2014 Vol.4(5)

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A simple model for diffusion-induced dislocations during the lithiation of crystalline materials
Fuqian Yang
2014, 4(5): 051001. doi: 10.1063/2.1405101
[Abstract](74) [PDF 94KB](2)
Assuming that the lithiation reaction occurs randomly in individual small particles in the vicinity of the reaction front, a simple model of difFusion-induced dislocations was developed. The diffusion-induced dislocations are con-trolled by the misfit strain created by the diffusion of solute atoms or the phase transformation in the vicinity of the reaction front. The dislocation density is proportional to the total surface area of the "lithiated particle" and inversely pro-portional to the particle volume. The diffusion-induced dislocations relieve the diffusion-induced stresses.
Effects of vacancy defect on the tensile behavior of graphene
Xiaoyu Sun, Zuoguang Fu, Mingtan Xia, Yuanjie Xu
2014, 4(5): 051002. doi: 10.1063/2.1405102
[Abstract](67) [PDF 14464KB](1)
Graphene is the strongest material but its performance is significantly weakened by vacancy defects. We use molecular dynamics simulations to inves-tigate the tensile behavior of a graphene which contains a single vacancy defect.Our results suggest that because of the single vacancy, the fracture strength of graphene losses about 17.7%. The stress concentration around the vacancy defectleads to the destruction of nearby six-member rings structure, which forms the initial crack. The propagation direction of this crack in defective graphene is at an angel of 600 to the tensile direction initially, but then becomes perpendicular to the tensile direction.
Interplay between polarization rotation and crack propagation in PMN-PT relaxor single crystals
Fei Fang, Wenqi Jing, Wei Yang
2014, 4(5): 051003. doi: 10.1063/2.1405103
[Abstract](83) [PDF 2206KB](1)
Investigations on the interconnection between the polarization rotation and crack propagation are performed for [110]-oriented 74Pb(Mg1/3Nb2/3)O3-26PbTiO3 relaxor ferroelectric single crystal under electric loadings along [001]direction. The crystal is of predominantly monoclinic MA phase with scatter dis-tributed rhombohedral (R) phase under a moderate poling field of 900 V/mm in [001] direction. With magnitude of 800 V/mm, a through thickness crack is initi-ated near the electrode by electric cycling. Static electric loadings is then imposed to the single crystal. As the applied static electric field increases, domain switch-ing in the monoclinic MA phase and phase transition from MA to R phase occur near the crack. The results indicate that the crack features a conducting one.Whether domain switching or phase transition occurs depends on the intensity of the electric field component that is perpendicular to the applied electric field.
Numerical investigation of the influence of shear band localization on the resonant behavior in the VHCF regime
Philipp-M. Hilgendorff, Andrei Grigorescu, Martina Zimmermann, Claus-P. Fritzen, Hans-J. Christ
2014, 4(5): 051004. doi: 10.1063/2.1405104
[Abstract](80) [PDF 8538KB](1)
The monitored resonant behavior of fatigue specimens of metastable austenitic stainless steel (AISI304) is correlated with its damage accumulation in the very high cycle fatigue (VHCF) regime. The resonant behavior is stud-ied experimentally and shows a distinct transient characteristic. Microscopic ex-aminations indicate that during VHCF a localized plastic deformation in shear bands arises on the specimen surface. Hence, this work focuses on the effect of damage accumulation in shear bands on the resonant behavior of AISI304 in the VHCF regime. A microstructural simulation model is proposed that takes into account specific mechanisms in shear bands proven by experimental results.The simulation model is solved numerically using the two-dimensional bound-ary element method and the resonant behavior is characterized by evaluating the force-displacement hysteresis loop. Simulation of shear bands agrees well with microscopic examinations and plastic deformation in shear bands influences the transient characteristic of the resonant behavior.
