Techno Press
Tp_Editing System.E (TES.E)
Login Search


You have a Free online access.
imm
 
CONTENTS
Volume 4, Number 2, June 2011
 

Abstract
The influence of surface elasticity and surface residual stress on the elastic field of an isotropic nanoscale elastic layer of finite thickness bonded to a rigid material base is considered by employing the Gurtin-Murdoch continuum theory of elastic material surfaces. The fundamental solutions corresponding to buried vertical and horizontal line loads are obtained by using Fourier integral transform techniques. Selected numerical results are presented for the cases of a finite elastic layer and a semiinfinite elastic medium to portray the influence of surface elasticity and residual surface stress on the bulk stress field. It is found that the bulk stress field depends significantly on both surface elastic constants and residual surface stress. The consideration of out-of-plane terms of the surface stress yields significantly different solutions compared to previous studies. The solutions presented in this study can be used to examine a variety of practical problems involving nanoscale/soft material systems and to develop boundary integral equations methods for such systems.

Key Words
continuum mechanics; elasticity; nanomechanics; residual stress; surface energy; surface stress; thin films.

Address
P. Intarit, T. Senjuntichai, J. Rungamornrat: Dept. of Civil Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand
R.K.N.D. Rajapakse: Faculty of Applied Sciences, Simon Fraser University, Burnaby, Canada V5A 1S6

Abstract
Mechanical behavior in nano-sized structures differs from those in macro sized structures due to surface effect. As the ratio of surface to volume increases, surface effect is not negligible and causes size-dependent mechanical behavior. In order to identify this size effect, atomistic simulations are required; however, it has many limitations because too much computational resource and time are needed. To overcome the restrictions of the atomistic simulations and graft the well-established continuum theories, the continuum model considering surface effect, which is based on the bridging technique between atomistic and continuum simulations, is introduced. Because it reflects the size effect, it is possible to carry out a variety of analysis which is intractable in the atomistic simulations. As a part of the application examples, the homogenization method is applied to micro/nano thin films with porosity and the homogenized elastic coefficients of the nano scale thickness porous films are computed in this paper.

Key Words
multiscale analysis; surface effect; homogenization; porous materials.

Address
Joonho Jeong: Interdisciplinary Program In Automotive Engineering, Seoul National University, Gwanangno 599, Sillim-9Dong, Kwanak-gu, Seoul 151-742, Korea
Maenghyo Cho: School of Mechanical and Aerospace Engineering, Seoul National University
Jinbok Choi: Metal Forming Research Group, POSCO Global R&D Center, 180-1, Songdo-dong, Yeonsu-gu, Incheon, 406-840, Korea

Abstract
We review a series of crack problems arising in the general deformations of a linearly elastic solid (Mode-I, Mode-II and Mode-III crack) and, perhaps more significantly, when the contribution of surface effects are taken into account. The surface mechanics are incorporated using the continuum based surface/interface model of Gurtin and Murdoch. We show that the deformations of an elastic solid containing a single crack can be decoupled into in-plane (Mode-I and Mode-II crack) and anti-plane (Mode-III crack) parts, even when the surface mechanics is introduced. In particular, it is shown that, in contrast to classical fracture mechanics (where surface effects are neglected), the incorporation of surface elasticity leads to the more accurate description of a finite stress at the crack tip. In addition, the corresponding stress fields exhibit strong dependency on the size of crack.

Key Words
surface elasticity; mode-I, II, III; plane deformations; anti-plane deformations; crack tip analysis; complete exact solution; Cauchy singular integro-differential equations.

Address
Chun Il Kim: Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta T6G 2G8, Canada

Abstract
In this paper we develop a fully anisotropic pressure and temperature dependent model to investigate the effect of the microstructure on the shock response of B-HMX molecular single and polycrystals. This micromechanics-based model can account for crystal orientation as well as crystallographic twinning and slip during deformation and has been calibrated using existing gas gun data. We observe that due to the high degree of anisotropy of these polycrystals, certain orientations are more favorable for plastic deformation – and therefore defect and dislocation generation – than others. Loading along these directions results in highly localized deformation and temperature fields. This observation confirms that most of the temperature rise during high rates of loading is due to plastic deformation or dislocation pile up at microscale and not due to volumetric changes.

Key Words
high rate of loading; shock; multiscale modeling; energetic crystals; β-HMX

Address
Amir R. Zamiri and Suvranu De: Mechanical, Aerospace and Nuclear Engineering Department, Rensselaer Polytechnic Institute, 110 8th St. Troy, NY 12180, USA

Abstract
The lattice strain evolution within polycrystalline solids is influenced by the crystal orientation and grain interaction. For multi-phase polycrystals, due to potential large differences in properties of each phase, lattice strains are even more strongly influenced by grain interaction compared with single phase polycrystals. In this research, the effects of the grain interaction and crystal orientation on the lattice strain evolution in a two-phase polycrystals are investigated. Duplex steel of austenite and ferrite phases with equal volume fraction is selected for the analysis, of which grain arrangement sensitivity is confirmed in the literature through both experiment and simulation (Hedstrom et al. 2010). Analysis on the grain interaction is performed using the results obtained from the finite element calculation based on the model of restricted slip within crystallographic planes. The dependence of lattice strain on grain interactions as well as crystal orientation is confirmed and motivated the need for more in-depth analysis.

Key Words
polycrystals; grain interaction; elasticity; plasticity; finite element method.

Address
Tong-Seok Han: School of Civil and Environmental Engineering, Yonsei University, Seoul 120-749, Korea

Abstract
In this study, we proposed a three-dimensional dynamic model under the diffuse interface description for the single crawling cell. From the developed model, we described the clear evolution processes for crawling neutrophil and assessed the reliable quantitative chemotactic property, which confirmed the high possibility of adequate predictions. To establish the system considering of multiple mechanisms such as, diffusion, chemotaxis, and interaction with surface, a diffuse interface model is employed.

Key Words
chemotaxis; crawling cell; interface energy; cell migration; diffuse interface model.

Address
Jihwan Song and Dongchoul Kim: Department of Mechanical Engineering, Sogang University, 1 Shinsoo-dong, Mapo-go, Seoul, Republic of Korea


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2017 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-42-828-7996, Fax : +82-42-828-7997, Email: info@techno-press.com