Unified model for Mullins effect and high cycle fatigue life prediction of rubber materials

Proceedings of the 8th European Conference on constitutive models for rubbers (ECCMR VIII), San Sebastian, Spain, 25-28 June 2013International audienceThe study describes the basic principles of a general damage model (GDMF) for Mullins effect and high cycle fatigue loadings of rubber materials and demonstrates its prediction possibilities for simulating the complete fatigue failure phenomenon. The present paper focuses on stiffness modelling of rubber materials for uniaxial and multiaxial static and fatigue loadings with a minimal number of material parameters in order to ensure robustness of the identification. The proposed hyperplastic model is expressed in terms of classical independent strain invariants. Mullins effect and high cycle fatigue loadings are both modelled according to a continuum damage mechanics approach

Capilano College Fall 1986 Reading Series

Poster with dates and times of the Fall 1986 Reading Series, featuring Sharon Pollock, Sandra Birdsell, and Fred Wah

A theory of network alteration for the Mullins effect

International audienceThis paper reports on the development of a new network alteration theory to describe the Mullins effect. The stress-softening phenomenon that occurs in rubber-like materials during cyclic loading is analysed from a physical point of view. The Mullins effect is considered to be a consequence of the breakage of links inside the material. Both filler-matrix and chain interaction links are involved in the phenomenon. This new alteration theory is implemented by modifying the eight-chains constitutive equation of Arruda and Boyce (J. Mech. Phys. Solids 41 (2) (1993) 389). In the present method the parameters of the eight-chains model, denoted C-R and N in the bibliography, become functions of the maximum chain stretch ratio. The accuracy of the resulting constitutive equation is demonstrated on cyclic uniaxial experiments for both natural rubbers and synthetic elastomers

A new modelling of the Mullins'effect and viscoelasticity of elastomers based on physical approach

The mechanical behaviour of elastomers is known to be highly non-linear, time-dependent and to exhibit hysteresis and stress-softening known as the Mullins effect (Mullins, 1948) upon cyclic loading. These phenomena are classically studied and modelled independently. Some studies are based on physical approaches (Arruda and Boyce, 1993; Bergström and Boyce, 1998; Marckmann et al., 2002) in which macroscopic constitutive equations are build in regards with the physics of polymeric chains. In this context of physical considerations, the aim of the present paper is to study independently each phenomenon involved in rubber-like materials and to assemble them in a global constitutive equation. First, the hyperelastic behaviour of elastomers is modelled by the physical approach of Arruda and Boyce (1993), widely known as the eight-chains model. This model accurately reproduces the large strains elastic behaviour of elastomers under different types of deformation. Second, the hysteretic time dependent behaviour is approached by the model developed by Bergström and Boyce (1998) that considers the separation of the network in two phases: an elastic equilibrium network and a viscoelastic network that captures the nonlinear rate-dependent deviation from equilibrium. This model is quite simple and successfully reproduces the rate-dependent hysteretic properties of elastomers. Last, as shown in the bibliography, the Mullins stress-softening effect can be considered as a damage phenomenon which only depends on the maximum stretch attained during the deformation history (Govindgee and Simo, 1992). In the present approach, the physical theory of Marckmann et al. (2002) based on an alteration of the polymeric network is adopted. This theory was introduced in the eight-chains hyperelastic model and successfully simulates the decrease of the material stiffness between the first and the second loading curves under cyclic loading. As these three models are based on the physics of the polymeric network, they are gathered in a new efficient constitutive equation. This model is able to reproduces imultaneously the Mullins effect and the time-dependent hysteretic behaviour of elastomers. Finally, the constitutive parameters of this new model are identified by fitting experimental data

Theoretical and numerical limitations for the simulation of crack propagation in natural rubber components

International audienceIn this paper, two commercial software packages dedicated to the simulation of crack propaga-tion in elastomer components were tested: FLEXPAC and MSC-MARC. Firstly, the theoretical limitations ofclassical crack propagation laws were examined to demonstrate that actual numerical predictions are limitedto very simple loading conditions. Secondly, crack propagation approaches implemented in both softwareswere analysed. In order to compare their performances, fatigue experiments are performed. Different rubbercomponents with different pre-cracks were tested under several loading conditions. Crack propagation, i.e.size and direction of the crack, was measured as a function of the number of cycles. Then, these results werecompared with crack direction criteria proposed by the two models. It was demonstrated that loading ampli-tude highly influenced the crack direction and that the models must take this into account in their solver. Fi-nally, limitations of this type of numerical analysis to predict the duration life of rubber components werehighlighted

Caractérisation des dommages au choc de composites stratifiés aéronautiques : application à la chute d'objets

International audienceCette étude porte sur la caractérisation des dommages de plaques stratifiées carbone/époxy suite à un impact basse vitesse. Les stratifiés étudiés sont constitués de nappes pré-imprégnées unidirectionnelles superposées de M21/T700GC. Les essais ont été réalisés en faisant varier masse de l'impacteur et hauteur de chute en conservant pour chaque essai, un niveau d'énergie identique recommandée par la norme aéronautique. L'instrumentation de l'essai ainsi que l'analyse multi physique réalisée sur les plaques impactées ont permis de mieux comprendre les mécanismes d'endommagements du matériau stratifié testé. En effet, ont été couplés accéléromètre, caméra rapide et jauges de déformations pour les mesures pendant l'essai. Une étude thermographique et une analyse aux ultrasons des plaques impactées ont révélés la localisation des endommagements dans les différents stratifiés testés. A niveau d'énergie initiale constante, les plaques testées avec la masse la plus importante sont très largement endommagées par rapport aux plaques impactées avec une faible masse

