A unified level set based methodology for fast generation of complex microstructural multi-phase RVEs

peer reviewedIn the frame of the multi-scale computational analysis of complex materials, the generation of Representative Volume Elements (RVE) is often a crucial step. Various microstructure generation tools may be used, depending on the material to be considered, such as Discrete Element Methods (DEM), Random Sequential Addition (RSA) based methods for particulate media requiring important computation times; or Voronoï tessellation methods for polycrystalline materials. Besides being material specific, some of these methods may become unaffordable when considering complex microstructures, large inclusions numbers or high volume fractions. The present contribution presents a unified level set based methodology for complex, periodic (or not) and random RVE generations. The presented methodology allows RVE generation for particulate granular media, polycrystalline aggregates with large size distribution and arbitrary shapes, as well as for complex three-phase or poly-phase microstructures. A level set controlled Random Sequential Addition algorithm is used for particle distribution generation, allowing increasing the RSA algorithm efficiency, generating large and dense populations of arbitrary shaped inclusions with precise control on neighboring distances. Starting from this, several methods are presented to add specific realistic features to the generated RVEs. Modifications and densifications allow the distribution pattern to fit observed real samples or to present a specific spatial organization. The addition of one (or more) phase(s) obtained from the growth of the initial inclusions allows reproducing some typical microstructural patterns such as grain bridging in clayey soils, interfacial transition zones in concrete or hydrated gel in cement paste. The versatility of the proposed RVE generation method is illustrated by means of various examples, reproducing realistic microstructural arrangements of clayey soils, irregular masonry and polycrystalline aggregates with bimodal size distributions. © 2012 Elsevier B.V

Modelling of degradation‐permeability coupling in complex geomaterials.

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Generation and Analysis of open foam RVEs with sharp edges using Distance fields and Level sets

A methodology to generate Representative Volume Elements (RVEs) for open-foam cellular materials based on distance and level set functions is explained. The main focus of this work is to properly represent the geometry of the foam struts of the RVEs that are resultants of the solidification phase during manufacturing. The distance functions are defined based on the work of Sonon[1], where an arbitrary shape packing generation algorithm is introduced based on distance functions. Combinations of these functions are used to generate tessellations and extract open-foam structures with variations in the strut morphology according to the foam the RVE is being compared with, for example, the shape of cross-sections of the struts and their variation along the axis of the struts. The generated morphologies have been compared with real foam samples from existing literature to verify statistically the morphological properties like face-to-cell ratio, edge-to-face ratio and strut length distribution among others. The correlation of these properties on the initial conditions like sphere packing fraction, sphere volume distribution and periodicity of the RVEs have also been studied and are found to be in good match. Steep discontinuities in the distance functions derivatives result in the generation of jagged sharp edges, due to the use of discrete level set functions. Thus a modification in this extraction was deemed necessary and a procedure to extract geometries from multiple level set functions to reproduce such sharp edges of the struts has been incorporated in the current work. The individual cells are extracted as inclusion surfaces based on said combination of the distance functions and their modifications. The sharp edges are computed from the intersection of these inclusion surfaces. The resulting geometry can then be meshed using size functions based on curvature and narrowness and a mesh optimization inspired from [2]. The methodology to produce high quality meshes based on [3] will be outlined. The resulting FE models are easily exported for a multi-scale study to understand the effects of a elastic-plastic test by upscaling to assess the practical applications of these models by comparing with experimental data of physical samples

On advanced techniques for generation and discretization of the microstructure of complex heterogeneous materials

