Begell House Inc.
International Journal for Multiscale Computational Engineering
JMC
1543-1649
7
3
2009
Preface
vii-viii
10.1615/IntJMultCompEng.v7.i3.10
Effects of Sample Geometry on the Uniaxial Tensile Stress State at the Nanoscale
187-194
10.1615/IntJMultCompEng.v7.i3.20
Steffen
Brinckmann
Department of Materials Science, California Institute of Technology, Pasadena, CA 91125
J.-Y.
Kim
Department of Materials Science, California Institute of Technology, Pasadena, CA 91125
A.
Jennings
Department of Materials Science, California Institute of Technology, Pasadena, CA 91125
J. R.
Greer
Department of Materials Science, California Institute of Technology, Pasadena, CA 91125
nanoscale
plasticity
mechanical
tension
Uniaxial compression of micro- and nanopillars is frequently used to elicit plastic size effects in single crystals. Uniaxial tensile experiments on nanoscale materials have the potential to enhance the understanding of the experimentally widely observed strength increase. Further- more, these experiments allow for investigations into the in-strength and to help to study tension-compression asymmetry. The sample geometry might influence mechanical proper- ties, and to investigate this dependence, we demonstrate two methods of uniaxial nanotensile sample fabrication. We compare the experimentally obtained tensile stress-strain response for cylindrical and square nanopillars and provide finite element method simulation results and discuss the initiation of plastic yielding in these nanosamples.
A Study on the Collapse of Self-Similar Hardening Behavior of Nanostructures
195-204
10.1615/IntJMultCompEng.v7.i3.30
Yong
Gan
Department of Civil and Environmental Engineering, University of Missouri-Columbia, USA
Zhen
Chen
International Research Center for Computational Mechanics, State Key Laboratory of
Structural Analysis for Industrial Equipment, Department of Engineering Mechanics, Faculty
of Vehicle Engineering and Mechanics, Dalian University of Technology, Dalian 116024, China; Department of Civil and Environmental Engineering, University of Missouri, Columbia, MO 65211, USA
size effect
nanostructure
plasticity
molecular dynamics
The rate-dependent tensile responses of nanofilms and nanowires made of tungsten, copper, and gold, respectively, are investigated with the molecular dynamics method to understand the collapse of self-similar hardening (smaller is stronger) behavior of nanostructures. It is shown that such collapse is strongly dependent on material properties and specimen geometry. It is also demonstrated that the critical length scale characterizing the collapse of self-similar hardening decreases with the increase of strain rate. The plastic deformations of tungsten nanostructures and copper nanowires are in agreement with the dislocation starvation model for the self-similar hardening behavior, while the observed deformations of gold specimens and copper nanfilms imply that the phenomenon of "smaller is softer" is mainly due to the surface effects.
Deformation and Stability of Copper Nanowires under Bending
205-215
10.1615/IntJMultCompEng.v7.i3.40
Yonggang
Zheng
International Research Center for Computational Mechanics, State Key Laboratory of
Structural Analysis for Industrial Equipment, Department of Engineering Mechanics, Faculty
of Vehicle Engineering and Mechanics, Dalian University of Technology, Dalian 116024,
People's Republic of China
Hongwu
Zhang
International Research Center for Computational Mechanics, State Key Laboratory of
Structural Analysis for Industrial Equipment, Department of Engineering Mechanics, Faculty
of Vehicle Engineering and Mechanics, Dalian University of Technology, Dalian 116024,
People's Republic of China
Zhen
Chen
International Research Center for Computational Mechanics, State Key Laboratory of
Structural Analysis for Industrial Equipment, Department of Engineering Mechanics, Faculty
of Vehicle Engineering and Mechanics, Dalian University of Technology, Dalian 116024, China; Department of Civil and Environmental Engineering, University of Missouri, Columbia, MO 65211, USA
Shan
Jiang
State Key Laboratory of Structure Analysis for Industrial Equipment, Department of Engineering Mechanics, Faculty of Vehicle Engineering and Mechanics, Dalian University of Technology, Dalian 116024, China
nanowire
plastic deformation
instability
fivefold deformation twin
molecular dynamics simulation
Using molecular dynamics simulations and the embedded-atom method, the bending deformation and stability of copper nanowires are investigated in this article. It is found that the plastic deformation is mainly accommodated by the propagation of and the interaction between partial dislocations nucleated from surfaces, with twinning being a very common deformation mode. Simulation results also show that the copper nanowires exhibit a decrease of resistance against plastic deformation and tend to become homogeneous with the increase of the length, while the resistance increases with the increase of the thickness under bending. These results are consistent with those from the instability analysis based on the local Hessian matrix and suggest that the structure identification method based on the Voronoi construction can be used as a reasonable criterion for instability analysis. In addition, it is also found that two- and three-conjoint fivefold deformation twins can be formed in the quasi one-dimensional nanostructures due to the abundance of partial dislocations, stacking faults, and twins.
