An algorithm to determine the plastic properties of materials based on the loading data in single sharp indentation
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1049-AA05-03
An algorithm to determine the plastic properties of materials based on the loading data in single sharp indentation Akio Yonezu, Hiroyuki Hirakata, and Kohji Minoshima Mechanical Engineering, Osaka University, 2-1 Yamadaoka Suita, Osaka, 565-0871, Japan ABSTRACT We proposed an improved method to determine the plastic properties of a bulk material with only one sharp indenter. This method uses the data of loading curvature in an indentation curve to obtain the solution of the plastic properties. When the method yields two solutions, the indentation unloading data is employed to select the unique one. To verify the effectiveness of the proposed method, the plastic properties of four engineering materials were estimated on an experimental basis. INTRODUCTION Indentation is a useful technique to extract mechanical properties of material at micro and nano scale. Many researchers have explored the approach to determine the material constants of plastic constitutive equation, namely “plastic properties”, using instrumented indentation. Cheng et al. [1,2] proposed the dimensional analysis, which connects the parameters of indentation curve to the plastic properties. Extensive numerical calculation for indentation has been carried out to establish the dimensionless function to estimate the plastic properties of various materials [3-5]. For this purpose, they generally use indentation loading data, such as loading curvature, which is sensitive to the plastic properties. Since, Dao et al. [3] made a significant contribution that employs the idea of representative stress - strain [6] for the dimensionless function, we can obtain one representative point in the plastic region of the stress - strain curve. However, the plastic properties involve two independent material constants, thus another function with complete independence is required. Therefore, another indentation curve with a different angle of the indenter tip is required to obtain another representative point. These two points yield the plastic properties, when the material is assumed to obey the work hardening rule. This methodology is called dual indentation [4, 5]. Although dual indentation is well established and is reported to allow determination of the plastic properties accurately [4, 5], it has some disadvantages such as the impression must be made twice on the same specimen and separated by a practical distance. This makes it impossible to obtain accurate information on the limited area of interest. Therefore, some researchers proposed the indentation method with just one sharp indenter (called single indentation), to determine the plastic properties [3,7]. They directly use the dimensionless function of unloading curve, which is independent of the loading curve. However, this method may be difficult to determine accurately, since the unloading data is not sensitive to the plastic properties. Thus, it is required that another function with a parameter of loading curve is employed to improve the single indentation. In this study, we use different
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