다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Overview of constitutive laws, kinematics, homogenization and multiscale methods in crystal plasticity finite-element modeling: Theory, experiments, applications

X-ray computer tomography (CT) is fast becoming an accepted tool within the materials science community for the acquisition of 3D images. Here the authors review the current state of the art as CT transforms from a qualitative diagnostic tool to a quantitative one. Our review considers first the image acquisition process, including the use of iterative reconstruction strategies suited to specific segmentation tasks and emerging methods that provide more insight (e.g. fast and high resolution imaging, crystallite (grain) imaging) than conventional attenuation based tomography. Methods and shortcomings of CT are examined for the quantification of 3D volumetric data to extract key topological parameters such as phase fractions, phase contiguity, and damage levels as well as density variations. As a non-destructive technique, CT is an ideal means of following structural development over time via time lapse sequences of 3D images (sometimes called 3D movies or 4D imaging). This includes information nee...

https://www.tandfonline.com/doi/pdf/10.1179/1743280413Y.0000000023

Quantitative X-ray tomography

The main purpose of this study is to better understand the relationship between the microstructure of foamed polymer and mechanical properties. X-Ray tomography was performed on polypropylene foam specimens machined from injected plates. These plates were obtained for different thicknesses and exhibit different microstructure morphologies. The tomography scans were first digitalized and meshed. Then, numerical simulations were performed on representative volume elements (RVEs) to get homogeneous mechanical property of the material using a parallel C++ library Cimlib developed at CEMEF. Numerical methods described in this study focused on immerged or body-fitted strategy (FE context - level set framework - meshing adaptation) for exact and statistical RVEs generation. The numerical results were compared to experimental testing performed under tension and compression at different strain rates using image correlation. Good agreement was observed between simulations performed at the mesoscale and experimental tests carried out at the macroscale for both real and statistical RVEs. This methodology opens a way for the development of digital materials designed for specific mechanical properties.

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Generation and homogenization of foamed polymer RVEs: microstructure-mechanical properties relationship

Mean field (MF) models of dynamic recrystallization (DRX) emerged in the last decades with the intention to implicitly describe the microstructure by considering grains sets as spherical classes. These models have the advantage to provide accurate results in terms of macroscopic results such as recrystallized fraction or grain size but also to provide additional information in terms of grain size distribution and dislocation density distribution [1,2,3,4]. In parallel, finer approaches called full field (FF) models have emerged in the last decades. These approaches consider a complete description of the microstructure topology at the polycrystal scale [5]. A review of the most significant numerical methods can be found in [6].Several DRX models based on a full field approach can already be found in the literature [7,8,9]. Although literature already provides a large number of papers on full-field DRX models, major drawbacks are either they are developed in 2D and/or they only consider small deformations (< 20%). In the present work, a 3D model based on the level-set method in a FE framework is employed to model the DRX phenomenon in austenitic stainless steel 304L at large deformations. The level-set approach coupled to a remesher provides an accurate tracking of interfaces (i.e. grain boundaries) all along the simulation while mean field laws are used for the nucleation and work hardening mechanisms. A first part of this work is dedicated to a presentation of the level-set approach and the constitutive equations of this model. That part is followed by a sensibility study concerning the choice of the initial number of grains and elements so that the model correctly describes experimental results on 304L. The subsequent part presents a comparison between an enriched DRX mean field models [2] and experimental results. Some remarks about the choice of use either a mean field or full field model will conclude this work. References : [1] Montheillet, F., Lurdos, O., and Damamme, G. (2009). Acta Materialia, 57(5):1602–1612. [2] Bernard, P., Bag, S., Huang, K., and Loge, R. (2011). Science and Engineering: A, 528(24):7357– 7367. [3] Cram, D. G., Zurob, H. S., Brechet, Y. J. M., and Hutchinson, C. R. (2009). Acta Materialia, 57(17):5218–5228. [4] Maire, L., Moussa, C., Bozzolo, N., Scholtes, B., Pino Munoz, D., Bernacki, M. (2016). Journal of Materials Science, 51(24):10970-10981.[5] Scholtes, B., Shakoor, M., Settefrati, A., Bouchard, P.-O., Bozzolo, N., and Bernacki, M. (2015). Computational Materials Science, 109:388–398. [6] Hallberg, H. (2011). Metals, 1(1):16–48. [7] Mellbin, Y., Hallberg, H., and Ristinmaa, M. (2015). Modelling and Simulation in Materials Science and Engineering, 23(4):045011. [8] Sitko, M., Pietrzyk, M., and Madej, L. (2016). Journal of Computational Science, 16:98–113. [9] Zhao, P., Song En Low, T., Wang, Y., and Niezgoda, S. R. (2016). International Journal of Plasticity, 80:38–55.

https://hal-mines-paristech.archives-ouvertes.fr/hal-01504490/document

Modeling of dynamic recrystallization in austenitic stainless steel 304L by coupling a full field approach in a finite element framework with mean field laws

A simplified intragranular description of dislocation density heterogeneities to improve dynamically recrystallized grain size predictions

Many applications involving Fluid-Structure Interaction (FSI) feature large displacements of the boundaries of the computational domain. Despite recent progress in this field, Finite-Element and Finite-Volume simulations of such problems are still challenging. On one hand, interface-capturing techniques such as the level-set or the phase-fields methods can deal with large boundary deformations, but they often fail to correctly take into account the jump in mechanical properties of materials at the interface, and they can only approximate important geometrical singularities such as corners and edges. On the other hand, standard mesh deformation techniques coupled with ALE solvers are appropriate for problems of Fluid-Structure Interaction involving small displacements, but their capacity to maintain the validity and the quality of the mesh under large boundary movements is limited. In this work, we develop a robust mesh deformation method aimed at simulations subject to large boundary displacements. At each time step of the simulation, a displacement is applied to the boundary and the mesh is regularized and improved by means of a continuous optimization technique. A local mesh adaptation procedure involving topological operations is triggered in case the mesh quality falls below a user-given threshold after the optimization stage. The main feature of the algorithm is its robustness with respect to boundary displacements of arbitrary amplitude. We demonstrate the performance of our approach on academic mesh movement test cases and apply it to Finite-Element ALE simulations.

A robust deformation method for unstructured meshes subject to large boundary movements

Grain growth is a well-known and complex phenomenon occurring during annealing of all polycrystalline materials. Its numerical modeling is a complex task when anisotropy sources such as grain orientation and grain boundary inclination have to be taken into account. This article presents the application of the front-tracking methodology ToRealMotion introduced in previous works, to the context of anisotropic grain boundary motion at the mesoscopic scale. The new formulation of boundary migration can take into account any source of anisotropy both at grain boundaries as well as at multiple junctions (MJs) (intersection point of three or more grain boundaries). Special attention is given to the decomposition of high-order MJs for which an algorithm is proposed based on local grain boundary energy minimisation. Numerical tests are provided using highly heterogeneous configurations, and comparisons with a recently developed Finite-Element Level-Set (FE-LS) approach are given. Finally, the computational performance of the model will be studied comparing the CPU-times obtained with the same model but in an isotropic context.

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Marc Bernacki

Papers

Generation and homogenization of foamed polymer RVEs: microstructure-mechanical properties relationship

Modeling of dynamic recrystallization in austenitic stainless steel 304L by coupling a full field approach in a finite element framework with mean field laws

A simplified intragranular description of dislocation density heterogeneities to improve dynamically recrystallized grain size predictions

A robust deformation method for unstructured meshes subject to large boundary movements

A 2D front-tracking Lagrangian model for the modeling of anisotropic grain growth