Wave Coupling between Two Ultrasound Waveguides (Supported by ONR N00014-19-l-2098)
The research objective is to investigate wave coupling between two ultrasound waveguides, either in parallel or in series. This study is critical for realizing optical fiber based ultrasound sensor networks (OF-USNs). It is envisioned that an OF-USN can use lightweight optical fibers as ultrasound waveguides and delay lines. When bonded on a structure, a single strand of optical fiber can collect ultrasound waves at multiple locations. The successful implementation of such an OF-USN demands controlling the ultrasound waves coupled to the optical fiber and regulating these waves within the OF-USN. Therefore, understanding wave coupling between two ultrasound waveguides is a per-requisite and will be the focus of this study. The project will be carried out in three phases. First, analytical simulation models will be established to provide insights and explanations for several experimentally observed wave-coupling phenomena. Secondly, the knowledge gained will be leveraged for the design of two network components in order to achieve optimized sensor responses as well as ultrasound focusing and mode selection. Finally, two sensor multiplexing schemes will be investigated to demonstrate the OF-USNs.
Understanding fundamentals of surface-bonded piezoelectric wafer transducer for electromechanical impedance (EMI) and ultrasound shear wave monitoring of sensitization corrosion (Supported by DOD HBCU/MI Program W911NF1810459)
The project goal is to optimize ultrasound transducer design to detect and monitor sensitization corrosion in-situ. This goal be achieved by performing fundamental studies of surface-bonded piezoelectric wafer transducers (PWaTs), including 1) gaining knowledge about the mechanical properties of adhesives and their effects on the responses of bonded PWaTs; 2) bridging the gap between simulation and experiment; 3) performing physics-based studies to examine the influences of sensitization corrosions on the PWaT electromechanical impedance (EMI); 4) generating ultrasound shear waves using surface-bonded unimorph PWaTs and studying the responses of shear waves to sensitization corrosions; and 5) developing tuning strategies for PWaT arrays to generate pure ultrasound waves. This study will establish new simulation and experiment capabilities that will significantly improve our understandings about the effects of adhesive on the performance of piezoelectric wafer transducers as well as the effects of sensitization corrosion on their EMI signatures. It will introduce new transducer designs and control strategies that are geared toward increasing our capabilities of detecting and characterizing sensitization corrosion. Such capabilities could lead to a paradigm shift on the maintenance, operation, and safety assurance of navy structures.
Experiment and Simulation Study of Surface Profile Evolution for Crack Initiation Prediction
Many man-made structures fail in fatigue; some of these failures caused catastrophic disasters. Fundamental understanding of the fatigue damage process and its driving mechanism is of paramount importance to ensure safe operations of critical infrastructures such as airplanes, bridges, etc. Despite intensive researches carried out in the past decades, the basic mechanisms of fatigue damage development remain unknown, especially during crack nucleation. This is because crack nucleation occurs at the micro-scale and is sensitive to numerous microstructural features. Recently, ASTL has identified the surface topography changes as the precursor for crack nucleation in polycrystalline pure nickel. Based on this understanding, we have developed surface roughness damage indices that can reliably predict the crack nucleation site and the crack propagation path. The mechanics foundation for this empirical observation, however, is unknown. The goal of this research is therefore to reveal the mechanics foundation of the surface topography changes and crack nucleation.