Based on microindentation experiments of three different metals, Guelorget et al. [J. Mater. Res. 22, 1512 (2007)] have compared the performance of five different indentation methods on extracting material plastic properties - among them, three papers were proposed by Cao and Lu [Acta Mater. 52, 4023 (2004); J. Mater. Res. 20, 1194 (2005); J. Mech. Phys. Solids 53, 49 (2005)] and two papers were published by our group [Ogasawara et al., Scripta Mater. 54, 65 (2006); Zhao et al. Acta Mater. 54, 23 (2006)]. They argued that the performances of our techniques in [Ogasawara et al., Scripta Mater. 54, 65 (2006); Zhao et al. Acta Mater. 54, 23 (2006)] were quite poor. Here we show that Guelorget et al. [J. Mater. Res. 22, 1512 (2007)] have made quite a few mistakes and problematic steps when they handled the experiment data and performed reverse analysis. Indeed, the material plastic properties extracted from the correct procedures based on our papers [Ogasawara et al., Scripta Mater. 54, 65 (2006); Zhao et al. Acta Mater. 54, 23 (2006)] are much better and more stable than that reported in Guelorget et al. [J. Mater. Res. 22, 1512 (2007)]. Several general issues related to interpreting microindentation data and reverse analysis are also discussed, which may serve as important guidelines for similar studies in the future.
The work is supported in part by National Science Foundation (NSF) CMS-0407743, CMMI-0643726, and in part by the Department of Civil Engineering and Engineering Mechanics, Columbia University. We thank Dr. A.C. Fischer-Cripps (Fischer-Cripps Lab), Dr. W.C. Oliver (MTS), Dr. Yong Xiang (Intel), and Prof. Xiaodong Li (University of South Carolina) for helpful discussions on the data collected from nanoindentation experiments, who have confirmed the very problematic experimental setups used in Guelorget et al.1 We also thank Dr. Guelorget for sending us the original microindentation data used in Ref. 1. We are grateful to the anonymous reviewers whose valuable suggestions have significantly improved the Comment.