Determining surface tension effect on aluminum alloy mechanical properties by computer simulation tecnhique

Metallurgy and Material Science

Material science


Аuthors

Amosov A. P.1*, Voronin S. V.2**, Loboda P. S.1***, Ledyaev M. E.2***, Chaplygin K. K.2****

1. Samara State Technical University, SSTU, 244, Molodogvardeyskaya str., Samara, 443100, Russia
2. Samara National Research University named after Academician S.P. Korolev, 34, Moskovskoye shosse, Samara, 443086, Russia

*e-mail: egundor@yandex.ru
**e-mail: voronin@ssau.ru
***e-mail: stimulator90@mail.ru
****e-mail: chapkostya96@mail.ru

Abstract

In the simplest case, any solid or liquid substance consists of atoms of the same type. A surface atom can have fr om three to nine nearest neighbors, and accordingly its energy increases by the amount, proportional to the number of missing bonds, compared to an atom inside the lattice. By virtue of this, the energy of the atoms on the surface is greater than the energy of the atoms inside the lattice. Thus, a certain excess of energy must be associated with the crystal surface, depending on the structure of this surface and called a surface tension, or surface energy.

According to L.D. Landau and A.Ya. Hohstein opinion, the surface tension is a tangential force applied to a unit length of the contour, limiting a certain area of the interface, and tended to deform a solid. Thus, the surface tension should affect the mechanical properties of the material.

The presented article proposes a dimensionless criterion Χ, characterizing the surface tension contribution to the strength of a solid:


where σs is the surface tension, N/m, σy is the conventional volumetric yield stress of the solid material, and MPa; h is the thickness of a sample in the form of a strip (foil) of a solid. The value Χ = 1 determines the critical thickness hcr of the material sample at which contribution of the surface tension to the tensilestrength of the sample becomes equal to the contribution of the bulk yield strength.

The CEM of the samples were also being compared in this work with and without accounting for the surface tension. Mechanical properties of aluminum alloy were studied with the MSC.Marc software based on the finite element method. The total number of elements was 20 thousand pieces. The finite elements represented identical parallelepipeds with eight nodes and eight integration points, which allowed solve volumetric problem with small plastic deformations. The properties of the ADT aluminum in the annealed state were being set to the models.

The obtained series of CEM samples with various thicknesses, with constant length and width, were subjected to the uniaxial tension with forces causing a stress of 50 MPa, which exceeded the bulk yield stress for this alloy, but did not exceed its tensile strength. Thus, the surface tension impact on the mechanical properties of sample models was determined, which confirmed the fact that a significant contribution of surface tension forces was observed only on samples of small thickness, comparable to the critical one.

As the result of the study, simplified equations, accounting for the surface tension forces acting only in the direction, opposing tension, for determining geometric parameters of the samples at which the influence of surface tension forces was comparable with the bulk yield strength of the material, were derived. Based on the derived dependencies for the aluminum alloy, the critical thickness of the sample was determined equal to 73.5 nm.

The results of this study allow accounting for other factors impact, such as temperature, pressure, surfactant, etc., by accounting for their effect on the surface tension magnitude.

Keywords:

surface tension, finite element modeling, virtual tests, yield strength increasing

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