On non-singular GRADELA crack fields
Elias C. Aifantis
2014, 4(5): 051005. doi: 10.1063/2.1405105
[Abstract](78) [PDF 97KB](1)
Abrief account is provided on crack-tip solutions that have recently been published in the literature by employing the so-called GRADELA model and its variants. The GRADELA model is a simple gradient elasticity theory involving one internal length in addition to the two Lame' constants, in an effort to eliminate elastic singularities and discontinuities and to interpret elastic size effects. The non-singular strains and non-singular (but sometimes singular or even hypersingu-lar) stresses derived this way under different boundary conditions differ from eachother and their physical meaning in not clear. This is discussed which focus on the form and physical meaning of non-singular solutions for crack-tip stresses and strains that are possible to obtain within the GRADELA model and its extensions.
Physical mechanism of the compressive response of F-actinnetworks:significance of crosslinker unbinding events
Tong Li, Dean Hu, Prasad K.D.V. Yarlagadda, Yuantong Gu
2014, 4(5): 051006. doi: 10.1063/2.1405106
[Abstract](183) [PDF 1692KB](0)
A model of crosslinker unbinding is implemented in a highly coarse-grained granular model of F-actin cytoskeleton. We employ this specific granular model to study the mechanisms of the compressive responses of F-actin networks.It is found that the compressive response of F-actin cytoskeleton has dependency on the strain rate. The evolution of deformation energy in the network indicates that crosslinker unbinding events can induce the remodelling of F-actin cytoskele-ton in response to external loadings. The internal stress in F-actin cytoskeleton can efficiently dissipate with the help of crosslinker unbinding, which could lead to the spontaneous relaxation of living cells.
Plastic deformation modelling of tempered martensite steel block structure by a nonlocal crystal plasticity model
Martin Boeff, Anxin Ma, Alexander Hartmaier
2014, 4(5): 051007. doi: 10.1063/2.1405107
[Abstract](87) [PDF 876KB](1)
The plastic deformations of tempered martensite steel representative volume elements with different martensite block structures have been investi-gated by using a nonlocal crystal plasticity model which considers isotropic and kinematic hardening produced by plastic strain gradients. It was found that pro-nounced strain gradients occur in the grain boundary region even under homo-geneous loading. The isotropic hardening of strain gradients strongly influences the global stress-strain diagram while the kinematic hardening of strain gradi-ents influences the local deformation behaviour. It is found that the additional strain gradient hardening is not only dependent on the block width but also on themmisorientations or the deformation incompatibilities in adjacent blocks.
Simulation of size effects by a phase field model for fracture
Charlotte Kuhn, Ralf Muller
2014, 4(5): 051008. doi: 10.1063/2.1405108
[Abstract](87) [PDF 231KB](2)
In phase field fracture models the value of the order parameter distin-guishes between broken and undamaged material. At crack faces the order param-eter interpolates smoothly between these two states of the material, which can be regarded as phases. The crack evolution follows implicitly from the time inte-gration of an evolution equation of the order parameter, which is coupled to the mechanical field equations. Among other phenomena phase field fracture mod-els are able to reproduce crack nucleation in initially sound materials. For a 1D setting it has been shown that crack nucleation is triggered by the loss of stabilityof the unfractured, spatially homogeneous solution, and that the stability point depends on the size of the considered structure. This work numerically investi-gates to which extend size effects are reproduced by the 2D phase field model.Exemplarily, a finite element study of the hole size effect is performed and the simulation results are compared to experimental data.
Surface effects on the persistence length of nanowires and nanotubes
Hua Liu, Hualong Song, Xiqiao Feng, Dialing Yang
2014, 4(5): 051009. doi: 10.1063/2.1405109
[Abstract](82) [PDF 141KB](1)
Surface effects on the persistence length of quasi-one-dimensionalnanomaterials are investigated by using the theory of surface elasticity and the core-shell model of nanobeams. A simple and unified expression is provided to determine the persistence length of nanowires and nanotubes with any regular polygonal cross-sections. It is demonstrated that surface effects have a distinct in-fluence on the persistence length when the characteristic sizes of materials shrink to nanometers. This work is helpful not only for understanding the size-dependent behavior of nanomaterials but also for the design of devices based on nanotubes or nanotubes.
