足这一需求，一套新的超声无损评价技术已被提出。 这些新技术将具有检测金属材料局部疲劳损伤的独特能力，与现有的超声波无损评价技术相比，其精度、分辨率和选择性将大大提高。这种能力在许多工程应用中至关重要，包括飞机、汽车、核电站和民用基础设施。 本项目开发的非线性波混频技术将为我们现有的工具箱增加一个工具，用于航空航天，机械和土木工程系统的安全和可持续运行。超声波无损检测技术在过去的半个世纪得到了广泛的应用。 这些技术中的绝大多数仅利用超声的线性行为。 这些线性技术在检测材料中的不连续性（如裂纹、空隙、界面、夹杂物等）方面是有效的。然而，对于金属等韧性材料，疲劳损伤的累积会导致裂纹萌生和部件的最终失效。不幸的是，线性超声无损评价技术无法表征或量化这种损伤。 为了克服现有技术的这一关键缺点，本项目将开发基于非线性超声的新技术。具体而言，本项目将开发非线性弹性固体中的波混合现象的基本理论，以及利用非线性波混合现象对金属材料中的局部疲劳损伤进行无损评估的测量技术。该项目包括两项任务。 任务1的重点是通过建立数学模型和对非线性固体中各种波的混合进行数值模拟来提高我们的波动力学知识。 基于从任务1中获得的知识，任务2将开发新的非线性波混合技术，用于无损评估金属材料和结构部件中的局部疲劳损伤。

It is well known that a significant number of catastrophic disasters involving airplanes, bridges, and damns, for example, were due to our 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 our 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 our 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.