Angers – 4 rue Saint-Maurille

Le projet de construction d’un immeuble situé à 30 m de l’ancienne église Saint-Maurille a nécessité une évaluation archéologique. L’église a été détruite en 1791 et la rue Saint-Maurille percée sur l’emprise du cimetière. Les sondages ont été effectués à l’intérieur d’un garage qui occupe l’emplacement du futur immeuble. Des limites parcellaires qui se sont perpétuées depuis le bas Moyen Âge, jusqu’à la date de construction du garage en 1935 ont été mises au jour, ainsi qu’un tronçon de la c..

Magny-en-Vexin – Collège Claude-Monet

Le conseil Général du Val d’Oise a projeté la rénovation du collège qui est très exactement situé sur l’emprise d’une nécropole mérovingienne. La restructuration comprend divers travaux qui couvrent une surface de 1 700 m dans l’enceinte du collège et à l’extérieur un réaménagement de la gare routière et l’établissement d’une allée piétonne entre cette gare et l’entrée du collège.La nécropole de Magny est connue depuis le xixe s. Des découvertes fortuites de sarcophages ont eu lieu aux alent..

Geometrically Nonlinear Field Fracture Mechanics and Crack Nucleation, Application to Strain Localization Fields in Al-Cu-Li Aerospace Alloys

International audienceThe displacement discontinuity arising between crack surfaces is assigned to smooth densities of crystal defects referred to as disconnections, through the incompatibility of the distortion tensor. In a dual way, the disconnections are defined as line defects terminating surfaces where the displacement encounters a discontinuity. A conservation statement for the crack opening displacement provides a framework for disconnection dynamics in the form of transport laws. A similar methodology applied to the discontinuity of the plastic displacement due to dislocations results in the concurrent involvement of dislocation densities in the analysis. Non-linearity of the geometrical setting is assumed for defining the elastic distortion incompatibility in the presence of both dislocations and disconnections, as well as for their transport. Crack nucleation in the presence of thermally-activated fluctuations of the atomic order is shown to derive from this nonlinearity in elastic brittle materials, without any algorithmic rule or ad hoc material parameter. Digital image correlation techniques applied to the analysis of tensile tests on ductile Al-Cu-Li samples further demonstrate the ability of the disconnection density concept to capture crack nucleation and relate strain localization bands to consistent disconnection fields and to the eventual occurrence of complex and combined crack modes in these alloys

Crystal plasticity modeling of the effects of crystal orientation and grain-to-grain interactions on DSA-induced strain localization in Al–Li alloys

International audienceWe develop a crystal plasticity model to investigate the coupled actions of crystal orientation, grain neighborhood and grain-to-grain elasto-plastic interactions on dynamic strain aging (DSA) and the onset and development of associated plastic strain localization in Al-Li alloys. Considering simple model multilayered microstructures with preferred orientations representative of rolled alloys, the aim is to identify grain orientation couples that can limit dynamic strain aging induced strain localization without compromising the flow stress and strain hardening properties. To this end, a slip system-based formulation of dynamic strain aging is implemented in a crystal plasticity finite element framework. The model validity is first checked with the simulation of a tensile specimen loaded at quasi-static applied strain rate. The introduction of dynamic strain aging allows predicting complex propagation of intense plastic localization bands. We further investigate the influence of crystal orientations on early strain localization in Al-Cu-Li-Mg alloys, by performing simulations representative of the early stage of a Kahn Tear test for single crystals and layered polycrystals. Using experimentally reported crystal orientations for rolled microstructures, the simulation results show that in both single and multilayered crystals, there is a strong influence of dynamic strain aging on localization patterns, as well as a significant orientation dependence. In multilayered crystals, the nature of strain localization can be remarkably modified when stand-alone crystals of a certain orientation are coupled with other orientations: strain localization may intensify or fade away depending on the coupling with neighboring orientations

A Fast Fourier Transform-based approach for Generalized Disclination Mechanics within a Couple Stress theory

International audienceRecently, a small-distortion theory of coupled plasticity and phase transformation accounting for the kinematics and thermodynamics of generalized defects called generalized disclinations (abbreviated g- disclinations) has been proposed. Then, a first numerical spectral approach has been developed to solve the elasto-static equations of field dislocation and g-disclination mechanics set out in this theory for periodic media and for linear elastic media using the classic Hooke’s law. Here, given a spatial distribution of generalized disclination density tensors in a homogenous linear higher order elastic media described, a couple stress theory with elastic incompatibilities of first and second orders is developed. The incompatible and compatible elastic second and first distortions are obtained from the solution of Poisson and Navier-type equations in the Fourier space. The efficient Fast Fourier Transform (FFT) algorithm is used based on intrinsic Discrete Fourier Transforms (DFT) that are well adapted to the discrete grid to compute higher order partial derivatives in the Fourier space. Therefore, stress and couple stress fields can be calculated using the inverse FFT. The numerical examples are given for straight wedge disclinations and associated wedge disclination dipoles which are of importance to geometrically describe tilt grain boundaries at fine scales in polycrystalline solids

