Coupled Atomistic/Discrete Dislocation Simulations of Nanoindentation at Finite Temperature

[+] Author and Article Information
Behrouz Shiari

Steacie Institute for Molecular Sciences,  National Research Council of Canada, 100 Sussex Drive, Ottawa, ON, Canada K1A 0R6behrouz.shiari@nrc-cnrc.gc.ca

Ronald E. Miller

Department of Mechanical and Aerospace Engineering,  Carleton University, 1125 Colonel By Drive, Ottawa, ON, Canada K1S 5B6rmiller@mae.carleton.ca

William A. Curtin1

Division of Engineering, Box D,  Brown University, Providence RI, 02912william̱curtin@brown.edu


Corresponding author.

J. Eng. Mater. Technol 127(4), 358-368 (Jan 25, 2005) (11 pages) doi:10.1115/1.1924561 History: Received December 07, 2004; Revised January 25, 2005

Simulations of nanoindentation in single crystals are performed using a finite temperature coupled atomistic/continuum discrete dislocation (CADD) method. This computational method for multiscale modeling of plasticity has the ability of treating dislocations as either atomistic or continuum entities within a single computational framework. The finite-temperature approach here inserts a Nose-Hoover thermostat to control the instantaneous fluctuations of temperature inside the atomistic region during the indentation process. The method of thermostatting the atomistic region has a significant role on mitigating the reflected waves from the atomistic/continuum boundary and preventing the region beneath the indenter from overheating. The method captures, at the same time, the atomistic mechanisms and the long-range dislocation effects without the computational cost of full atomistic simulations. The effects of several process variables are investigated, including system temperature and rate of indentation. Results and the deformation mechanisms that occur during a series of indentation simulations are discussed.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

Schematic illustration of the solution procedure for coupled atomistic and discrete dislocation plasticity. The continuum is coupled to the atomistic region by the displacements of the atoms on the interface, uI, while the atoms are coupled to the continuum by the pad atoms whose displacements are dictated by the continuum fields.

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Figure 2

(a) Model geometry for the nanoindentation simulations. (b) Close-up of the atomistic/continuum interface. Continuum elements are dark gray. Light gray elements are used in dislocations detection but do not contribute to the energy. The actual interface between the two regions is made up of the atom/nodes shown by filled circles, while unfilled circles that lie inside the continuum region are used as a “pad” of atoms to couple the atoms to the continuum region.

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Figure 3

Time history of the atomistic region average temperature during nanoindentation. The atoms are assigned random velocities drawn from the Maxwell-Bolzmann distribution for the temperature of 100K. The constraint of zero center of mass velocity is imposed. The velocity of indenter is 30Å∕ps.

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Figure 4

Illustration of the importance of using CADD to model nanoindentation

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Figure 5

Nanoindentation load-displacement curves for three different temperatures

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Figure 6

Variation of critical depth for dislocation nucleation with increasing temperature

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Figure 7

Initial homogenous nucleation of two edge dislocation dipoles at a depth of approximately 0.86 a, where a is the half-width of the contact area between the substrate and indenter. The temperature of atomistic region is 10K and the indenter velocity is 0.05Å∕ps.

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Figure 8

Load-displacement curves for two different temperatures

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Figure 9

Variation of hardness (load divided by contact area) with increasing indentation depth at 10K

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Figure 10

Variation of hardness at maximum load versus temperature of the atomistic region

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Figure 11

Configuration of positions of the discrete dislocations and the atomic region at maximum load [(a), (b)] and after unloading [(c), (d)]

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Figure 12

Profiles of the atomistic surfaces after 38Å indentation at four different temperatures

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Figure 13

Load-displacement curves for three different velocities of indentation

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Figure 14

Variation of critical depth for dislocation nucleation with velocity of indentation

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Figure 15

Local surface plasticity under high speed indentation (400m∕s)




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