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 the use of multi-scale computational techniques for masonry structural computations

info:eu-repo/semantics/publishe

Computational multi-scale frameworks for the modelling of failure of masonry structures

info:eu-repo/semantics/nonPublishe

Multi-scale modeling of damage in masonry walls

The conservation of structures of the historical heritage is an increasing concern nowadays for public authorities. The technical design phase of repair operations for these structures is of prime importance. Such operations usually require an estimation of the residual strength and of the potential structural failure modes of structures to optimize the choice of the repairing techniques. Although rules of thumb and codes are widely used, numerical simulations now start to emerge as valuable tools. Such alternative methods may be useful in this respect only if they are able to account realistically for the possibly complex failure modes of masonry in structural applications.The mechanical behaviour of masonry is characterized by the properties of its constituents (bricks and mortar joints) and their stacking mode. Structural failure mechanisms are strongly connected to the mesostructure of the material, with strong localization and damage-induced anisotropy.The currently available numerical tools for this material are mostly based on approaches incorporating only one scale of representation. Mesoscopic models are used in order to study structural details with an explicit representation of the constituents and of their behaviour. The range of applicability of these descriptions is however restricted by computational costs. At the other end of the spectrum, macroscopic descriptions used in structural computations rely on phenomenological constitutive laws representing the collective behaviour of the constituents. As a result, these macroscopic models are difficult to identify and sometimes lead to wrong failure mode predictions.The purpose of this study is to bridge the gap between mesoscopic and macroscopic representations and to propose a computational methodology for the analysis of plane masonry walls. To overcome the drawbacks of existing approaches, a multi-scale framework is used which allows to include mesoscopic behaviour features in macroscopic descriptions, without the need for an a priori postulated macroscopic constitutive law. First, a mesoscopic constitutive description is defined for the quasi-brittle constituents of the masonry material, the failure of which mainly occurs through stiffness degradation. The mesoscopic description is therefore based on a scalar damage model. Plane stress and generalized plane state assumptions are used at the mesoscopic scale, leading to two-dimensional macroscopic continuum descriptions. Based on periodic homogenization techniques and unit cell computations, it is shown that the identified mesoscopic constitutive setting allows to reproduce the characteristic shape of (anisotropic) failure envelopes observed experimentally. The failure modes corresponding to various macroscopic loading directions are also shown to be correctly captured. The in-plane failure mechanisms are correctly represented by a plane stress description, while the generalized plane state assumption, introducing simplified three-dimensional effects, is shown to be needed to represent out-of-plane failure under biaxial compressive loading. Macroscopic damage-induced anisotropy resulting from the constituents' stacking mode in the material, which is complex to represent properly using macroscopic phenomenological constitutive equations, is here obtained in a natural fashion. The identified mesoscopic description is introduced in a scale transition procedure to infer the macroscopic response of the material. The first-order computational homogenization technique is used for this purpose to extract this response from unit cells. Damage localization eventually appears as a natural outcome of the quasi-brittle nature of the constituents. The onset of macroscopic localization is treated as a material bifurcation phenomenon and is detected from an eigenvalue analysis of the homogenized acoustic tensor obtained from the scale transition procedure together with a limit point criterion. The macroscopic localization orientations obtained with this type of detection are shown to be strongly related to the underlying mesostructural failure modes in the unit cells. A well-posed macroscopic description is preserved by embedding localization bands at the macroscopic localization onset, with a width directly deduced from the initial periodicity of the mesostructure of the material. This allows to take into account the finite size of the fracturing zone in the macroscopic description. As a result of mesoscopic damage localization in narrow zones of the order of a mortar joint, the material response computationally deduced from unit cells may exhibit a snap-back behaviour. This precludes the use of such a response in the standard strain-driven multi-scale scheme. Adaptations of the multi-scale framework required to treat the mesostructural response snap-back are proposed. This multi-scale framework is finally applied for a typical confined shear wall problem, which allows to verify its ability to represent complex structural failure modes.Doctorat en sciences appliquéesinfo:eu-repo/semantics/nonPublishe

Multi-scale modeling of damage in masonry structures

ix+152hlm.;29c

Flexural effects in heterogeneous structures by means of computational homogenisation

info:eu-repo/semantics/publishe

Masonry homogenization: Failure envelope predictions

info:eu-repo/semantics/publishe

Affaire Laurentide: calcul des fréquences et modes propres

Note de calculs à destination de Bagon (bureau d'études), Calcul des fréquences propres et modes propres à l'aide du logiciel SAMCEF d'une ossature en métalinfo:eu-repo/semantics/publishe

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

Multi-scale modelling of failure in heterogeneous periodic thin shells

info:eu-repo/semantics/publishe