Granular contact interfaces with non-circular particles

Cataloged from PDF version of article.The influence of particle geometry on the macroscopic frictional response of granular interfaces is investigated via computational contact homogenization. The particle shape is parametrized by convex superellipse geometries that require iterative closest-point projection schemes for modeling the persistent rolling contact of the particle between a rigid smooth surface and a rubber-like material. Normal and tangential forces acting on the particle are computed by the discrete element method. The non-Amontons and non-Coulomb type macroscopic frictional response of the three-body system is linked to microscopic dissipative mechanisms. Numerical investigations demonstrate rolling resistance and additionally suggest that the macroscopic friction from a complex interface particle geometry may be bound by computations that are based on simplified shapes which geometrically bound the original one. (C) 2013 Elsevier Ltd. All rights reserved

Multiscale thermomechanical contact: Computational homogenization with isogeometric analysis

Cataloged from PDF version of article.A computational homogenization framework is developed in the context of the thermomechanical contact of two boundary layers with microscopically rough surfaces. The major goal is to accurately capture the temperature jump across the macroscopic interface in the finite deformation regime with finite deviations from the equilibrium temperature. Motivated by the limit of scale separation, a two-phase thermomechanically decoupled methodology is introduced, wherein a purely mechanical contact problem is followed by a purely thermal one. In order to correctly take into account finite size effects that are inherent to the problem, this algorithmically consistent two-phase framework is cast within a self-consistent iterative scheme that acts as a first-order corrector. For a comparison with alternative coupled homogenization frameworks as well as for numerical validation, a mortar-based thermomechanical contact algorithm is introduced. This algorithm is uniformly applicable to all orders of isogeometric discretizations through non-uniform rational B-spline basis functions. Overall, the two-phase approach combined with the mortar contact algorithm delivers a computational framework of optimal efficiency that can accurately represent the geometry of smooth surface textures. Copyright (c) 2013 John Wiley & Sons, Ltd

Computational homogenization of soft matter friction: Isogeometric framework and elastic boundary layers

Cataloged from PDF version of article.A computational contact homogenization framework is established for the modeling and simulation of soft matter friction. The main challenges toward the realization of the framework are (1) the establishment of a frictional contact algorithm that displays an optimal combination of accuracy, efficiency, and robustness and plays a central role in (2) the construction of a micromechanical contact test within which samples of arbitrary size may be embedded and which is not restricted to a single deformable body. The former challenge is addressed through the extension of mixed variational formulations of contact mechanics to a mortar-based isogeometric setting where the augmented Lagrangian approach serves as the constraint enforcement method. The latter challenge is addressed through the concept of periodic embedding, with which a periodically replicated C1-continuous interface topography is realized across which not only pending but also ensuing contact among simulation cells will be automatically captured. Two-dimensional and three-dimensional investigations with unilateral/bilateral periodic/random roughness on two elastic micromechanical samples demonstrate the overall framework and the nature of the macroscopic frictional response. Copyright © 2014 John Wiley & Sons, Ltd

A mixed formulation of mortar-based contact with friction

Cataloged from PDF version of article.A classical three-field mixed variational formulation of frictionless contact is extended to the frictional regime. The construction of the variational framework with respect to a curvilinear coordinate system naturally induces projected mortar counterparts of tangential kinetic and kinematic quantities while automatically satisfying incremental objectivity of the associated discrete penalty-regularized mortar constraints. Mixed contact variables that contribute to the boundary value problem are then obtained through unconstrained, lumped or constrained recoveiy approaches, complemented by Uzawa augmentations. Patch tests and surface locking studies are presented together with local and global quality monitors of the contact interactions in two- and three-dimensional settings at the infinitesimal and finite deformation regimes. (C) 2012 Elsevier B.V. All rights reserved

On the asymptotic expansion treatment of two-scale finite thermoelasticity

Cataloged from PDF version of article.The asymptotic expansion treatment of the homogenization problem for nonlinear purely mechanical or thermal problems exists, together with the treatment of the coupled problem in the linearized setting. In this contribution, an asymptotic expansion approach to homogenization in finite thermoelasticity is presented. The treatment naturally enforces a separation of scales, thereby inducing a first-order homogenization framework that is suitable for computational implementation. Within this framework two microscopically uncoupled cell problems, where a purely mechanical one is followed by a purely thermal one, are obtained. The results are in agreement with a recently proposed approach based on the explicit enforcement of the macroscopic temperature, thereby ensuring thermodynamic consistency across the scales. Numerical investigations additionally demonstrate the computational efficiency of the two-phase homogenization framework in characterizing deformation-induced thermal anisotropy as well as its theoretical advantages in avoiding spurious size effects. (C) 2012 Elsevier Ltd. All rights reserved

