Why nano indentation is used to test bulk material? I am curious why nano indentation is used? I can understand when material size goes to micros or below, conventional hardening methods can become difficult to use. However many papers say that nanoindentation has become customary to test moduli, hardness etc of materials. Why to use nanoindentation for bulk material rather than using conventional testing?
 A: This is speculation, based on working in material field many, many years ago (before nano scale testing was a Thing).
I believe that the smaller scale test can be more faithful to the underlying material properties: in essence, any large scale testing will be affected by the existence of irregularities in the material (grain boundaries, dislocations, precipitates, cracks and fissures, etc). When you probe the material on a nano(meter) scale, you are measuring the properties of such a small region that it's almost guaranteed to be defect free: and by measuring at multiple locations, you can discover the true properties by looking at the distribution of values obtained.
I'm willing to be contradicted on this.
A: I realize that this question was asked quite some time ago, but thought that I would augment the answers previously given for those that find this site with a similar question. 
Very few materials are homogeneous...from both a chemical composition and atomic structure standpoint. The mechanical properties of bulk materials are dependent on the properties of their microscale/nanoscale constituents and the interface between these constituents. Granted, you can produce a bulk material created under different processing conditions, perform a larger scale hardness test or traditional tensile test to measure modulus, and try to infer why the bulk properties are changing...or you can quantitatively measure the underlying source of the bulk response at the nanoscale. Being able to measure at this scale allows microstructural "tuning" to be performed to optimize bulk properties. Overall, the knowledge of the interaction between structure-processing-properties-performance allows for a systematic understanding of materials, rather than simply relying on phenomenological observations to further materials development. 