Continuous description of the atomic structure of grain boundaries using dislocation and generalized-disclination density fields

AbstractAn atomistic-to-continuum method is developed to derive dislocation, generalized-disclination density fields and the associated elastic strain, rotation, curvature and second-distortion fields from the atomic structure of grain boundaries. From the relaxed and un-relaxed atomic positions, calculation of the transformation gradient feeds a mechanical framework, where discontinuities of the lattice elastic displacement and distortion (rotation and strain) are captured by smooth incompatible strain and second-distortion fields associated with the dislocation and generalized-disclination density fields, respectively. The method is applied to a copper symmetrical tilt boundary as obtained from molecular dynamics simulations. The core structure of the boundary is found to contain edge dislocations and dipoles of generalized-disclinations, including standard wedge-disclination dipoles. The latter reflect in particular localized shear and stretch discontinuities across the interface, in addition to the overall rotation discontinuity

Magny-en-Vexin – Collège Claude-Monnet

Le site est connu pour être implanté sur une nécropole mérovingienne (fouilles de 1972). Les travaux de rénovation du collège ont donc déclenché cette opération qui s’est déroulée en décembre 1997 et janvier 1998. Les résultats de l’opération ont été présentés dans le BSR 1997 (p. 155-156). Il restait cependant à évaluer le secteur VIII (aménagement d’un patio dans la cour, au droit du bâtiment A). Cinq sondages ont été ouverts en juin 1998. Ils se sont tous révélés stériles. Ce résultat conf..

Vers une approche à champs moyens à longueurs internes validée par dynamique des champs de dislocations : application aux effets de taille de particules dures dans un matériau de type ferrite / carbures

Une approche à champs moyens à longueurs internes rend compte des effets de taille d’inclusions dures noyées dans une matrice ferritique. Une couche intermédiaire entre l’inclusion et la matrice reflète la présence de GND dues aux gradients de distorsion plastique. L’épaisseur de cette couche et ses effets sur l’écrouissage sont obtenus à l’aide d’une théorie mécanique des champs de dislocations basée sur l’incompatibilité de réseau et l’équation de transport des dislocations de Mura

MERIT, a cellular system coordinating lysosomal repair, removal and replacement

Membrane integrity is essential for cellular survival and function. The spectrum of mechanisms protecting cellular and intracellular membranes is not fully known. Our recent work has uncovered a cellular system termed MERIT for lysosomal membrane repair, removal and replacement. Specifically, lysosomal membrane damage induces, in succession, ESCRT-dependent membrane repair, macroautophagy/autophagy-dominant removal of damaged lysosomes, and initiation of lysosomal biogenesis via transcriptional programs. The MERIT system is governed by galectins, a family of cytosolically synthesized lectins recognizing β-galactoside glycans. We found in this study that LGALS3 (galectin 3) detects membrane damage by detecting exposed lumenal glycosyl groups, recruits and organizes ESCRT components PDCD6IP/ALIX, CHMP4A, and CHMPB at damaged sites on the lysosomes, and facilitates ESCRT-driven repair of lysosomal membrane. At later stages, LGALS3 cooperates with TRIM16, an autophagy receptor-regulator, to engage autophagy machinery in removal of excessively damaged lysosomes. In the absence of LGALS3, repair and autophagy are less efficient, whereas TFEB nuclear translocation increases to compensate lysosomal deficiency via de novo lysosomal biogenesis. The MERIT system protects endomembrane integrity against a broad spectrum of agents damaging the endolysosomal network including lysosomotropic drugs, Mycobacterium tuberculosis, or neurotoxic MAPT/tau. Abbreviations: AMPK: AMP-activated protein kinase; APEX2: engineered ascorbate peroxidase 2; ATG13: autophagy related 13; ATG16L1: autophagy related 16 like 1; BMMs: bone marrow-derived macrophages; ESCRT: endosomal sorting complexes required for transport; GPN: glycyl-L-phenylalanine 2-naphthylamide; LLOMe: L-leucyl-L-leucine methyl ester; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MERIT: membrane repair, removal and replacement; MTOR: mechanistic target of rapamycin kinase; TFEB: transcription factor EB; TFRC: transferrin receptor; TRIM16: tripartite motif-containing 16

Galectin-3 Coordinates a Cellular System for Lysosomal Repair and Removal

Jia et al. show that Galectin-3 recruits ESCRT components to damaged lysosomes for repair and restoration of their function. During sustained lysosomal injury, galectins induce autophagy and lysosomal biogenesis for a staged repair, removal, and replacement program. This response is deployed during damage with neurotoxic tau or Mycobacterium tuberculosis infection