Title: Dislocation-based model for predicting size-scale effects on the micro and nano indentation hardness of metallic materials

Authors: Rashid K. Abu Al-Rub, Abu N.M. Faruk

Addresses: Zachry Department of Civil Engineering, Texas A&M University, College Station, TX 77843, USA. ' Zachry Department of Civil Engineering, Texas A&M University, College Station, TX 77843, USA

Abstract: In micro- and nano-indentation tests for evaluating strength and stiffness properties of engineering materials, a commonly observed phenomenon is the dependence of material properties on the indent size, also known as indentation size effect (ISE). The objective of the present work is to formulate a micro-mechanical based model based on dislocation mechanics for predicting ISE from conical or pyramidal (Berkovich and Vickers) indenters and to compare it with the most widely used Nix-Gao model. The key idea proposed here while deriving the model is a non-linear coupling between the geometrically necessary dislocations (GNDs) and the statistically stored dislocations (SSDs) that eventually allows it to simultaneously predict ISE from both micro- and nano-indentations tests on a wide range of metallic materials while the Nix-Gao model fails to do so. The work also presents a method for identifying the length scale parameter from micro- and nano-indentation experiments and also correlates it with the spacing between dislocations and thus gives a physical interpretation of the material intrinsic length scale.

Keywords: indentation size effect; ISE; microindentation; nanoindentation; geometrically necessary dislocations; GNDs; statistically stored dislocations; SSDs; length scale; hardness; strength; stiffness; modelling; dislocation mechanics; metals; metallic materials.

DOI: 10.1504/IJMSI.2010.035209

International Journal of Materials and Structural Integrity, 2010 Vol.4 No.2/3/4, pp.251 - 277

Published online: 14 Sep 2010 *

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