Chemotherapy of advanced small-bowel adenocarcinoma: a multicenter AGEO study

Les adénocarcinomes de l’intestin grêle (AIG) sont des tumeurs rares et de mauvais pronostic à un stade avancé. Les données publiées concernant l’efficacité de la chimiothérapie palliative sont peu nombreuses. Le but de notre étude était d’évaluer l’efficacité et la tolérance de différents protocoles « modernes » de chimiothérapie et de comparer l’efficacité des chimiothérapies à base de sels de platine dans le traitement de première ligne des AIG avancés. Cette étude rétrospective multicentrique a inclus 93 patients (sexe masculin : 53 % ; âge médian : 56 ans ; site primitif duodénal : 53 %) avec un AIG avancé (métastatique : 86 %) traités par LV5FU2 (n = 10), FOLFOX (n = 48), FOLFIRI (n = 19) ou LV5FU2- cisplatine (n = 16). Le taux de toxicité grade 3-4 était significativement plus fréquent dans le groupe de patients traités par LV5FU2-cisplatine (75 %) comparativement aux autres groupes de patients (p = 0,001). Les médianes de survie sans progression (SSP) étaient de 7,7 ; 6,9 ; 6,0 et 4,8 mois (p = 0,16) et les médianes de survie globale (SG) étaient de 13,5 ; 17,8 ; 10,6 et 9,3 mois (p = 0,25) pour les quatre groupes de patients traités par LV5FU2, FOLFOX, FOLFIRI et LV5FU2-cisplatine, respectivement. En analyse multivariée, l’indice de performance OMS à 2 (p < 0,0001) ainsi que des taux élevés d’ACE (p = 0,02) et de CA 19-9 (p = 0,03) avant traitement étaient les seuls facteurs indépendants significativement associés à un mauvais pronostic. Dans le sous-groupe de patients traités par sels de platine, ceux qui ont reçu une chimiothérapie par FOLFOX avaient de meilleures SSP et SG que les patients traités par LV5FU2-cisplatine. En analyse multivariée, le traitement par FOLFOX était un facteur significatif et indépendant de survie prolongée en termes de SSP (p < 0,0001) et SG (p = 0,02). Ainsi, cette étude, la plus grande rapportée à ce jour, suggère d’une part que l’indice de performance OMS et les taux d’ACE et CA 19-9 avant traitement sont des facteurs pronostiques indépendants de survie et, d’autre part que la chimiothérapie par FOLFOX est le traitement de choix en première ligne des AIG avancés

Contribution à l'étude des élastomères et au dimensionnement des structures stratifiées « sandwich » à usage nautique

Dans le domaine industriel, les calculs non-linéaires prennent actuellement une part de plus en plus importante dans le processus de conception des structures. La faiblesse de la connaissance du comportement des matériaux élastomères nécessite la mise en place de méthodes expérimentales et de modélisations spécifiques afin d'effectuer des simulations numériques réalistes de la déformation et de l'endommagement des structures antivibratoires sous des chargements de fatigue. Les modèles de comportement développés dans ce travail sont basés en partie sur mon expérience dans le domaine de la mécanique de l'endommagement des matériaux et des structures. Des essais mécaniques de fatigue ainsi que l'étude des mécanismes de ruptures à l'échelle macroscopique et microscopique sont présentés. Les deux axes de mes travaux de recherche sont exposés sous cinq chapitres, les trois premiers ayant trait à la modélisation et à la simulation de l'endommagement des composites et les deux derniers traitant du domaine de la simulation du comportement des matériaux et des structures en élastomère sous chargement de fatigu

Finite element damage prediction of composite structures

International audienceThis study recalls the basic principles of a general damage computational approach for laminates and shows its possibilities for simulating the complete fracture phenomenon in the case of complex structures. For composites, continuum damage mechanics models are recalled. They are constitutive relations which, when included in a structural analysis code, are able to predict the damage state at any time and at any point of the studied structure until final fracture. The predictions are obtained with an extended version of the Finite Element code Castem 2000 (C.E.A.) developed specifically for laminate composite structures. This study describes, for carbon-fiber/epoxy-resin laminated composites, some examples of damage and delamination predictions by means of a damage mechanics computational approach

Failure and effective elastic properties predictions of Nomex (R) honeycomb cores

The purpose of the present study is to determine the components of the effective elasticity tensor and the failure properties of Nomex® honeycomb cores. In order to carry out this study, the NidaCore software, a program dedicated to Nomex® Cores predictions, has been developed using the Finite Element tool Cast3M-CEA. This software is based on periodic homogenization techniques and on the modelling of structural instability phenomena. The homogenization of the periodic microstructure is realized thanks to a strain energy approach. It assumes the mechanical equivalence between the microstructures of a RVE and a similar homogeneous macroscopic volume. The key point of the modelling is that by determining the RVE buckling modes, the ultimate stress values of the homogenized core can be deduced. The numerical analysis shows an adequation between the first critical buckling modes computed and the ultimate stress values experimentally observed in standardized tests. This approach, strengthened by experimental data, makes it possible to devise a failure criterion. This criterion relies on the understanding of the mechanical effects caused by a local damage. In order to improve the reliability of the software, predicted mechanical properties are compared with data given by the Euro-Composite company and with results coming from crushing tests performed on sandwich specimens. This study brings out a powerful tool for the determination of the mechanical properties of most Nomex® honeycomb core used in nautical construction. The design of oceanic sailing race boats is one of its most outstanding practical applications