Browsing by Author "Wriggers, P."

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Open Access
A computational homogenization framework for soft elastohydrodynamic lubrication
(Springer, 2012) Budt, M.; Temizer, İlker; Wriggers, P.
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 FE 2-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.
Open Access
Computational thermal homogenization of concrete
(2013) Wu, T.; Temizer, I.; Wriggers, P.
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. © 2012 Elsevier Ltd. All rights reserved.
Open Access
A large deformation frictional contact formulation using NURBS‐based isogeometric analysis
(John Wiley & Sons, 2011-02-23) De, L.; Temizer, I.; Wriggers, P.; Zavarise, G.
This paper focuses on the application of NURBS-based isogeometric analysis to Coulomb frictional contact problems between deformable bodies, in the context of large deformations. A mortar-based approach is presented to treat the contact constraints, whereby the discretization of the continuum is performed with arbitrary order NURBS, as well as C0-continuous Lagrange polynomial elements for comparison purposes. The numerical examples show that the proposed contact formulation in conjunction with the NURBS discretization delivers accurate and robust predictions. Results of lower quality are obtained from the Lagrange discretization, as well as from a different contact formulation based on the enforcement of the contact constraints at every integration point on the contact surface. Copyright © 2011 John Wiley & Sons, Ltd.
Open Access
A method of two-scale chemo-thermal-mechanical coupling for concrete
(CIMNE, 2011) Wu, T.; Temizer, İlker; Wriggers, P.
The Alkali Silica Reaction(ASR) is one of the most important reasons to cause damage in cementitious constructions, which can be attributed to the expansion of hydrophilic gel produced in the reaction. In this contribution, the chemical extent is described depending on the temperature and it has influences on damage parameters. Expansions of the gel are assumed to only happen in the micropores of Hardened Cement Paste. Afterwards, the homogenization of damage in the microscale is initialized and the effective damage can be applied in the mesoscale directly. Moreover, parameter identification is implemented to extract the effective inelastic consititutive equation. In all, 3D multiscale chemo-thermo-mechanical coupled model is set up to describe the damage in the concrete due to ASR.
Open Access
Multiscale hydro-thermo-chemo-mechanical coupling: application to alkali-silica reaction
(Elsevier, 2014) Wu, T.; Temizer, I.; Wriggers, P.
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. © 2013 Elsevier B.V. All rights reserved.
Open Access
On the optimality of the window method in computational homogenization
(2013) Temizer, I.; Wu, T.; Wriggers, P.
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. © 2013 Elsevier Ltd. All rights reserved.
Open Access
Three-dimensional mortar-based frictional contact treatment in isogeometric analysis with NURBS
(2012) Temizer, I.; Wriggers, P.; Hughes, T. J. R.
A three-dimensional mortar-based frictional contact treatment in isogeometric analysis with NURBS is presented in the finite deformation regime. Within a setting where the NURBS discretization of the contact surface is inherited directly from the NURBS discretization of the volume, the contact integrals are evaluated through a mortar approach where the geometrical and frictional contact constraints are treated through a projection to control point quantities. The formulation delivers a non-negative pressure distribution and minimally oscillatory local contact interactions with respect to alternative Lagrange discretizations independent of the discretization order. These enable the achievement of improved smoothness in global contact forces and moments through higher-order geometrical descriptions. It is concluded that the presented mortar-based approach serves as a common basis for treating isogeometric contact problems with varying orders of discretization throughout the contact surface and the volume. © 2011 Elsevier B.V.