The objective of this project was to determine the contribution from a variety of obstacles to moving dislocations to the nano-indentation stress necessary to initiate plastic flow. The obstacles are characterized by different length scales. Among these characteristic lengths, there are those associated with the material microstructure such as grain size, dislocations density, irradiation-induced defects, and those related to the size of the plastic zone beneath the indenter, or equivalently to the size of the indent. Thus, we can classify the size effects into two categories: structural size effect and indentation size effect (ISE). The underlying idea is to quantify and separate these two effects on the unirradiated material first to be able to properly isolate the contribution of the irradiation defect on the measured hardness from the tests on irradiated materials.
