A Study on Nanoindentation Induced Deformation and Dislocation Mechanisms Using Molecular Dynamics Simulation
Date Issued
2006
Date
2006
Author(s)
Lai, Chia-Wei
DOI
en-US
Abstract
In this study, we study the deformation responses and dislocation mechanisms during nanoindentation into aluminum metal with three geometrically different indenters. The spherical indenter, rectangular indenter, and Berkovich indenter are employed to use in the nanoindentation simulations. Besides the dislocation microstructure developments, the elastic anisotropy of the aluminum sample for two different crystallographic planes is also discussed.
We use molecular dynamics as our modeling approach because its capability of elucidating the atomic information with high resolution can greatly help us to study the deformation process in the atomistic length scale. A general purpose materials simulation tool, the Molecular Dynamics package from Cornell Theory Center, is employed. The Ercolessi-Adams glue potential (Ercolessi and Adams 1994) is incorporated into this package to model the aluminum metal. The slip vector (Zimmerman et al. 2001) is used to detect the nucleation of dislocation defects. Two visualization tools, RasMol and PVWin, are used to visualize the deformed configuration and the dynamic deformation process. A stress definition proposed by Hardy (1982) is employed to analyze the critical mean resolved shear stress of the deformed region under the indentation site.
Based on this study, the following conclusions can be drawn: (1) The discontinuity or load drop event presenting in the load-separate displacement curve can be viewed as the signal for dislocation nucleation or defect structure transition. (2) From the elastic analysis, we find that the Ercolessi-Adams glue potential models better than . (3) The critical mean resolved stress in the deformed region for the spherical and rectangular indenter cases are in a range between 3.84GPa and 3.33GPa, which is close to the calculated theoretic shear strength for the Ercolessi-Adams glue potential, 5.28GPa. However, that value reduces to a range between 1.83GPa to 2.5GPa for the Berkovich indenter case because of the presence of a tetrahedral defect region. (4) The effective Young’s modulus of is about 66% greater than that of when the aluminum sample is subjected to indentation loading condition. (5) The plasticity behavior in the nanoindentation experiment is dominated by dislocation activities. Prosperous dislocation activities, including dislocation lock formations, dislocation cross slip and double cross slip events, are observed during the nanoindentation simulation. (6) The dislocation activities under three geometrically different indenters are observed to be significantly different. Our observations indicate that the dislocation activities are substantially affected by the indenter geometrical shape. (7) In nanoindentation simulation, the deformation behavior is different for each indenter case. (8) We successfully extend the Molecular Dynamics package to simulate the nanoindentation experiment. This general purpose software for materials simulation is proven to be extensible and flexible for specific applications.
Subjects
奈米壓印
差排理論
分子動力模擬
Nanoindentation
Dislocation theory
Molecular Dynamics Simulation
Type
thesis
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