Higher Harmonic Ultrasonic Guided Waves for Structural Integrity Assessment of Infrastructure

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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.