Characterization and modeling of ductile rupture with relationship to microstructures in 2198 Al-Li alloy for aeronautic application

International audienceDamage and fracture mechanisms of two 2198 Al-Li thin sheet alloys having different thicknesses (2 and 6 mm) are investigated. Two heat treatments are studied: T3 and T8. Mechanical tests are carried out on flat specimens including smooth tensile samples and U-notched specimens (with various notch radii). Test data are used to identify the parameters of constitutive equations describing plastic anisotropy. Crack initiation and stable propagation is studied using Kahn tear tests. The microscopic fracture surface of the different specimens is observed using SEM (Scanning Electron Microscopy). Smooth and notched samples exhibit a slant fracture surface. With increasing notch severity, the fracture mode changes significantly. Failure initiates at the notch root in a small triangular region, outside this zone, slant fracture is observed. Observations show two different failure mechanisms with respect to triangular and slant zones

A combined phenomenological model for the representation of anisotropic hardening behavior in high strength steel line pipes

International audienceLine pipes have anisotropic mechanical properties, such as tensile strength, ductility and toughness. These properties depend on both prestrain during the cold forming process and on the anisotropy of the mother plates. In this study, a phenomenological model combining isotropic and kinematic hardening is developed to represent anisotropic hardening behavior of high strength steel line pipes. The model is adjusted on experiments carried out on smooth and notched axisymmetric bars and plane strain specimens. The model is used to simulate bending tests carried out on large pipes containing a geometric imperfection.Numerical results suggest that prestraining in pipe forming process significantly affects the bending capacity of pipes

Use of the sent specimen in pipeline design

International audienceEngineering critical assessments have been developed based on fracture mechanics principles to determine whether or not a given flaw is safe from failure under specified loading conditions. Several parameters are required as inputs, such as the geometry of the flaw, the stress acting at the vicinity of the flaw and the material properties (toughness, tensile properties). To do so, advanced fracture-mechanics testing (critical K, CTOD or J) are usually required to guarantee an accurate measurement of the material toughness. It is accepted that the Compact Tension (CT) and the Single-Edge Notched Bending (SENB) may lead to unnecessary conservatism in safety assessments. The Single-Edge Notched Tensile (SENT) specimen could be the most acceptable substitute since it is shown to lead to less conservatism

Ductile rupture of prestrained X100 pipeline steel sheets

International audienceThe mechanical and damage behavior of a X100 steel after prestrain is studied in thiswork. Experimental results show both a plastic and rupture anisotropy: the T direction exhibits ahigher ultimate stress but the lowest ductility and toughness. Prestrain reduces ductility and crackgrowth resistance. A model able to represent the plastic and damage behaviour of the material beforeand after prestrain is proposed. The model incorporates plastic anisotropy, kinematic hardening, voidgrowth of the primary cavities, nucleation of secondary voids on carbides. Using the model afterimplementation in a FE software, allows to reproduce experimental trends

ductile fracture assessment of x65 steel using damage mechanics

Abstract: Strain-based design for offshore pipeline requires a considerable experimental work aimed to determine the material fracture toughness and the effective strain capacity of pipe and welds. Continuum damage mechanics can be used to limit the experimental effort and to perform most of the assessment analysis and evaluation at simulation level. In this work, the possibility to predict accurately ductile rupture in X65 class steel for offshore application, using a CDM model, is shown. The procedure for material and damage model parameters identification is presented and applied to X65, customer grade steel. Then, damage model predictive capabilities have been validated predicting ductile crack growth in SENB and SENT fracture specimen

Three-dimensional crack propagation behavior in hydrogen-related fracture of high-strength martensitic steel

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Mécanismes locaux de déformation de l'acier inoxydable austénitique 316L

International audienceDans cette étude, nous présentons une approche nouvelle pour comprendre les mécanismes locaux de déformation.Les champs cinématiques obtenus à partir d’une grille nanoparticules d’orsont combinés aux mesures cristallographiques de la région de la grille. Les déformations dans les grains et aux joints de grains et l’apparition des glissements et leurs évolutions sont suivies. Ces résultats locaux sont comparés au comportement macroscopique fourni lors d’un essai de traction

Plasmonic mode interferences and Fano resonances in Metal-Insulator-Metal nanostructured interface OPEN

