Abstract
Acoustic methods have been used successfully for microscale contact nondestructive evaluation, but until very recently, were not available for the nanometer scale. Noncontact submicrometer resolution ultrasonic microscopy and scanning probe microscopy (SPM) operate at higher acoustic modes and have great potential to be qualitative but face data interpretation difficulties. Nanomechanical test instruments offer nanometer scale quantitative characterization. These tools coupled with in situ SPM-type imaging and simultaneous acoustic response monitoring open new instrumentation horizons for micro/nano fracture mechanics. Both active and passive acoustic methods can be utilized to characterize a large variety of substrates and coatings. Examples of AE monitoring of nanoindentation/scratch on data storage media will be presented. Plastic deformation induced events can be separated from contact friction events by identifying AE signatures. Active ultrasonic methods can be utilized for nanoscale characterization of tribological surfaces. A friction coefficient reduction of 20% was observed on an ultrasonically excited surface during nanoscratch testing and was further investigated using post-scratch SPM-type imaging. A synergy of localized ultrasonic monitoring and nanoindentation technique can lead to the development of new and promising instrumentation for characterizing in vivo/vitro biological tissues at the molecular level. Examples on evaluating ultrasonically transmitted signal through biological samples will be discussed.
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