Extracting the plastic properties of metal materials from microindentation tests: Experimental comparison of recently pu
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Cheng Liu National Laboratory for Condensed Matter Physics, Institute of Physics, Beijing 100080, China
Jian Lu Department of Mechanical Engineering, Hong Kong Polytechnic University, Hung Hom Kowloon, Hong Kong (Received 10 April 2006; accepted 27 December 2006)
Experimental verifications have been performed on three engineering metals to verify recent methods proposed for extracting stress–strain curves from indentation tests. Their sensitivity to data errors is evaluated. Finally, the factors that might cause the inaccuracy and instability of the proposed methods are discussed, providing information that can be useful for further improving these methods.
I. INTRODUCTION
Indentation has been widely used for characterizing material properties such as Young’s modulus, hardness, or yield stress. Tabor and Stilwell1–3 proposed a method for determining hardness through spherical and conical indentation, introducing the concept of representative strain.2 The first authors concerned with determining Young’s modulus through indentation were Bulychev et al.4 Later on, Doerner and Nix5 proposed a method that was improved by Oliver and Pharr.6 Consequently, indentation is now a widely used technique for performing measurements on thin films or graded materials (for instance, see Refs. 7–12). Nevertheless, it is still an issue whether the mechanical properties of a material can be obtained from indentation tests. Several methods have already been published.13–24 Giannakopoulos et al.13 have published an energy-based method for extracting plastic properties of bulk materials from instrumented indentation. Introducing a new definition of the representative strain, Dao et al.14 have proposed another method. Nevertheless, several materials, with different plastic properties, can give the same indentation curve.25–29 To obtain an unique solution, Bucaille et al.15 and Chollacoop et al.16 proposed a method using two tips of different apex angles. Cao and Lu proposed three methods. The first one uses spherical indentation.17 The second one uses sharp indentation with two
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0213 1512 J. Mater. Res., Vol. 22, No. 6, Jun 2007 http://journals.cambridge.org Downloaded: 13 Mar 2015
different tips.18 The last one is an energy-based method combined with sharp indentation.19 More recently, Ogasawara et al.21 published a method using only one sharp indentation. Zhao et al.22 proposed a method to determine not only the plastic properties, but also the elastic ones (Young’s modulus) with spherical indentation. These two articles are based on a new definition of the representative strain30 with a more physical meaning. Beghini et al.23 published a model of direct and inverse analysis. Their model is compared with real experimental indentations and seems to give good results. It needs several sets of coefficients, which are not given in their article, but can be sent on demand for each class of material. A method based on neural networks has bee
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