International audienceMetal-insulator-metal systems exhibit a rich underlying physics leading to a high degree of tunability of their spectral properties. We performed a systematic study on a metal-insulator-nanostructured metal system with a thin 6 nm dielectric spacer and showed how the nanoparticle sizes and excitation conditions lead to the tunability and coupling/decoupling of localized and delocalized plasmonic modes. We also experimentally evidenced a tunable Fano resonance in a broad spectral window 600 to 800 nm resulting from the interference of gap modes with white light broad band transmitted waves at the interface playing the role of the continuum. By varying the incident illumination angle shifts in the resonances give the possibility to couple or decouple the localized and delocalized modes and to induce a strong change of the asymmetric Fano profile. All these results were confirmed with a crossed comparison between experimental and theoretical measurements, confirming the nature of different modes. The high degree of control and tunability of this plasmonically rich system paves the way for designing and engineering of similar systems with numerous applications. In particular, sensing measurements were performed and a figure of merit of 3.8 was recorded ranking this sensor among the highest sensitive in this wavelength range. Surface plasmon polariton (SPP) and Localized surface plasmon (LSP) have attracted numerous researchers due to their high technological potential. SPP's are surface waves confined near a metal dielectric interface that can propagate over large distances 1 , making them appealing for applications in biosens-ing 2,3. On the other hand LSP resonances can be defined as the localized resonance condition that massively enhances the electromagnetic field in the vicinity of a metal nanoparticle (NP), when the NP have dimensions much smaller than the excitation wavelength 4. LSP resonance is very sensitive to changes in the NP's dimensions, the dielectric constant of the surrounding media and the nature of the substrate. Because of intense local electrical field enhancements and sharp resonance excitation peaks, metallic NPs are of great interest for applications in surface enhanced Raman spectroscopy (SERS) 5 , chemical and biological sensors 3,6 , cancer treatment 7 and light harvesting 8–10. Recently, strong attention was paid to the potentials of SPP and LSP combinations by investigating metallic NPs on top of metallic thin films. Several studies on such systems have indeed shown the coupling and hybridization between localized and delocalized modes, and the effect of the thickness of the dielectric spacer. Those works have revealed that such coupled systems exhibit enhanced optical properties and larger tunability of their spectral properties compared to uncoupled systems 1,4,11–2

Endommagement et rupture des aciers : de la mini-éprouvette à la structure

The research focuses on the damage and failure of metallic materials. The manuscript begins with some reflections on the experimental study of damage and fracture of materials or structures, with a focus on tools and methods (data processing, instrumentation for laboratory or structural tests, deformation measurements at different scales, prototype for crack monitoring, 3D characterization of damage by X-ray micro-tomography, ...). The second chapter is dedicated to the characterization and modeling, within the framework of the local approach, of plastic and ductile fracture anisotropy of metals. The third chapter is devoted to the influence of pre-deformation on the toughness and fatigue strength of steels for gas or oil transport. Finally, two perspectives focusing on energy transition and preparation for hydrogen transport are presented: (i) the development of subsize specimen for in-service monitoring of industrial structures, and (ii) the development of cold spray protection of steel networks.Les travaux de recherche portent sur l’endommagement et la rupture des matériaux métalliques. Le manuscrit commence par quelques réflexions sur l’étude expérimentale de l’endommagement et la rupture des matériaux ou des structures, avec une focalisation sur les outils et méthodes (traitement de données, instrumentation d’essais de laboratoire ou sur structure, mesures de déformations à différentes échelles, prototype de suivi de fissures, de caractérisation 3D de l’endommagement par micro-tomographie X, ...). Le second chapitre est dédié à la caractérisation et la modélisation, dans le cadre de l’approche locale, d’une anisotropie, plastique et de rupture ductile, des métaux. Le troisième chapitre est consacré à l’influence de la prédéformation sur la ténacité et la résistance à la fatigue d’aciers de transports de gaz ou de pétrole. Enfin, deux perspectives axées sur la transition énergétique et la préparation au transport d’hydrogène sont présentées : (i) le développement des mini-éprouvettes pour le suivi en service des structures industrielles, et (ii) le développement d’une protection par cold spray des réseaux en aciers

COMPORTEMENT ET DUREE DE VIE D'UNE JONCTION TUBULAIRE SOUDEE EN 316L A 600\C

CLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF