Indentation size effect in FCC metals: An examination of experimental techniques and the bilinear behavior

The indentation size effect (ISE) and the bilinear behavior for pure face centered cubic (FCC) metals including aluminum, nickel, silver, and 70/30 copper–zinc (α-brass) alloy using a single Berkovich indenter tip in a single test machine were investigated. The results confirmed that this behavior is mechanistic in nature and were consistent with those reported by A.A. Elmustafa and D.S. Stone [J. Mech. Phys. Solids51, 357–381 (2003)] of the ISE and the bilinear behavior using two separate indenter tips (Berkovich and Vickers) from two separate machines. Therefore, the bilinear behavior is present regardless of tip geometry or machine used. We also investigated the cause for a deviation in the continuous stiffness measurement (CSM) data from discrete data points obtained using the load control protocol at shallow depth. We conducted experiments near grain boundaries to determine if the CSM deviation at shallow depths were caused by a hardening effect due to dislocation interaction with the interface.