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Open AccessArticle

Boundary Layer Effect on Behavior of Discrete Models

Brno University of Technology, Faculty of Civil Engineering, Veverˇí 331/95, Brno 60200, Czech Republic
Materials 2017, 10(2), 157; https://doi.org/10.3390/ma10020157
Received: 9 December 2016 / Accepted: 6 February 2017 / Published: 10 February 2017
(This article belongs to the Special Issue Numerical Analysis of Concrete using Discrete Elements)
The paper studies systems of rigid bodies with randomly generated geometry interconnected by normal and tangential bonds. The stiffness of these bonds determines the macroscopic elastic modulus while the macroscopic Poisson’s ratio of the system is determined solely by the normal/tangential stiffness ratio. Discrete models with no directional bias have the same probability of element orientation for any direction and therefore the same mechanical properties in a statistical sense at any point and direction. However, the layers of elements in the vicinity of the boundary exhibit biased orientation, preferring elements parallel with the boundary. As a consequence, when strain occurs in this direction, the boundary layer becomes stiffer than the interior for the normal/tangential stiffness ratio larger than one, and vice versa. Nonlinear constitutive laws are typically such that the straining of an element in shear results in higher strength and ductility than straining in tension. Since the boundary layer tends, due to the bias in the elemental orientation, to involve more tension than shear at the contacts, it also becomes weaker and less ductile. The paper documents these observations and compares them to the results of theoretical analysis. View Full-Text
Keywords: boundary layer; wall effect; discrete model; elasticity; fracture; concrete boundary layer; wall effect; discrete model; elasticity; fracture; concrete
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Eliáš, J. Boundary Layer Effect on Behavior of Discrete Models. Materials 2017, 10, 157.

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