Modélisation et simulation numérique par méthode FFT de la localisation des contraintes internes et des densités de dislocations dans un acier composite nouvelle génération 'Fe-TiB2'

International audienceUn modèle d'élasto-viscoplasticité cristalline (EVP), basé sur la méthode des transformées de Fourier rapide (FFT) et couplé à la mécanique des champs de dislocations (MFDM), est présenté et appliqué afin de décrire l'évolution en déformation des densités de Dislocations Géométriques Nécessaires (GND) dans un composite à matrice métallique Fe-TiB2. Des volumes élémentaires réalistes basés sur la microstructure réelle sont considérés. Les résultats montrent la capacité de l'approche à prédire les gradients des champs mécaniques proches des interfaces matrice/renforts

Single high-dose erythropoietin administration immediately after reperfusion in patients with ST-segment elevation myocardial infarction: results of the Erythropoietin in Myocardial Infarction Trial

Background Preclinical studies and pilot clinical trials have shown that high-dose erythropoietin (EPO) reduces infarct size in acute myocardial infarction. We investigated whether a single high-dose of EPO administered immediately after reperfusion in patients with ST-segment elevation myocardial infarction (STEMI) would limit infarct size. Methods A total of 110 patients undergoing successful primary coronary intervention for a first STEMI was randomized to receive standard care either alone (n = 57) or combined with intravenous administration of 1,000 U/kg of epoetin β immediately after reperfusion (n = 53). The primary end point was infarct size assessed by gadolinium-enhanced cardiac magnetic resonance after 3 months. Secondary end points included left ventricular (LV) volume and function at 5-day and 3-month follow-up, incidence of microvascular obstruction (MVO), and safety. Results Erythropoietin significantly decreased the incidence of MVO (43.4% vs 65.3% in the control group, P = .03) and reduced LV volume, mass, and function impairment at 5-day follow-up (all P < .05). After 3 months, median infarct size (interquartile range) was 17.5 g (7.6-26.1 g) in the EPO group and 16.0 g (9.4-28.2 g) in the control group (P = .64); LV mass, volume, and function were not significantly different between the 2 groups. The same number of major adverse cardiac events occurred in both groups. Conclusions Single high-dose EPO administered immediately after successful reperfusion in patients with STEMI did not reduce infarct size at 3-month follow-up. However, this regimen decreased the incidence of MVO and was associated with transient favorable effects on LV volume and function

Micro-Strain and Cyclic Slip Accumulation in a Polycrystalline Nickel-Based Superalloy

International audienceThis work provides a comprehensive characterization and analysis of deformation and fatigue damage mechanisms in a nickel-based superalloy during ambient temperature fatigue and points to a fundamental deformation mechanism that results in the onset of crack nucleation. Strain and slip irreversibility are investigated at the nanometer scale using high-resolution digital image correlation and high-resolution electron backscatter diffraction, highlighting distinct deformation mechanisms contributing to crack nucleation. It is observed during early fatigue cycling at relatively low applied stress, the formation of intense slip events that induce grain boundary shearing. This results in intense micro-scale strain in the neighboring grains, producing localized plasticity and stresses. Such stresses facilitate fatigue extrusion-intrusion mechanisms during subsequent cycling, resulting in preferred crack nucleation. Finally, the configurations within the microstructure that promote such deformation and damage mechanisms sequence are highlighted

Strain localization in Ti and Ti-alloys using three-dimensional topographic imaging

International audienceUnderstanding strain localization in titanium and titanium alloys is central to depicting better how individual grains plastically deform and how grain orientation distribution, i.e., the local texture, affects the strain distribution within large regions of interest. High-resolution imaging over large fields of view is vital in detecting the nanometer-scale elementary and irreversible deformation mechanisms as a function of the variability of mesoscopic deformation inherited from the former millimeter-scale β-grains. High Resolution-Digital Image Correlation (HR-DIC) is used to assess quantitative deformation fields from the macroscopic to the microscopic scales. Moreover, HR-DIC is used to identify slip activity in the various polycrystalline Ti and Ti-alloys. Identification of slip systems was obtained using imaging from both scanning electron microscope (SEM) and laser scanning confocal microscope (LSCM). SEM provides a high spatial resolution in the surface plane, while LSCM micrographs provide out-of-plane measurements. Both imaging techniques are complementarily used to identify deformation slip and sliding at the sub-grain scale. In-situ HR-DIC under SEM paired with ex-situ LSCM and conventional SEM observations were used to identify three-dimensional surface strain localization and subsequently slip activity in the various Ti and Ti-alloys under tensile loading at room temperature. Interrupted tensile tests were performed to inform sliding evolution as a function of the applied plastic strain. Both in-plane and out-of-plane sliding displacement were evidenced at the sub-grain level leading to an increase in roughness with increasing applied plastic strain. Interestingly, former β-grains strongly affect both strain distribution and slip activity