The edge effect in nanoindentation

Until recently, obtaining unambiguous data from a nanoindentation measurement placed near a free edge has not been possible because the discontinuity associated with the edge introduces artifacts into the measurement. The primary consequence of a free edge is to introduce a structural compliance, C-s, into the measurement. Like the machine compliance, C-m, C-s is independent of the size of the indent and it adds to the measured unloading compliance; but unlike C-m, C-s is a function of position. Accounting for C-s in nanoindentation analyses removes the artifacts in nanoindentation measurements associated with the edge, allowing researchers to more accurately probe material properties near an edge. Expressions were obtained for the effect of the free edge on hardness and modulus measured using the Oliver-Pharr method. The theory was tested on specimens including fused silica, poly(methyl methacrylate), and a layered silicon-on-insulator specimen.