Identification of nonlinear dynamic behavior and failure for riveted joint assemblies

Many different types of rivets need to be modeled to analyze the crashworthiness of aircraft structures. A numerical procedure based on FE modeling and characterization of material failure constitutive models is proposed herein with the aim of limiting the costs of experimental procedures otherwise necessary to obtain these data. Quasi-static and dynamic experiments were carried out on elementary tension (punched) and shear (riveted) specimens. No strain rate sensitivity was detected in the failure behavior of the riveted joint assemblies. Experimental data were used to identify the Gurson damage parameters of each material (2024-T351 and 7050 aluminum alloys for the sheet metal plate and the rivet respectively) by an inverse method. Characterization gave rise to satisfactory correlation between FE models and experiments. Optimized parameters were validated for each material by means of a uniaxial tension test for the sheet metal plate and an ARCAN type specimen in pure tension for the rivet

Comportement au crash et à l'impact : de l'échelle de la structure à celle des matériaux constitutifs et de leurs assemblages

International audienceLa présentation fera une synthèse des travaux menés dans le contexte du crash et de l'impact par le LAMIH de l’Université de Valenciennes et le Département DADS de l’Onéra depuis une quinzaine d’années. L’accent sera particulièrement porté sur la caractérisation du comportement dynamique de différentes classes de matériaux (incluant le biologique osseux) et sur la tenue mécanique des assemblages soudés et rivetés, à différentes échelles et pour différents trajets de sollicitations

Characterisation and Parameters Identification of Materials Constitutive and Damage Models: From Normalised Direct Approach to Most Advanced Inverse Problem Resolution.

International audienceThe paper aims at providing an overview of the research activities performed from the two past decades at the authors laboratory, in the field of the materials characterisation under dynamic loadings (i.e. from 10^-3 s^-1 to 10^+3 s^-1 for structural crashworthiness and impact applications) and the parameters identification to model their constitutive behaviour and damage. The different testing devices to load the material sample on the expected strain rate range are presented and discussed first, including the different experimental measurement techniques applied to analyse the stress - strain curves. From the normalised direct approach, two different numerical approaches, based on inverse problem resolution techniques, are introduced and discussed: the well-know Finite Element Model Updating method and the most advanced one based on the Virtual Fields Method, that enables to take the full advantages of full-field measurement techniques, such the Digital Image Correlation method. Applications for different materials and models, viscoplastic and damage, are given to support these advanced methods, including the dynamic strength of riveted and welded assemblies

Modélisation par élément finis de la compression de matériaux cellulaires

International audienceStructures made of tubes, stacked in square or hexagonal patterns, have been considered here as model cellular materials. Compression tests have shown large deformations, transformations and also many contact points. Two Finite Element codes have been used to investigate the influence of the elements type (quadrangular or triangular, linear or quadratic) and the numerical scheme (implicit or explicit) on the structural numerical responses. A contact algorithm based on the Pinball method has been implemented in the explicit code. A very good agreement has been found between the predictions of both codes. The numerical responses are close for a given meshes order, whatever the elements type. Whereas the linear meshes cannot be considered as converged, the quadratic meshes predict very well the experimental responses of the structures, especially for the square stacking. The overestimation of the numerical response of the hexagonal stacking might be explained because, experimentally, this stacking exhibits a more scattered and irregular behaviour due to defects (missing brazes, tube misalignment) which were not modelled

Essais de caractérisation dynamique des matériaux aux vitesses moyennes de déformation

International audienceL’exposé s’intéresse au moyen le plus conventionnel de caractérisation dynamique des matériaux, à savoir la machine d’essai hydraulique. On pourrait penser que ces essais sont aujourd’hui parfaitement maîtrisés, ce qui est vrai dans le domaine des sollicitations quasi-statiques où ils sont même normalisés. Ce n’est toujours pas le cas dans le domaine des sollicitations moyennes vitesses (avant le domaine d’application des barres de Hopkinson), alors que ces essais s’avèrent indispensables pour plusieurs raisons qui sont mise en évidence dans le papier. L’exposé rappelle dans un premier temps et dans les grandes lignes quelles sont les capacités et les limitations actuelles de ces vérins hydrauliques rapides. Il adresse ensuite, au-delà des limitations des moyens, plusieurs sources de difficultés qui peuvent – si l’on n’y prend pas garde – rendre caduque tout espoir d’atteindre une caractérisation dynamique intrinsèque du comportement des matériaux testés. Sont évoquées plusieurs questions qui semblent majeures, les pièges et les précautions à prendre pour les éviter : définition des éprouvettes de caractérisation, introduction des efforts dynamiques, instrumentation, acquisition et mesure, et enfin traitement et exploitation de ces essais. En conclusion, après que les principaux acquis du laboratoire CRD de l’ONERA/DADS sur ces questions depuis 30 ans aient été rappelés, sont présentées quelques perspectives et voies d’amélioration aujourd’hui explorées pour adresser les nouveaux défis et les enjeux pour le secteur aéronautique dans ce domaine

Cellular materials made of stacked tubes: influence of the manufacturing process on the dynamic behavior of the constitutive material. part I: microstructure

International audienceCellular materials are very promising as lightweight aeronautical frames thanks to their superior specific mechanical properties such as impact resistance. However, because of the processing routes and heat treatments used in the production process, the material within the cell walls may behave differently from the bulk, and therefore the in situ mechanical properties are often unknown. The present work aims at investigating the link that exists between the processing of cellular architectures and the mechanical properties of their constitutive material. The cellular material studied is an Inconel® 600 tube stacking brazed together using a nickel-phosphorus alloy. The experimental works have been conducted in order to analyse the microstructures of Inconel® 600 tube stacking resulting from brazing and annealing heat treatment. In order to discuss the influence of the manufacturing process of tube stackings on the mechanical properties of their constitutive material, it has been proposed to perform uni-axial tensile tests on tubular specimens. Different material configurations (with or without heat treatments, with or without nickel-phosphorus coating) have been thus characterised and compared, involving both tensile tests from quasi-static to dynamic loads and electron back-scattered diffraction analyses (EBSD) performed on post-mortem specimens

Armoured vehicles subject to mine explosions – an analysis method for operationability and survivability

The paper deals with numerical methodologies to improve the operationability and survivability of armoured vehicle subject to mine explosions. Methods are proposed to model and extract the time history of the impulsive load from a mine explosion, and to restore equivalent loading conditions to a structural analysis calculation. The problem of computing the shock transmitted to the floor through the undercarriage in the case of the explosion of a mine under a wheel is finally investigated. That kind of model enables to discriminate whether the highly dynamic shock is transmitted through the wheel/undercarriage, or directly through the floor