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是由于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循环载荷引起的材料损伤量的技术。为了满足这一需求，人们提出了一套新的超声无损检测技术。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，与现有的超声无损评估技术相比，其准确性、分辨率和选择性都有显著提高。这种能力在许多工程应用中都是至关重要的，包括飞机、汽车、核电站和民用基础设施。该项目开发的非线性混频技术将为现有的航空航天、机械和土木工程系统的安全和可持续运行增加一个工具。在过去的半个世纪里，超声无损检测技术得到了广泛的应用。这些技术中的绝大多数只利用了超声波的线性行为。这些线性技术在检测材料中的不连续性方面是有效的，如裂纹、空洞、界面、夹杂物等。然而，对于金属等延性材料，正是疲劳损伤的积累导致了裂纹的萌生和最终的部件失效。不幸的是，线性超声无损评估技术不能表征或量化这种损伤。为了克服现有技术的这一关键缺陷，本项目将开发基于非线性超声的新技术。具体地说，该项目将发展非线性弹性固体中混波现象的基本理论，以及利用非线性混波现象对金属材料局部疲劳损伤进行无损评估的测量技术。该项目由两项任务组成。任务1的重点是通过建立数学模型和对各种类型的波在非线性固体中的混合进行数值模拟来促进波力学知识的发展。基于从任务1获得的知识，任务2将开发新的非线性混波技术，用于无损评估金属材料和结构部件的局部疲劳损伤。

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