Local enrichment of NURBS patches using a non-intrusive coupling strategy: Geometric details, local refinement, inclusion, fracture

International audienceIn this work, we apply a non-intrusive global/local coupling strategy for the modelling of local phenomena in a NURBS patch. The idea is to consider the NURBS patch to be enriched as the global model. This results in a simple, flexible strategy: first, the global NURBS patch remains unchanged, which completely eliminates the need for costly re-parametrization procedures (even if the local domain is expected to evolve); then, easy merging of a linear NURBS code with any other existing robust codes suitable for the modelling of complex local behaviour is possible. The price to pay is the number of iterations of the non-intrusive solver but we show that this can be strongly reduced by means of acceleration techniques. The main development for NURBS is to be able to handle non-conforming geometries. Only slight changes in the implementation process, including the setting up of suitable quadrature rules for the evaluation of the interface reaction forces, are made in response to this issue. A range of numerical examples in two-dimensional linear elasticity are given to demonstrate the performance of the proposed methodology and its significant potential to treat any case of local enrichment in a NURBS patch simply

Couplage non-intrusif: réanalyse locale et calcul haute performance

Le couplage non-intrusif permet de prendre en compte efficacement des modifications locales (non-linéarités, conditions limites, géométrie) dans un modèle initial linéaire pré-existant sans que ce dernier ne soit affecté. Ce concept est étendu au cas des non-linéarités apparaissant de manière généralisée à l’échelle globale. Dans ce cas un ensemble de patchs recouvre l’intégralité du domaine, et le couplage peut être assimilé à une méthode de décomposition de domaine non-linéaire s’appuyant sur un logiciel industriel séquentiel

Projection-based measurement and identification

A recently developed Projection-based Digital Image Correlation (P-DVC) method is here extended to 4D (space and time) displacement field measurement and mechanical identification based on a single radiograph per loading step instead of volumes as in standard DVC methods. Two levels of data reductions are exploited, namely, reduction of the data acquisition (and time) by a factor of 1000 and reduction of the solution space by exploiting model reduction techniques. The analysis of a complete tensile elastoplastic test composed of 127 loading steps performed in 6 minutes is presented. The 4D displacement field as well as the elastoplastic constitutive law are identified. Keywords: Image-based identification, Model reduction, Fast 4D identification, In-situ tomography measurements. INTRODUCTION Identification and validation of increasingly complex mechanical models is a major concern in experimental solid mechanics. The recent developments of computed tomography coupled with in-situ tests provide extremely rich and non-destructive analyses [1]. In the latter cases, the sample was imaged inside a tomograph, either with interrupted mechanical load or with a continuously evolving loading and on-the-fly acquisitions (as ultra-fast X-ray synchrotron tomography, namely, 20 Hz full scan acquisition for the study of crack propagation [2]). Visualization of fast transformations, crack openings, or unsteady behavior become accessible. Combined with full-field measurements, in-situ tests offer a quantitative basis for identifying a broad range of mechanical behavior.Comment: SEM 2019, Jun 2019, Reno, United State

3D digital image correlation applied to birdstrike tests

The development of new bird strike shielding materials for commercial aircrafts requires test campaigns. During these tests, measurement of the high speed deformation is needed to characterize and compare the mechanical response of the shielding samples and to correlate numerical simulations with experiments. In this work, 3D digital image correlation method is used with high speed (HSP) cameras to compute the displacement and strain fields on a large area (approximately 400mm wide) of the back side of impacted samples. Compromise on spatial resolution, frame rate of HSP camera and measurement error is discussed

Local/global non-intrusive parallel coupling for large scale mechanical analysis

The permanent increase in available computing resources can achieve more and more ambitious numerical simulations (most of the time using the finite element method). When dealing with non-linear complex models on large 3D structures, the computational cost becomes prohibitive. In this paper, we present the recent developments linked to an innovative computing method: non-intrusive coupling. Such a method allows to efficiently take into account local modifiations on an initial existing model in a non-intrusive way: the previously computed analysis is left unchanged. Large scale linear models can thus be easily computed, then localised non-linear complex models can be used to pinpoint the analysis where required on the structure. After a presentation of the scientific context and a description of non-intrusive coupling methods, we will present its application to crack growth simulation and parallel structure analysis

