Higher Harmonic Ultrasonic Guided Waves for Structural Integrity Assessment of Infrastructure

这项研究将涉及高次谐波超声导波模式的产生，在许多金属的宏观损伤积累之前的微观结构演变。材料的基本力学问题要调查的是如何和为什么微观结构的演变和高次谐波产生相关。最近对超声导波模式相互作用的分析为理解高次谐波的产生提供了一个框架。据证实，高次谐波产生两个相互作用的导波模式，使原位表征的微观结构的演变，可靠的结构健康监测。该研究计划有四个主要组成部分：（1）识别产生累积高次谐波的入射模式，（2）选择激励方法以激励期望的入射模式，（3）研究微结构演变与高次谐波模式特征之间的相关性，（4）表征了微观结构演化和相应的高次谐波模与状态的关系，有充分记载的是，美国的基础设施正在老化，并且随着这种情况的发生，承载材料由于预期的载荷、意外的力以及环境和操作条件而退化。由于对公共安全的关注以及维护基础设施所需的数千亿美元，评估结构的当前状况，评估结构的当前和预期未来完整性，然后计划维修和更换是非常重要的。考虑到该国基础设施的复杂性，使用自主传感系统和开发尽早检测和表征材料损坏的方法是这个新兴的结构健康监测领域的关键组成部分，这最终将改变基础设施管理的物流。拟议的研究调查了非线性超声，其中在结构部件中传播的声波产生在原始线性材料中不会发生的波动，以表征在疲劳裂纹形成之前材料的变化。疲劳裂纹可能导致许多类型结构的灾难性故障;这项研究直接适用于压力容器，管道和发电，推进和化工厂的其他结构部件。

This research will relate the generation of higher harmonic ultrasonic guided wave modes to the microstructural evolution that precedes macroscale damage accumulation in many metals. The fundamental mechanics of materials issues to be investigated are how and why microstructural evolution and higher harmonic generation are correlated. Recent analysis of the interaction of ultrasonic guided wave modes provides a framework for understanding the generation of higher harmonics. It is conjectured that higher harmonic generation from two interacting guided wave modes enables in situ characterization of microstructural evolution for reliable structural health monitoring. The research plan has four main components: (1) identify incident modes that generate cumulative higher harmonics, (2) select actuation methods to activate the desired incident modes, (3) investigate the correlation between microstructure evolution and features of the higher harmonic modes, (4)characterize microstructure evolution and the corresponding higher harmonic modes in relation to state-of-the-art structural health monitoring modalities.It is well documented that the infrastructure in the United States is aging, and as that happens the load carrying materials degrade due to intended loads, unexpected forces, as well as the environmental and operating conditions. Due to concerns for public safety and the hundreds of billions of dollars necessary to maintain the infrastructure, it is extremely important to assess the current condition of structures, evaluate the current and expected future integrity of structures, and then plan repairs and replacement. Given the enormity of the infrastructure in this country, the use of autonomous sensory systems and the development of methods to detect and characterize material damage as early as possible are key components for this burgeoning field of structural health monitoring, which will eventually transform the logistics of infrastructure management. The proposed research investigates nonlinear ultrasonics, where sound waves traveling in a structural component generate wave motion that would not occur in a pristine linear material, to characterize changes in the material that precede the formation of a fatigue crack. Fatigue cracks can lead to catastrophic failure in many types of structures; this research applies directly to pressure vessels, piping, and other structural components for power generation, propulsion, and chemical plants.