| [Gradient Plasticity ] Nanoindentation: A New Modeling Approach to an Old Measuring Technique Nanoindentation: A New Modeling Approach to an Old Measuring Technique Avraam Konstantinidis1; 1ARISTOTLE UNIVERSITY OF THESSALONIKI, Thessaloniki, Greece; PAPER: 86/Mathematics/Regular (Oral) SCHEDULED: 11:45/Sat. 26 Oct. 2019/Hermes (64/Mezz. F) ABSTRACT: Although nanoindentation has been used for more than 40 years for calculating elastic constants (modulus and hardness) of materials at the nanoscale, the test still lacks a concrete theoretical framework. The main problems of the current conceptual framework pertaining nanoindentation include: the one-dimensional consideration of a three-dimensional problem, the calculation of elastic constants after strong local plasticity, and the dependence of the calculated elastic properties on the maximum penetration depth or maximum load. Another problem is that within the current theoretical framework, the measurements acquired through the use of instruments of increasing accuracy are theoretically interpreted by semi-empirical methods, involving many assumptions. The proposed framework in which nanoindentation is considered to be an <i>inhomogeneous compression</i> is due to the tip pyramidal geometry (Berkovich, Vickers) which tries to provide solutions to the aforementioned problems. In the proposed framework, the effect of the tip geometry is modeled in a way to be deducted from the calculation of the modulus of elasticity and hardness. Preliminary results in this direction indicate that the use of gradient theory can actually eliminate the effect of tip geometry by providing values for both the elastic modulus [1] and hardness [2]. These are independent of the maximum indentation depth or load, i.e. proving that the so-called indentation size effect (ISE) is just an artifact of the specific tip geometry. References: [1] Konstantinidis A.A., Frantziskonis G., Askes H. and Aifantis E.C., The use of nanoindentation for determining internal lengths and the constitutive response of monument materials: Models and experiments, <i>J. Mechan. Behav. Mater.</i> <b>25</b>, 57-60, 2016.<br />[2] Kampouris A.K. and Konstantinidis, A., On the interpretation of the indentation size effect (ISE) through gradient theory for Vickers and Berkovich indenters, <i>J. Mechan. Behav. Mater.</i> <b>25</b>, 161-164, 2016. |