Non-Intrusive model coupling: A flexible way to handle local geometric and mechanical details in FEA

Computer Aided Engineering (CAE) often involves structural mechanics analysis (most of the time using the finite element method). When dealing with nonlinear complex models on large 3D structures, the computational cost becomes prohibitive. In this paper, we present the recent developments linked to an innovative computing method: non-intrusive coupling. Such a method allows to efficiently taking into account local modifications on an initial existing model in a non-intrusive way: the previously computed analysis is left unchanged. Large scale linear models can thus be easily computed, then localised nonlinear complex models can be used to pinpoint the analysis where required on the structure. After a presentation of the scientific context and a description of non-intrusive coupling methods, we will present its application to crack growth simulation and parallel structure analysis

Validation and Modeling of Aeronautical Composite Structures Subjected to Combined Loadings: the VERTEX Project. Part 1: Experimental Setup, FE-DIC Instrumentation and Procedures

The development and certification of aeronautical composite structures is still largely based on the pyramid of tests. This approach is extremely costly in terms of number of tests and design loops. Moreover, this is made up of uniaxial tests whereas the real structures are mostly subjected to combined forces. The aim of the collaborative research program "VERTEX" is to make progress towards Predictive Virtual Testing and to significantly reduce the development costs of aeronautical and space programs. In this first part, the specific methodology for multiaxial tests of aeronautical structures is presented. The concept of technical specimen and their size are justified. Then, the development of a specific test device is presented. Compression / traction, shear, internal pressure and any combination are possible. Since structural tests were complex to be instrumented, a specific method of field measurement was developed. It is based on multi-camera instrumentation and an original approach named Finite Element Stereo Digital Image Correlation (FE-SDIC). A mechanical regularization with the use of Finite Element (FE) of the optical field measurements allows to calculate the translation or rotation displacement field. Thus this measured field is used for boundary conditions of the VERTEX tests. The experimental procedure, the measurement methodologies and the calculation / test dialogue are validated on isotropic metal plates in this paper

Validation and modeling of aeronautical composite structures subjected to combined loadings: The VERTEX project. Part 2: Load envelopes for the assessment of panels with large notches

One of the important issues in the certification of composite aeronautical structures is large notches. In this paper, tests are carried out on technological specimens and under tensile, shear stresses and combined loadings using the VERTEX means presented in the first part of this publication. Strong interactions between postbuckling and propagation of cuts were observed. The FE-SDIC methodology developed specifically allows a first dialog between calculation / testing. The Discrete Ply Modeling method is able to compute the onset of failure of such complex tests. New tests responses called "envelop" are proposed and realized by following a load path that allows to validate the behavior of the notched structure for certification purposes. This methodology should eventually lead to a new vision of the tests pyramid by "Predictive Virtual Testing"

One-step deposition of nano-to-micron-scalable, high-quality digital image correlation patterns for high-strain in-situ multi-microscopy testing

Digital Image Correlation (DIC) is of vital importance in the field of experimental mechanics, yet, producing suitable DIC patterns for demanding in-situ mechanical tests remains challenging, especially for ultra-fine patterns, despite the large number of patterning techniques in the literature. Therefore, we propose a simple, flexible, one-step technique (only requiring a conventional deposition machine) to obtain scalable, high-quality, robust DIC patterns, suitable for a range of microscopic techniques, by deposition of a low melting temperature solder alloy in so-called 'island growth' mode, without elevating the substrate temperature. Proof of principle is shown by (near-)room-temperature deposition of InSn patterns, yielding highly dense, homogeneous DIC patterns over large areas with a feature size that can be tuned from as small as 10nm to 2um and with control over the feature shape and density by changing the deposition parameters. Pattern optimization, in terms of feature size, density, and contrast, is demonstrated for imaging with atomic force microscopy, scanning electron microscopy (SEM), optical microscopy and profilometry. Moreover, the performance of the InSn DIC patterns and their robustness to large deformations is validated in two challenging case studies of in-situ micro-mechanical testing: (i) self-adaptive isogeometric digital height correlation of optical surface height profiles of a coarse, bimodal InSn pattern providing microscopic 3D deformation fields (illustrated for delamination of aluminum interconnects on a polyimide substrate) and (ii) DIC on SEM images of a much finer InSn pattern allowing quantification of high strains near fracture locations (illustrated for rupture of a Fe foil). As such, the high controllability, performance and scalability of the DIC patterns offers a promising step towards more routine DIC-based in-situ micro-mechanical testing.Comment: Accepted for publication in Strai

