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Item type:Publication, Access status: without files , Full-field multi-scale analyses embedding fiber-matrix interfaces in short fiber reinforced thermoplasticsThis contribution presents a comprehensive full-field multi-scale modeling strategy for Short Fiber Reinforced Thermoplastics (SFRTs), with a particular focus on degradation at the fiber-matrix interfaces. The proposed approach combines nonlinear matrix behavior, cohesive interface degradation, and complex, large-scale randomized periodic Representative Volume Elements (RVEs) whose fiber orientations are derived from an experimentally determined Orientation Distribution Function (ODF). By integrating these aspects within a single framework, the model captures a level of mechanical and microstructural complexity that is rarely addressed in existing SFRT simulations. The model is applied to PA66GF30 to investigate how interface properties influence the macroscopic response of the composite in connection with the development of local damage mechanisms. Interface parameters are calibrated to reproduce experimental results, leading to good agreement with the measured overall behavior. In addition, the predicted local damage patterns are consistent with mechanisms reported in the literature, highlighting the ability of the approach to link interface degradation, microstructural morphology, and overall SFRT behavior.Publicationtype: Journal Article38 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Simultaneous optimization of composite shells, metallic components and their jointsThis paper presents an approach for the simultaneous topology optimization of an isotropic (e.g. metallic) component, the layup optimization of a composite part and the search for the optimized position of joints between the parts. Within a gradient-based optimization, a failure criterion for the composite acts as a constraint. The constraint's gradients with respect to fiber orientations, pseudo densities of the isotropic elements, and joint positions are presented. As a demonstrative example, the load introduction into an isotropic component attached to a composite plate is analyzed. The results reveal a significant influence of the considered constraint on the optimized overall design.Publicationtype: Journal Article37 32 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Realistic microstructural modeling of supercrystalline oleic acid nanocomposites(Elsevier, 2025-06-10); ; ; ; Supercrystalline nanocomposites, with their growing range of applications, present a significant challenge in understanding their structural behavior. These materials, composed of organically surface-functionalized inorganic nanoparticles arranged in periodic structures, exhibit superlattice imperfections, such as particle size scatter and superlattice vacancies, that emerge during fabrication. The mechanical effects of these defects, particularly particle size scatter and point defects, remain poorly understood due to experimental limitations. This study investigates these effects through advanced numerical modeling. A generalized Maxwell model is employed to model the oleic acid layer, with parameter values determined via inverse analysis. Subsequently, statistically equivalent periodic unit cells (SEPUCs) are used to simulate the impact of particle size scatter and point defects. Simulations reveal that nanocomposite mechanical properties, including stiffness, creep resistance, and plasticity, are highly influenced by particle distribution and the overlap volume of the organic interface. Conversely, point defects (superlattice vacancies) exhibit a negligible impact on the overall mechanical behavior. Furthermore, the material becomes increasingly isotropic with greater particle size scatter. These findings provide critical insights for the future design of these materials.Publicationtype: Journal Article71 20 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Simultaneous optimization of composite plates, metallic components and their joints(2024-06-04); ; This contribution presents an approach for the simultaneous topology optimization of an isotropic (e.g. metallic) part, the layup optimization of a composite part, and the search for the optimized position of the joints between the two parts. For that, the approach presented in [1] is extended by the optimization of composite parts. The joints are modelled by spring elements, where the loads of their reference points are distributed over a circular pattern. The degrees of freedom of these patterns are coupled to the connected parts through the shape functions of the parts’ elements. For the topology optimization, the pattern is considered as non-design space by projecting the joint pattern on the density field. The design variables considered in this optimization are the (pseudo) densities of the isotropic parts, the fiber orientations in each element and ply of the composite parts, as well as the positions of the reference points of the joint nodes. Since a gradient-based optimization algorithm is employed, the gradients of objective and constraint functions are derived with respect to all design parameters. The results show that an individual optimization of one part may be critical for the performance of the connected part and hence, worsens the overall performance. The proposed simultaneous optimization approach however allows to efficiently improve the performance of the assembly of parts.Publicationtype: Conference Presentation85 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Microstructure generation and full-field multi-scale analyses for short fiber reinforced thermoplastics : application to PA66GF compositesShort Fiber Reinforced Thermoplastics (SFRTs) like PA66GF composites are highly heterogeneous materials with a rather complex microstructure such that the characterization and the prediction of their mechanical behavior remain quite challenging. So far, most of the research efforts have employed phenomenological and mean-field multi-scale models to deal with SFRTs. The present contribution rather focuses on a full-field multi-scale approach that incorporates advanced techniques in terms of microstructural representation and material modeling, allowing a deep insight of the dominating deformation mechanisms occurring in PA66GF composites. The proposed approach is based on an automatic periodic mesh generation algorithm for matrix-inclusion Representative Volume Elements (RVE) with randomly positioned fibers that follow a given Orientation Distribution Function (ODF). At the microscopic scale, while the fibers are assumed to be elastic, the behavior of the thermoplastic matrix is described by a phenomenological multi-mechanism constitutive model accounting for viscoelasticity, viscoplasticity and ductile damage. It results an advanced multi-scale model that enables to visualize the local deformation and degradation mechanisms occurring at the microscopic scale while simultaneously analyzing their influence on the macroscopic response of the composite upon monotonic, persistent and cyclic loading. The potential of the proposed approach is further evaluated by comparing the predicted responses against experimental data.Publicationtype: Journal Article49 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Génération de microstructures et analyses multi-échelles à champs complets pour les composites thermoplastiques renforcés de fibres courtes(HAL science ouverte, 2023-07-03); ; ; Afin d’apporter un maxinmun d’éléments de compréhension