Assessing Microstructural Damage Using Nonlinear Ultrasonics and Multiscale Numerical Modeling

超声波检测使用高频声波来确定材料的状态，而不需要侵入。该技术可应用于缺陷检测、疲劳小裂纹、材料表征等应用领域。非线性超声检测不同于线性超声检测，它考虑了声波的大振幅，因此具有检测时效钢组织变化的能力。非线性超声检测中的可测量特性受各种微结构缺陷和裂纹的类型和分布的影响。该奖项支持基础研究，以了解超声波特性与微结构损伤之间的相关性。这项研究将通过数值模拟和实验测量相结合的方式，开发一种使用超声波检测钢中损伤的范例。该研究可应用于桁架桥梁、管道、核电站等老化民用基础设施的结构健康检测，早期发现损伤并进行后续修复可以延长结构的使用寿命。这项研究的结果将使美国经济和社会受益。这项研究涉及计算力学、传感与监测和材料科学等学科。这种跨学科的方法将对科学、技术、工程和数学学科的教育产生影响。非线性超声检测通过测量高次谐波来检测微结构的变化，而从高次谐波中提取的非线性系数受损伤分布的不均匀和损伤类型的影响。虽然可以用实验方法进行评估，但在现场进行非线性超声检测时，要考虑损伤分布和类型的所有变量实际上是不可行的。本研究采用多尺度数值模拟与实验相结合的方法，对非均匀损伤分布引起的超声波变化进行了预测。包含材料非均质性和微观结构的微观模型将从微观图像中建立，以获得损伤材料的非线性特性，然后将其用于宏观尺度模型中进行损伤评估。多尺度框架将允许对材料中的微观结构变化及其对组件行为的影响进行建模。超声波信号的变化将被量化，并与通过机械测试和使用其他无损评估技术的微观结构分析表征的机械性能的变化进行比较。

Ultrasonic testing uses high frequency sound waves to determine the state of materials without intrusion. The technique can be applied to flaw detection, small cracks due to fatigue, material characterization, and other applications. Nonlinear ultrasonic testing differs from its linear counterpart on the consideration of large amplitude of sound wave; therefore it has capabilities of detecting microstructural variations in aged steel. The measurable characteristics in nonlinear ultrasonic testing are influenced by various types and distribution of microstructural defects and cracks. This award supports fundamental research to understand the correlation between ultrasonic wave characteristics and microstructural damage. The research will develop a paradigm to detect damage in steel using ultrasonic waves by combining numerical modeling and experimental measurements. The research can be applied to structural health inspection of aging civil infrastructure such as truss bridges, pipelines, nuclear power plants, etc. Early detection of damage and subsequent repairs can extend life of structures. The results of this research will benefit the U.S. economy and society. This research involves disciplines of computational mechanics, sensing and monitoring, and material science. The interdisciplinary approach will impact the education in the Science, Technology, Engineering, and Math disciplines.Nonlinear ultrasonic testing detects microstructural variations through measuring high order harmonics; however, the nonlinear coefficient extracted from high order harmonics is influenced by the heterogeneous damage distribution and the various damage types. Although they can be assessed using experimental methods, it is practically infeasible to consider all variables in damage distribution and types when conducting nonlinear ultrasonic testing in situ. The research is to predict changes in the ultrasonic waves due to heterogeneous damage distribution in steel alloys using multi-scale numerical modeling and experiments. The micro-scale model containing material heterogeneity and microstructure will be created from micrographs to obtain nonlinear properties of damaged materials, which will then be utilized in macro scale models to assess damage. The multi-scale framework will allow modeling microstructural changes in the material and their effects on the behavior of the component. The changes in ultrasonic signal will be quantified and compared with changes in mechanical properties characterized via mechanical testing and microstructural analysis using other nondestructive evaluation techniques.