Why monitor acoustic emissions during nanomechanical tests?

Abstract

Acoustic Emissions (AE) monitoring has been proved as an effective non-destructive technique at the macro scale. Nevertheless, it may also be employed at nano/micro scale during nanomechanical and nanotribological testing. Local mechanical properties of surfaces or micro object are routinely explored using nanoindentation, scratch test or dynamic impact tests that are evaluated based on analysis of depth-load-time records or microscopic observation of residual indents, scratch grooves or impact craters, respectively. Although these approaches have been proven to be sufficient in most cases for a variety of materials, there are many situations where they do not provide sufficient information for a complex understanding of the deformation response. On the other hand, analysis of AE signals generated during these tests may provide valuable complementary information and provide some insight into the dynamics of phenomena like cracking, phase transitions, plastic instabilities, etc. That means that the analysis of acoustic emissions provides a better understanding and more complex interpretation of the results obtained by the above-mentioned tests. The strength of the AE based method is demonstrated for optical thin films deposited on glass tested via scratch test. Combination of AE and nanoindentation will be presented for various types of glasses. The complementary analysis of the time and frequency domain will draw the potential of the AE extended approach. Especially dynamics of the failure and fracture processes will be distinguished and elucidated. In both cases the analysis of AE events will be correlated with standard approaches.