A Micropillar Compression Simulation by a Multiscale Plastic Model Based on 3-D Discrete Dislocation Dynamics
217-225
10.1615/IntJMultCompEng.v7.i3.50
Z. L.
Liu
Failure Mechanics Laboratory, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China
X. M.
Liu
Failure Mechanics Laboratory, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China
Zhuo
Zhuang
Failure Mechanics Laboratory, Department of Engineering Mechanics, Tsinghua University, Beijing 100084
Yuan
Gao
Applied Mechanics Laboratory, School of Aerospace, Tsinghua University, Beijing 100084 China
X. C.
You
Failure Mechanics Laboratory, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China
multiscale
discrete dislocation plasticity
finite element method
micropillar compression
dislocation starvation
In this article, a microcompression test for the Cu single-crystal micropillar containing an initial dislocation network is simulated by a multiscale computational model. This model combines a 3-D discrete dislocation dynamics (DDD) approach and a finite element method (FEM). The DDD code calculates the plastic strain induced by the slip of dislocation lines in a finite single crystal, which serves as a substitute for the constitutive relationship used in the conventional continuum mechanics. On the other hand, the displacement and stress field in crystal are calculated by FEM. In our simulations, the compression stress-strain curve ofthe micropillars can be divided into three distinct stages: a linear hardening stage, a normal plastic strain hardening stage, and a dislocation starvation hardening stage, accompanying a rather high stress level. The simulation results show that this atypical mechanical behavior is related with the effective "spiral dislocation sources" operation at the second stage and the dislocations escape from the free surfaces at the third stage. At last, the micropillar is almost dislocation-free, as observed in recent experiments.
Investigation of the Size Effect of Nickel-Base Superalloy Single Crystals Based on Strain Gradient Crystal Plasticity
227-236
10.1615/IntJMultCompEng.v7.i3.60
J. F.
Nie
Failure Mechanics Laboratory, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China
Z. L.
Liu
Failure Mechanics Laboratory, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China
X. M.
Liu
Failure Mechanics Laboratory, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China
X. C.
You
Failure Mechanics Laboratory, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China
Zhuo
Zhuang
Failure Mechanics Laboratory, Department of Engineering Mechanics, Tsinghua University, Beijing 100084
nickel-base superalloys
crystal plasticity
strain gradient
size effect
Nickel-base superalloys consist of two phases, named the phase of the nickel matrix and the ' phase of precipitates, which are dispersed uniformly in the matrix. The ' precipitates have strong effects on the mechanical properties of the alloys. In this article, the mechanism-based strain gradient crystal plasticity theory based on thermal activated theory has been developed. This theory is implemented into ABAQUS as an interface of user material (UMAT) to investigate the additional strengthening mechanism associated with the deformation gradients of the single crystal with dispersed inclusions. Four different precipitate sizes with the same volume fraction are studied using a unit-cell model of alloys. The results show a significant size effect of precipitates on nickel-base superalloys.
Atomistically Informed Mesoscale Model of Alpha-Helical Protein Domains
237-250
10.1615/IntJMultCompEng.v7.i3.70
Jeremie
Bertaud
Laboratory for Atomistic and Molecular Mechanics, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Zhao
Qin
Laboratory for Atomistic and Molecular Mechanics, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Markus J.
Buehler
Laboratory for Atomistic and Molecular Mechanics, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
hierarchical material
nanomechanics
materiomics
biological protein materials
fracture
deformation
experiment
simulation
multiscale modeling
Multiscale mechanical properties of biological protein materials have been the focal point of extensive investigations over the past decades. In this article, we present the development of a mesoscale model of alpha-helical (AH) protein domains, key constituents in a variety of biological materials, including cells, hair, hooves, and wool. Our model, derived solely from results of full atomistic simulations, is suitable to describe the deformation and fracture mechanics over multiple orders of magnitude in time- and length scales. After validation of the mesoscale model against atomistic simulation results, we present two case studies, in which we investigate, first, the effect of the length of an AH protein domain on its strength properties, and second, the effect of the length of two parallel AH protein domain arrangement on its shear strength properties and deformation mechanisms. We find that longer AHs feature a reduced tensile strength, whereas the tensile strength is maximized for ultrashort protein structures. Moreover, we find that the shearing of two parallel AHs engenders sliding, rather than AH unfolding, and that the shear strength does not significantly depend on the length of the two AHs.