Effective thermal conductivity of wire-woven bulk Kagome sandwich panels
Xiaohu Yang, Jiaxi Bai, Ki-Ju Kang, Tianjian Lu, Tongbeum Kim
2014, 4(5): 051010. doi: 10.1063/2.1405110
[Abstract](87) [PDF 14764KB](3)
Thermal transport in a highly porous metallic wire-woven bulk Kagome (WBK) is numerically and analytically modeled. Based on topology similarity and upon introducing an elongation parameter in thermal tortuosity, an idealized Kagome with non-twisted struts is employed. Special focus is placed upon quanti-Eying the effect of topological anisotropy ofWBK upon its effective conductivity.It is demonstrated that the effective conductivity reduces linearly as the poros-ity increases, and the extent of the reduction is significantly dependent on theorientation of WBK. The governing physical mechanism of anisotropic thermaltransport in WBK is found to be the anisotropic thermal tortuosity caused by the intrinsic anisotropic topology of WBK.
Magnetohydrodynamic process in solar activity
Jingxiu Wang, Jie Jiang
2014, 4(5): 052001. doi: 10.1063/2.1405201
[Abstract](73) [PDF 6193KB](1)
Magnetohydrodynamics is one of the major disciplines in solar physics.Vigorous magnetohydrodynamic process is taking place in the solar convection zone and atmosphere. It controls the generating and structuring of the solar mag-netic fields, causes the accumulation of magnetic non-potential energy in the solar atmosphere and triggers the explosive magnetic energy release, manifested as vi-olent solar flares and coronal mass ejections. Nowadays detailed observations in solar astrophysics from space and on the ground urge a great need for the studies of magnetohydrodynamics and plasma physics to achieve better understanding of the mechanism or mechanisms of solar activity. On the other hand, the spectac-ular solar activity always serves as a great laboratory of magnetohydrodynamics.In this article, we reviewed a few key unresolved problems in solar activity studies and discussed the relevant issues in solar magnetohydrodynamics.
Enhance limit cycle oscillation in a wind flow energy harvester system with fractional order derivatives
Cedrick A. Kitio Kwuimy, Grzegorz Litak
2014, 4(5): 053001. doi: 10.1063/2.1405301
[Abstract](86) [PDF 5687KB](0)
Advances in material science and mathematics in conjunction with tech-nological needs have triggered the use of material and electric components with fractional order physical properties. This paper considers the mathematical model of a piezoelectric wind flow energy harvester system for which the capacitance of the piezoelectric material has fractional order current-voltage characteristics. Ad- ditionally the mechanical element is assumed to have fractional order damping.The analysis is focused on the effects of order of derivatives on the appearance and characteristics of limit circle oscillations (LCO). It is obtained that, the order of derivatives to enhance the amplitude of LCO and lower the threshold condition leading to LCO. The domains of efficiency of the system are illustrated in various parameters spaces.
Stress relaxation analysis of single chondrocytes usingporohyperelastic model based on AFM experiments
Trung Dung Nguyen, Adekunle Oloyede, Yuantong Gu
2014, 4(5): 054001. doi: 10.1063/2.1405401
[Abstract](78) [PDF 3200KB](1)
Based on atomic force microscopy technique, we found that the chon-drocytes exhibits stress relaxation behavior. We explored the mechanism of this stress relaxation behavior and concluded that the intracellular fluid exuding out from the cells during deformation plays the most important role in the stress relax-anon. We applied the inverse finite element analysis technique to determine nec-essary material parameters for porohyperelastic (PHE) model to simulate stress relaxation behavior as this model is proven capable of capturing the non-linear behavior and the fluid-solid interaction during the stress relaxation of the single chondrocytes. It is observed that PHE model can precisely capture the stress re-laxation behavior of single chondrocytes and would be a suitable model for cell biomechanics.