Microfabrication directe de liens sacrificiels au sein de fibres polymériques par manipulation d'une instabilité fluidique

RÉSUMÉ Une instabilité fluidique est mise à contribution d’un procédé de microfabrication modifié afin de permettre la production de fibres directement structurées de liens sacrificiels durant la déposition, améliorant ainsi leurs propriétés mécaniques. En effet, lorsqu’un filament visqueux tombe sur une plateforme, les forces de compression axiales induisent un flambement poussant le filament à boucler sur lui-même. Lorsque l’on donne à la plateforme de déposition un mouvement de translation, l’écoulement du filament adopte différents patrons résultant en une déposition périodique et bouclante sur elle-même. Le procédé est adapté à un fluide polymérique de telle sorte que le filament visqueux durcisse. Les fibres ainsi obtenues possèdent des liens solides au noeud de chaque boucle, formés lors de la solidification. Lorsque les fibres sont soumises à des forces de traction, les noeuds brisent en premier, jouant le rôle de liens sacrificiels, tandis que les longueurs contenues dans les boucles se déplient, jouant le rôle de longueurs cachées. Les mécanismes de liens sacrificiels et longueur cachée sont connus pour améliorer la ténacité de plusieurs matériaux naturels. Le but final du projet est d’implémenter un procédé fournissant aux fibres une structure améliorant leur ténacité dès leur production. En plus de la création de nombreuses microfibres, cette maitrise a donné lieu à la participation à une conférence (IMECE Montréal 2014), à un article de conférence et à un article format lettre (soumis à Nature Materials), présenté dans le ce mémoire. La soumission a été accompagnée d’une vidéo de présentation de l’article. Les contributions ont aussi été une vidéo décrivant le procédé de fabrication et remportant la seconde place au concours vidéo « Gallery of Mechanics » de la conférence NewMech 2013, ainsi qu’une photographie démontrant la précision microscopique du procédé, remportant le concours Génie en image, Polytechnique 2014, visible en annexe. L’article soumis à Nature Materials est présenté à la suite d’une revue de littérature détaillée et de la méthodologie. L’article de conférence ainsi que la video candidate au concours NewMech sont présentés en Annexe.----------ABSTRACT A fluidic instability is involved in a microfabrication process to allow the direct manufacture of sacrificial bonds into polymeric fibers. As soon as a fluid falls onto a solid platform, it coils onto itself as a result of axial compressive forces and forms a pile of loops. If the solid platform is now translated at a given speed, the pattern of the deposition is affected, resulting in the creation of squiggly fibers with periodic patterns. As the extruded solution is polymeric, it dries and the filament becomes a removable fiber. During solidification, solid bonds are formed at the node of each loop. If the fiber is loaded in tension, bonds have to break first, playing the role of sacrificial bonds, and the loops are extended, playing the role of hidden length. Such mechanisms have been shown to enhance toughness of many natural materials. The purpose of this study is thus to produce fibers directly structured with mechanical toughing mechanisms. The presented master led to the participation to a conference (IMECE Montréal 2014) and its corresponding technical paper, the redaction of a letter format submited to Extreme Mechanics, as well as a winner photography of the “Génie en image” contest organized by École Polytechnique de Montréal and a second place at the competition “Gallery of Mechanics” organized at the conference NewMech2013. Papers and the photography are presented in this thesis, following a review of the literature and a description of the used methodology