Multiscale hydro-thermo-chemo-mechanical coupling: Application to alkali-silica reaction

Cataloged from PDF version of article.Alkali-Silica Reaction (ASR) is a complex chemical process that affects concrete structures and so far various mechanisms to account for the reaction at the material level have already been proposed. The present work adopts a simple mechanism, in which the reaction takes place at the micropores of concrete, with the aim of establishing a multiscale framework to analyze the ASR induced failure in the concrete. For this purpose, 3D micro-CT scans of hardened cement paste (HCP) and aggregates with a random distribution embedded in a homogenized cement paste matrix represent, respectively, the microscale and mesoscale of concrete. The analysis of the deterioration induced by ASR with the extent of the chemical reaction is initialized at the microscale of HCP. The temperature and the relative humidity influence the chemical extent. The correlation between the effective damage due to ASR and the chemical extent is obtained through a computational homogenization approach, enabling to build the bridge between microscale damage and macroscale failure. A 3D hydro-thermo-chemo-mechanical model based on a staggered method is developed at the mesoscale of concrete, which is able to reflect the deterioration at the microscale due to ASR. (C) 2013 Elsevier B. V. All rights reserved

On the optimality of the window method in computational homogenization

Cataloged from PDF version of article.The window method, where the microstructural sample is embedded into a frame of a homogeneous material, offers an alternative to classical boundary conditions in computational homogenization. Experience with the window method, which is essentially the self-consistent scheme but with a finite surrounding medium instead of an infinite one, indicates that it delivers faster convergence of the macroscopic response with respect to boundary conditions of pure essential or natural type as the microstructural sample size is increased to ensure statistical representativeness. In this work, the variational background for this observed optimal convergence behavior of the homogenization results with the window method is provided and the method is compared with periodic boundary conditions that it closely resembles. (C) 2013 Elsevier Ltd. All rights reserved

Computational thermal homogenization of concrete

Cataloged from PDF version of article.Computational thermal homogenization is applied to the microscale and mesoscale of concrete sequentially. Microscale homogenization is based on a 3D micro-CT scan of hardened cement paste (HCP). Mesoscale homogenization is carried out through the analysis of aggregates which are randomly distributed in a homogenized matrix. The thermal conductivity of this matrix is delivered by the homogenization of HCP, thereby establishing the link between micro-mesoscale of concrete. This link is critical to capture the dependence of the overall conductivity of concrete on the internal relative humidity. Therefore, special emphasis is given to the effect of relative humidity changes in micropores on the thermal conductivity of HCP and concrete. Each step of homogenization is compared with available experimental data. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved

A computational homogenization framework for soft elastohydrodynamic lubrication

Cataloged from PDF version of article.The interaction between microscopically rough surfaces and hydrodynamic thin film lubrication is investigated under the assumption of finite deformations. Within a coupled micro–macro analysis setting, the influence of roughness onto the macroscopic scale is determined using F E2-type homogenization techniques to reduce the overall computational cost. Exact to within a separation of scales assumption, a computationally efficient two-phase micromechanical test is proposed to identify the macroscopic interface fluid flux from a lubrication analysis performed on the deformed configuration of a representative surface element. Parameter studies show a strong influence of both roughness and surface deformation on the macroscopic response for isotropic and anisotropic surfacial microstructures

A mixed formulation of mortar-based frictionless contact

A class of mortar-based frictionless contact formulations is derived based on a classical three-field mixed variational framework. Within a penalty regularization complemented by Uzawa augmentations, discrete mortar constraints are naturally induced by the variational setting. Major aspects of earlier mortar approaches are obtained through constrained, lumped or unconstrained recovery procedures for the mixed kinematic and kinetic mortar quantities from their projected counterparts. Two- and three-dimensional examples at the infinitesimal and finite deformation regimes highlight the local and global quality of the contact interactions. © 2012 Elsevier B.V