quant au comportement mécanique des composites thermoplastiques renforcés de fibres courtes, la présente contribution propose une démarche multi-échelle par champs complets. Pour ce faire, des maillages de VER (Volumes Élémentaires Représentatifs) ont été générés avec un positionnement aléatoire des fibres tandis que leurs orientations sont distribuées selon une ODF (Orientation Distribution Function). Ces VERs présentent une périodicité par construction assurant ainsi une transition d’échelle par homogénéisation périodique. Le comportement à l’échelle macroscopique est ainsi déterminé à partir de simulations par éléments finis de ces VERs, intégrant les lois de comportement spécifiques des constituants et plus particulièrement celui de la matrice thermoplastique décrit ici par un modèle viscoélastique-viscoplastique avec endommagement ductile. L’approche proposée permet ainsi de visualiser les mécanismes locaux de déformation et de dégradation et d’en analyser l’influence sur la réponse macroscopique du composite lors de chargements monotones, persistants et cycliques.Publicationtype: Conference Paper39 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Computational micromechanics of matrix-inclusion composites(2019); This thesis is concerned with aspects of the computational retrievement of macroscopic material responses and investigations of the microscopic deformation behavior of random matrix-inclusion composites. To this end, the focus lies on the representative volume element (RVE) approach in the scope of finite element analyses and its applicability and integration into engineering practice. The artificial random generation of the microstructural geometry, in a periodic and non-periodic manner, is established by studying and enhancing existing methods such as the random sequential adsorption method or collective rearrangement methods for cubic RVEs. Based on distance computations between two inclusions, the non-overlap requirement, which is characteristic for matrix-inclusion composites, is ensured for ellipsoidal, capsular, cylindrical and convex polyhedral inclusion shapes. To comply with the state-of-the-art approach that utilizes fully periodic RVEs featuring a periodic topology, a periodic discretization and periodic boundary conditions (PBC), a new algorithm that automatically generates periodic meshes is developed. The algorithm systematically combines various meshing tools in an efficient and robust way. Special emphasis is placed on the discretization procedure to maintain a high quality mesh with as few elements as possible, thus, manageable for computer simulations applicable to high volume concentrations, high number of inclusions and complex inclusion geometries. Examples elucidate the ability of the proposed approach to efficiently generate large RVEs with a high number of anisotropic inclusions but still maintaining a high quality mesh and a low number of elements. Since the generation of such a state-of-the-art RVE can significantly reduce the overall efficiency in multiscale finite element simulations, a benchmark study that investigates possible relaxations to this cumbersome task is performed. In particular, the RVE size, periodic and non-periodic RVE topologies, different discretization variants and various types of boundary conditions that either require periodicity or do not require periodicity of the underlying discretization are benchmarked. Approximate periodic boundary conditions are discussed in detail. The benchmark study proves that a fully periodic topology and mesh discretization with periodic boundary conditions is not necessary in order to identify effective macroscopic material parameters for technologically relevant composites. Eventually, the gathered methodologies are applied to model a modern high-tech polymer nanocomposite. By utilizing a sophisticated material model for the polymeric matrix, the entropic and energetic deformation regime can be represented in a physically meaningful way. Furthermore, the explicit consideration of the matrix-inclusion interface failure via a cohesive zone model accounts for the non-negligible surface effects. Comparisons with experiments underline the predictive character of the modeling approach and allow for investigations of local deformation mechanisms.Publicationtype: Doctoral Thesis667 358 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Automatic generation and discretization of fully periodic representative volume elements of plain woven composites(2018-12-01); ; This paper introduces an efficient and simple method to automatically generate and mesh geometrically parametrized representative volume elements for plain woven fiber-reinforced composites. The presented approach is capable of generating representative volume elements with 10%–55% fiber volume fraction. The practical feasibility of the model is demonstrated on numerical examples for isotropic and anisotropic tow materials which are compared to analytical solutions.Publicationtype: Journal Article274 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Finite element simulation of pole vaultingPole vaulting is one of the most spectacular disciplines in athletics. The evolution of world record heights is strongly influenced by the development of advanced poles and subsequent materials. Employing advanced, load-adjusted composites has resulted in a steady increase of the world record height. This study provides a framework for finite element simulations of pole vaulting with focus on the initial and boundary conditions as well as finite element choices. The influence of the pole bending stiffness on the achievable height is systematically simulated. Higher effective bending stiffness leads to higher pole vaulting heights. However, if a certain stiffness is exceeded, the vaulter will not be able to bend the pole enough which leads to failed attempts.Publicationtype: Journal ArticleScopus© Citations 7 316 610 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Generation of 3D representative volume elements for heterogeneous materials: a review(Elsevier, 2018); ; ; ; This work reviews state of the art representative volume element (RVE) generation techniques for heterogeneous materials. To this end, we present a systematic classification considering a wide range of heterogeneous materials of engineering interest. Here, we divide heterogeneous solids into porous and non-porous media, with 0 < void volume fraction < 1 and void volume fraction = 0, respectively. Further subdivisions are realized based on various morphological features. The corresponding generation methods are classified into three categories: (i) experimental methods targeting reconstruction through experimental characterization of the microstructure, (ii) physics based methods targeting simulation of the physical process(es) responsible for the microstructure formation and evolution, and (iii) geometrical methods concentrating solely on mimicking the morphology (ignoring the physical basis of the microstructure formation process). These comprise of various mathematical tools such as digital image correlation, tessellation, random field generation, and differential equation solvers. For completeness, relevant up-to-date software tools, used at various stages of RVE generation – either commercial or open-source – are summarized. Considered methods are reviewed based on their efficiency and predictive performance with respect to geometrical and topological properties of the microstructures.Publicationtype: Journal ArticleScopus© Citations 337 861 3104