Quasistatic component generation of ultrasonic waves and its applications in materials evaluation

Abstract

The quasistatic component (QSC) of ultrasonic wave propagation is one of the nonlinear ultrasonic phenomena that results from the interaction between ultrasound and nonlinearities in the solid materials. Owing to the low frequency and high sensitivity to microstructural changes in materials, the QSC has promising potential for developing cost-effective materials testing approaches and damage detection methods. However, most generation features of QSC have not been revealed and understood due to the complex propagation characteristics of ultrasonic guided waves. This thesis systematically investigates the QSC generation of ultrasound propagation in different solid materials and geometries. By theoretical analysis, finite element modeling, and experimental studies, the wave type, displacement direction, generation efficiency, cumulative effect, temporal shape, and mode conversion of QSC are comprehensively investigated. For thin plates, Lamb waves and shear horizontal waves are selected as primary waves for the study of QSC generation. For pipe-like structures, longitudinal modes and torsional modes are employed in the investigation. The results show that the generated QSC pulse wave in different structures by different primary waves invariantly possesses the fastest velocity and has mainly in-plane particle displacement. Other properties of QSC are also explored and confirmed to be consistent with the theory and numerical results. Based on the guidance of the present theoretical, numerical, and experimental studies, potential materials characterization and nondestructive testing/evaluation techniques and methods have been proposed. The elastic properties and damage state of many industrial materials, including advanced composite materials, have been promisingly characterized by the measurement and quantification of the nonlinear QSC response. The findings of QSC generation can pave the way for more future cost-effective nondestructive testing/evaluation and structural health monitoring technologies of ultrasound.