Optimal component mode synthesis for medium frequency problem

International audienceThe component mode synthesis (CMS) with fixed interface (denoted Craig–Bampton) method uses a combination of static and dynamic modes. The usual definition of this CMS leads to a coupling between static and dynamic modes which are not orthogonal with respect to the stiffness matrix. This type of basis is not well suited for dynamic explicit computations, because the resulting mass matrix is not diagonal. If one keeps the same basis mode set but uses an orthogonalization process with respect to the mass matrix, the quality of the reduced Craig–Bampton system is kept but the basis vectors are combined differently. The aim of this paper is to propose a new way to control the accuracy of the reduced dynamic system for a specific frequency domain. Thus a new CMS is defined in order to be accurate in the medium frequency range

Influence de la loi de comportement sur la prévision de l'éclatement d'un disque de turbomachine

National audienceLes matériaux élastomères chargés en Noir de Carbone constituant la gomme des matériaux pneumatiques sont habituellement considérés comme homogènes à l'échelle de la structure. À une échelle plus fine, de l'ordre du micromètre ils présentent une structure hétérogène. Cette microstructure biphasée (matrice + inclusions) caractérise le mélange polymère-Noir de Carbone (NC). Les propriétés mécaniques macroscopiques du matériau élastomère chargé dépendent très fortement de ses caractéristiques microstructurales. On cherche à établir le lien existant entre les deux échelles d'étude (structure et microstructure). On identifie la microstructure par la morphologie des charges de Noir de Carbone dans la matrice polymère et par les propriétés mécaniques de chacun des constituants. On modélise ici la morphologie du matériau d'étude à l'échelle microscopique pour laquelle les deux phases sont mises en jeu (matrice polymère + NC). La modélisation choisie s'appuie sur des outils de la morphologie mathématique et a largement été étudiée dans de nombreux travaux. L'observation et la caractérisation de la microstructure à modéliser s'effectue à l'aide d'outils tels que la microscopie à transmission ou encore l'analyse d'images

High strain rate behavior of MC2 single crystal under uniaxial compression load at high temperature: Experiments and modeling

International audienceThis paper presents experimental and numerical investigations on single crystal nickel base superalloy MC2. The purpose of this study is to efficiently predict the consequences of impacts on turbine blades within gas turbine engines. Dynamic compression tests on Split Hopkinson Pressure Bar (SHPB), performed at high temperature, have allowed the identification of anisotropic and viscoplastic material data. The effects of crystal orientation (〈1 0 0〉, 〈1 1 0〉 and 〈1 1 1〉), temperature (25, 750 and 1000 °C) and strain rate (up to 610 s) on the compression yield strength and work hardening of MC2 single crystal have been examined. The LS-Dyna solver has been used to calibrate the parameters of a phenomenological behavior law based on a local Hill yield criterion. The results of simulations have been verified by comparison with a ballistic test on a monocrystalline plate, and on a turbine blade heated at 1000 °C. The measured residual deflections and strain fields are consistent with those obtained by calculation

Simulation de l'effet Portevin-Le Chatelier dans un superalliage pour disque de turbomachine

International audienceA model proposed by (MacCormick, 1989) describing dynamic strain aging is used for a turbine disc superalloy. An analytic solution is calculated for simple tension, and a linear perturbation analysis is performed to evaluate the critical strain. The convergence toward this critical value of two numerical integration schemes of material law is studied. A stability analysis based on (Hill, 1958) criteria is made from the simulation of a tensile test on a plate.Un modèle de comportement proposé par (MacCormick, 1989) décrivant le vieillissement dynamique des matériaux est utilisé pour modéliser un superalliage pour disques de turbomachine. Le modèle est présenté en petites déformations, une solution analytique homo-gène en traction simple est calculée, puis la déformation critique d'instabilité est déterminée à l'aide d'une analyse de perturbation linéaire. Cette valeur critique permet d'évaluer la convergence de deux schémas numériques d'intégration de la loi de comportement. Une analyse de stabilité basée sur les critères de (Hill, 1958) est réalisée sur une simulation par éléments finis d'une plaque en traction

Overspeed burst of elastoviscoplastic rotating disks – Part I: Analytical and numerical stability analyses

International audienceBurst of rotating disks in case of overspeed is investigated. The certification of turbo-engines requires to demonstrate the integrity of disks at higher rotation speeds than the maximum rotation speed reachable in service. The determination of the burst speed by analysis can help to reduce the number of tests required for the certification. This prediction can be established by non-linear stability analyses of finite element simulations. Non-linearities originate from (i) the material behaviour described by elastoviscoplastic constitutive equations, (ii) geometric changes accounted for by the finite strain formulation. In this work, loss of uniqueness and loss of stability criteria from [Hill, R., 1958. A general theory of uniqueness and stability in elastic-plastic solids. J. Mech. Phys. Solids 6, 236–249] are applied. The loss of stability criterion is restricted to the case of rotating disks and compared to several simple widely used material based failure criteria. 3D simulations of rotating metal disks are performed for a given elastoviscoplastic behaviour and the stability criteria are evaluated. The sensitivity of disk stability to material parameters, such as yield criterion, hardening and viscosity is evaluated in the case of a nickel based superalloy

Numerical aspects in the finite element simulation of the Portevin–Le Chatelier effect

International audienceSerrated yielding and propagation of localized bands of plastic strain rate are the apparent phenomena of the Portevin–Le Chatelier (PLC) effect. The finite element modeling of this effect is investigated, using a model proposed by Zhang et al. [74] describing dynamic strain aging, and material parameters for a Nickel based superalloy at 500 °C. This work presents: (1) an efficient implicit integration scheme of the constitutive equations in the presence of instabilities; (2) a numerical tool to determine the type of plastic strain rate localization bands based on results of simulations; and (3) a mesh and time discretization sensitivity analysis of the model regarding the characteristics of PLC bands. This analysis is carried out in 2D and 3D for axisymmetric smooth and notched specimens

Overspeed burst of elastoviscoplastic rotating disks : part II : Burst of a superalloy turbine disk

International audienceBurst of a turbo-engine disk in case of overspeed is investigated both from experimental and computational point of view. Two twin disks made of the same nickel based superalloy are tested. For the first one (B-disk), rotation rate in increased till burst. The second one (S-disk) is kept safe by stopping rotation just before burst, and unloading it to measure residual deformations. The material model parameters are deduced either from simple tension tests, or using an inverse method on the S-disk test. Two corresponding finite element simulations of the B-disk are then performed, using either an arc-length control method to overcome the limit point, or dynamic simulations. In both cases, the numerical burst rotation rate, associated with the loss of stability of the structure, is found to be in good agreement with the experimental result

Type I interferon signaling protects mice from lethal henipavirus infection.

International audienceHendra virus (HeV) and Nipah virus (NiV) are closely related, recently emerged paramyxoviruses that form Henipavirus genus and are capable of causing considerable morbidity and mortality in a number of mammalian species, including humans. However, in contrast to many other species and despite expression of functional virus entry receptors, mice are resistant to henipavirus infection. We report here the susceptibility of mice deleted for the type I interferon receptor (IFNAR-KO) to both HeV and NiV. Intraperitoneally infected mice developed fatal encephalitis, with pathology and immunohistochemical features similar to what was found in humans. Viral RNA was found in the majority of analyzed organs, and sublethally infected animals developed virus-specific neutralizing antibodies. Altogether, these results reveal IFNAR-KO mice as a new small animal model to study HeV and NiV pathogenesis, prophylaxis, and treatment and suggest the critical role of type I interferon signaling in the control of henipavirus infection