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Effect of surface energy on the yield strength of nanoporous materials

Weixu Zhang's picture

This is a very rough manuscript but including the original material we used. Any criticism or suggestion is welcome. The only aim of this letter is to reflect the multi-effect of surface energy on material or structure in nanosize scale. Here we report the effect of surface energy on the yield strength of nanoporous materials. The conventional micromechanics method is extended to consider the surface effect and expression of effective yield surface of nanoporous materials in complex stress state is derived. It is seen that surface energy has significant effect on the yield strength of nanoporous materials, and the smaller the nanosized void, the more significant the effect of surface energy. The yield strength of nanoporous materials has size-dependent effect.

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Weixu Zhang's picture

In this manuscript we do not consider the effect of surface residual stress. Because we do not think the surface residual stress is constant during deformation process. In my own opinion, just like the thermal stress, it changes with the deformation. Unfortunately, in most of the published papers the surface residual stress is to be looked as constant. So there is no result can be used directly. So we have to derivate the residual stress field by ourself. It is not the concerning problem in this paper. So we neglected the influence of surface residual stress.
Our paper is to give a method to consider the influence of surface effect on plastic deformation of nanomaterials.

Jinxiong Zhou's picture

Hi, Weixu,

Nice to meet you in Imechanica. Very intersting research work! My question is how to describe the anisotropy of surface energy? It is well known that surface energy anisotropy plays an important role in a variety of surface phenomena.

Jinxiong Zhou

what is exactly formula and definition of surface stress?

what is the ddiffrence between surface stress and energy?

Weixu Zhang's picture

Hi Prof. Zhou
I am so happy to meet you here too. How are you now?
Yes, the anisotropy of surface energy is important. Also the surface energy depends on the crystallographic orientation. Its description is not very difficult, just like the anisotropic plate with mismatch stress, please consult
" Gurtin, M. E. & Murdoch, A. I. CONTINUUM THEORY OF ELASTIC MATERIAL SURFACES. Archive for Rational Mechanics and Analysis 57, 291-323 (1975)." ,
"R. Dingreville, J. Qu and M.Cherkaoui, Surface free energy and its effect on the elastic behavior of nano-sized particles, wires and films. Journal of the Mechanics and Physics of Solids 53 (2005) 1827–1854"
"R.E. Miller and V.B. Shenoy,Size-dependent elastic properties of nanosized structural elements, Nanotechonology 11 (2000) 139–147"

Although the description of surface energy is clear, there are still a lot of misunderstandings or confusions on the surface energy. That is why there are many conflicting results in the literatures.
Think about the surface energy very carefully and use it properly.

By the way,I wish you Merry Christmas and Happy New Year.

hi, Weixu,

Prof. Zhuping Huang published some work recently about the surface/interface energy effect on nanocomposites. His post is here. You may be interested in making comments on it.

Weixu Zhang's picture

Hi, Zhen, thank you very much for your kind reminding.

In fact, the origin of my idea in this letter is the work Prof.  Huang and his coworkers.  

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