The macroscopic behavior of complex heterogeneous materials is strongly governed by the interactions between their elementary constituents within their microstructure. Beside experimental efforts characterizing the behaviors of such materials, there is growing interest, in view of the increasing computational power available, in building models representing their microstructural systems integrating the elementary behaviors of their constituents and their geometrical organization. While a large number of contributions on this aspect focus on the investigation of advanced physics in material parameter studies using rather simple geometries to represent the spatial organization of heterogeneities, few are dedicated to the exploration of the role of microstructural geometries by means of morphological parameter studies.The critical ingredients of this second type of investigation are (I) the generation of sets of representative volume elements ( RVE ) describing the geometry of microstructures with a satisfying control on the morphology relevant to the material of interest and (II) the discretization of governing equations of a model representing the investigated physics on those RVEs domains. One possible reason for the under-representation of morphologically detailed RVEs in the related literature may be related to several issues associated with the geometrical complexity of the microstructures of considered materials in both of these steps. Based on this hypothesis, this work is aimed at bringing contributions to advanced techniques for the generation and discretization of microstructures of complex heterogeneous materials, focusing on geometrical issues. In particular, a special emphasis is put on the consistent geometrical representation of RVEs across generation and discretization methodologies and the accommodation of a quantitative control on specific morphological features characterizing the microstructures of the covered materials.While several promising recent techniques are dedicated to the discretization of arbitrary complex geometries in numerical models, the literature on RVEs generation methodologies does not provide fully satisfying solutions for most of the cases. The general strategy in this work consisted in selecting a promising state-of-the-art discretization method and in designing improved RVE generation techniques with the concern of guaranteeing their seamless collaboration. The chosen discretization technique is a specific variation of the generalized / extended finite element method that accommodates the representation of arbitrary input geometries represented by level set functions. The RVE generation techniques were designed accordingly, using level set functions to define and manipulate the RVEs geometries. The RVE methodologies developed are mostly morphologically motivated, incorporating governing parameters allowing the reproduction and the quantitative control of specific morphological features of the considered materials. These developments make an intensive use of distance fields and level set functions to handle the geometrical complexity of microstructures. Valuable improvements were brought to the RVE generation methodologies for several materials, namely granular and particle-based materials, coated and cemented geomaterials, polycrystalline materials, cellular materials and textile-based materials. RVEs produced using those developments have allowed extensive testing of the investigated discretization method, using complex microstructures in proof-of-concept studies involving the main ingredients of RVE-based morphological parameter studies of complex heterogeneous materials. In particular, the illustrated approach offers the possibility to address three crucial aspects of those kinds of studies: (I) to easily conduct simulations on a large number of RVEs covering a significant range of morphological variations for a material, (II) to use advanced constituent material behaviors and (III) to discretize large 3D RVEs. Based on those illustrations and the experience gained from their realization, the main strengths and limitations of the considered discretization methods were clearly identified.Doctorat en Sciences de l'ingénieurinfo:eu-repo/semantics/nonPublishe

Soil water retention behavior modeling at the microstructure scale using level set based tools: influence of morphology

info:eu-repo/semantics/nonPublishe

A Level-Set based Representative Volume Element generator and XFEM simulations for textile and 3D-reinforced composites

This contribution presents a new framework for the computational homogenisation of the mechanical properties of textile reinforced composites. A critical point in such computational procedures is the definition and discretisation of realistic Representative Volume Elements. A geometrically-based weave generator is developed to produce realistic geometrical configurations of the reinforcing textile. This generator takes into account the contact conditions between the yarns in the reinforcement by means of an iterative scheme, taking into account the tension in the yarns in an implicit manner. The shape of the yarns cross sections can also be adapted as a function of the contact conditions using a level set-based post-processor. This allows a seamless transition towards an eXtended Finite Element scheme (XFEM), in which the obtained reinforcement geometry is subsequently exploited to derive the mechanical properties of the composite system using computational homogenisation.info:eu-repo/semantics/publishe

An advanced approach for the generation of complex heterogeneous and cellular materials RVEs using distance fields and level sets

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A level-set based multi-scale computiational modelling of soil lime-treatment processes

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An advanced approach for the generation of complex heterogeneous and cellular materials RVEs using distance fields and level sets

info:eu-repo/semantics/nonPublishe

XFEM-based homogenisation of the behaviour of heterogeneous materials,

info:eu-repo/semantics/publishe