Microscale modelling and homogenization of fiber structured materials

Various phenomena occurring on the macrosscale result from physical and mechanical behaviour on the microscale [1]. For the mechanical modeling and simulation of the heterogeneous composition of fiber structured material, in addition to the material properties the contact between the fibers has to be taken into account. The material behaviour is strongly influenced by the material properties of the fiber, but also by the geometrical structure. Periodically arranged fibers like woven, knitted or plaited fabrics and randomly oriented ones like fleece can be distinguished in their arrangement. In consideration of different lengthscales the problem involves, it is necessary to introduce a multiscale approach based on the concept of a representative volume element (RVE). The macro-micro scale transition requires a method to impose the deformation gradient on the RVE by suited boundary conditions. The reversing scale transition, based on the HILL-MANDEL condition, requires the equality of the macroscopic average of the variation of work on the RVE and the local variation of the work on the macroscale [2]. For the micro-macro transition the averaged stresses have to be extracted by a homogenization scheme. From these results an effective material law can be derived. Beside the theoretical aspects, we present the stress-strain relation for RVE-models and different boundary conditions. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modelling and design optimization of textiles via homogenization

This article deals with optimization of large structures of linear elastic material with contact modeled by Robin-type boundary conditions. Homogenization is used to represent the structures as homogenous elastic bodies and is essential for formulation of the optimization problems, where optimization of the effective properties is considered. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A posteriori error majorants of the modeling errors for elliptic homogenization problems

In this paper, we derive new two-sided a posteriori estimates of the modeling errors for linear elliptic boundary value problems with periodic coefficients solved by homogenization. Our approach is based on the concept of functional a posteriori error estimation. The estimates are obtained for the energy norm and use solely the global flux of the non-oscillatory solution of the homogenized model and solution of a boundary value problem on the cell of periodicity.     

Large deviations and stochastic homogenization

Summary A general theorem is stated providing large deviations estimates for a family of measures on a topological vector space. Applications are given in the second part, where large deviations problems arising in stochastic homogenization are discussed. Another application is given in similar problems connected with Donsker's invariance principle.     

The homogenization of surfaces and boundaries

In this survey I would like to describe several homogenization issues that arise when considering surfaces, embedded in a periodic media, that satisfy some associated geometrical property like minimizing a “periodic area integral,” or that are an interphase of a flow, a flame, a drop, whose shape is influenced, again by the surrounding periodic media.     

Theoretical study and numerical simulation of textiles

We propose a new approach for developing continuum models fit to describe the mechanical behavior of textiles. We develop a physically motivated model, based on the properties of the yarns, which can predict and simulate the textile behavior. The approach relies on the selection of a suitable topological model for the patch of the textile, coupled with constitutive models for the yarn behavior. The textile structural configuration is related to the deformation through an energy functional, which depends on both the macroscopic deformation and the distribution of internal nodes. We determine the equilibrium positions of these latter, constrained to an assigned macroscopic deformation. As a result, we derive a macroscopic strain energy function, which reflects the possibly nonlinear character of the yarns as well as the anisotropy induced by the microscopic topological pattern. By means of both analytical estimates and numerical experiments, we show that our model is well suited for both academic test cases and real industrial textiles, with particular emphasis on the tricot textile.     

Scale-integration and scale-disintegration in nonlinear homogenization

This work is devoted to scale transformations of stationary nonlinear problems. A class of coarse-scale problems is first derived by integrating a family of two-scale minimization problems (scale-integration), in presence of appropriate orthogonality conditions. The equivalence between the two formulations is established by showing that conversely any solution of the coarse-scale problem can be represented as the fine-scale average of a solution of the two-scale problem (scale-disintegration). This procedure may be applied to the homogenization of several quasilinear problems, and is related to De Giorgi’s notion of Γ-convergence. As an example the homogenization of a simple nonlinear model of magnetostatics is illustrated: a two-scale minimization problem is first derived via Nguetseng’s notion of two-scale convergence, and afterwards the equivalence with a coarse-scale problem is proved.     

Probabilistic homogenization of solid foams

The present study is concerned with a numerical procedure for prediction of uncertainties in the effective properties of solid foams. The approach is based on the multiple homogenization analysis of small-scale testing volume elements. Their microstructure is defined in terms of random variables with known probability distribution. Using a discretization of the space of the random variables, the probability distribution for the effective properties can easily be determined from the homogenization results and the probability for occurrence of the underlying microstructures of the testing volume elements. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Deterministic homogenization of Vlasov equations

We address the homogenization of the Vlasov equations using the sigma-convergence method. Assuming that the electromagnetic field is strong and is highly oscillating in both space and time, we derive the homogenization result. We then study some special cases leading to already known results.     

Generalized p-FEM in homogenization

Summary. A new finite element method for elliptic problems with locally periodic microstructure of length is developed and analyzed. It is shown that the method converges, as , to the solution of the homogenized problem with optimal order in and exponentially in the number of degrees of freedom independent of . The computational work of the method is bounded independently of . Numerical experiments demonstrate the feasibility and confirm the theoretical results. Received September 11, 1998 / Published online April 20, 2000     

Multiscale convergence and reiterated homogenization of parabolic problems

Reiterated homogenization is studied for divergence structure parabolic problems of the form u /t–div (a(x,x/,x/²,t,t/ ^k)u )=f. It is shown that under standard assumptions on the function a(x, y ₁,y ₂,t,) the sequence {u } of solutions converges weakly in L ² (0,T; H ₀ ¹ ()) to the solution u of the homogenized problem u/t– div(b(x,t)u)=f.This revised version was published online in April 2005 with a corrected missing date string.     

Integro-differential Burgers equation. Solvability and homogenization

We consider the integro-differential Burgers equation which appears in nonlinear acoustics. The integral term in the right-hand side describes the relaxation (memory) effects. The global existence and uniqueness of solution is proved. The smoothness of the solution is studied.In the case when the coefficients of the equation rapidly oscillate, we replace it by the homogenized equation with constant coefficients and prove the error estimates.     

Recent results on dislocations dynamics and homogenization

In this note, we present recent results about the homogenization of systems of particles with two-body interactions, describing dislocation dynamics. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ergodic theory and appication to nonconvex homogenization

We establish some ergodic theorems with the view to obtaining a convergence result of sequences of random Radon measures. We also give an application in stochastic homogenization of nonconvex integral functionals.     

Multi-scale computational homogenization: Trends and challenges

In the past decades, considerable progress had been made in bridging the mechanics of materials to other disciplines, e.g. downscaling to the field of materials science or upscaling to the field of structural engineering. Within this wide context, this paper reviews the state-of-the-art of a particular, yet powerful, method, i.e. computational homogenization. The paper discusses the main trends since the early developments of this approach up to the ongoing contributions and upcoming challenges in the field.     

On homogenization of time-dependent random flows

We study a diffusion with a random, time dependent drift. We prove the invariance principle when the spectral measure of the drift satisfies a certain integrability condition. This result generalizes the results of [13, 7]. Received: 25 February 2000 / Revised version: 11 December 2000 /?Published online: 14 June 2001     

Random homogenization of an obstacle problem

We study the homogenization of an obstacle problem in a perforated domain, when the holes are periodically distributed and have random shape and size. The main assumption concerns the capacity of the holes which is assumed to be stationary ergodic.