A study of the submicron indent-induced plastic deformation
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A study of the submicron indent-induced plastic deformation C. F. Robertson CEA Saclay, DTA/SRMP, 91191 Gif sur Yvette, France
M. C. Fivel GPM2, CNRS-INPG, BP46, 38402 Saint Martin d’H`eres, France (Received 6 August 1998; accepted 1 March 1999)
A new method has been developed to achieve a better understanding of submicron indent-induced plastic deformation. This method combines numerical modeling and various experimental data and techniques. Three-dimensional discrete dislocation dynamics simulation and the finite element method (FEM) were used to model the experimental conditions associated with nanoindentation testing in fcc crystals. Transmission electron microscopy (TEM) observations of the indent-induced plastic volume and analysis of the experimental loading curve help in defining a complete set of dislocation nucleation rules, including the shape of the nucleated loops and the corresponding macroscopic loading. A validation of the model is performed through direct comparisons between a simulation and experiments for a nanoindentation test on a [001] copper single crystal up to 50 nm deep.
I. INTRODUCTION
The technological need to investigate small-scale material properties has led to a considerable increase in the use of indentation techniques—hence, the development of very low load indentation machines which allow the observation and assessment of small-scale deformation mechanisms.1–6 However, the dislocation nucleation phenomenon itself is not yet fully understood, even in materials containing neither interfacial nor bulk defects,7–11 due to the heterogeneous stress field arising in the material under the loading of a sharp indenter. Recent atomistic computations have shown that under very sharp tips (with an apex radius 5–10 nm), dislocation loops are nucleated in a very complicated manner.12 However, the simulation box size is too small for direct experimental verifications of both the mechanical behavior and the dislocation microstructures. On the other hand, 3D discrete dislocation dynamics simulations can reproduce the deformation behavior of materials through the motion of populations of individual dislocations, with plastic volumes large enough for direct comparisons.13 However, this kind of modeling at a mesoscopic scale needs an initial dislocation configuration to be specified. In Sec. II, the experimental nanoindentation conditions and sample preparation are described. The corresponding mesoscale modeling is discussed, and a complete set of rules defining both the boundary conditions and the full nucleation process is given. In Sec. III, an application of the whole method to the case of a [001] copper single crystal indentation is presented. The simulated dislocation microstructure and the indent-induced plastic volume are directly compared to the experimentally observed ones. J. Mater. Res., Vol. 14, No. 6, Jun 1999
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II. NANOINDENTATION TESTING AND 3D MODELING A. Experimental methods
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