Development of A Novel Resonance Ultrasound Microscopy and Absolute Measurement of Local Elastic Constant of Micro and Nano Composites

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Resonance ultrasound microscopy has been developed for quantitatively determining the elastic constant and internal friction of local region of micro and nano composite solids. It includes a wireless and electrodeless langasite oscillator, which was driven by a noncontacting manner by the line antenna located near the oscillator. Thus, the noncontacting excitation and detection of the oscillator was made possible. The vibrational analysis determined accurately the nodal points of the oscillator, at which the oscillator was supported, making the oscillator isolated from any other acoustical contacts except for the contacting specimen at the antinode spot on the bottom surface of the oscillator through a diamond tip. Thus, the oscillator was acoustically isolated, which allowed us to determine the modulus of the contacting material from the resonance frequency change. The vibrational analysis was made to determine the effective modulus of the contacting material from the resonance frequency. The microscopy was applied to duplex stainless steels, polycrystalline copper, and NbTi/Cu composites. The effective Young modulus measured showed good agreement with the values predicted. Also, it was shown that this microscopy was useful for the nondestructive evaluation of materials. The copper specimen subjected to the creep test was used for this examination. The resonance ultrasound microscopy visualized the damaged microstructure of the copper specimen. The softened regions were observed near the grain boundaries, caused by the creep voids. Besides, the elastic constant decreased inside the grains, indicating that the softening occurred not only near the grain boundaries but also inside the grains.