Model coupling friction and adhesion for steel-concrete interfaces

The interface behaviour between steel and concrete, during pull-out tests, is numerically investigated using an interface model coupling adhesion and Coulomb friction. This model, first developed by Raous, Cang\'emi, Cocou and Monerie (RCCM), is based on the adhesion intensity variable, introduced by Fr\'emond, which is a surface damage variable. The RCCM model is here completed by taking a variable friction coefficient to simulate the slip weakening of the interface when sliding occurs. Identification of the parameters and validation of the model are carried on pull out experiments conducted at the INSA of Toulouse on steel-concrete interface of reinforced concrete

Interface models coupling adhesion and friction

International audienceInterface models coupling friction and adhesion, where adhesion is regarded as interface damage, are briefly reviewed. The most widely used cohesive zone models are presented and discussed. A general framework for these laws, recently developed by Del Piero and Raous in the form of a unified model, is outlined. As an example, it is here established that the RCCM (Raous-Cangémi-Cocou-Monerie) model is a specific case in this general framework. The variational formulation and some associated solvers are briefly recalled in the context of non-smooth mechanics in the cases of both quasi-static and dynamic problems. A few examples in various fields of application are given. Lastly, some open problems and ongoing researches in this field are presented and discussed

Simulation numérique du comportement des mousses polymériques sous compression cyclique

National audienceDans cette communication on s'intéresse à la simulation numérique du comportement sous compression des mousses polymériques à porosité ouverte. On considère le modèle unidimensionnel introduit dans [1, 9], où la mousse est représentée par une chaîne des ressorts non linéaires endommageables avec une énergie des déformations non convexe, associés en parallèle avec des éléments viscoélastiques linéaires. La procédure d'identification des paramètres du modèle est détaillée. La comparaison entre les résultats des simulations numériques et les expériences montre que le modèle est capable de décrire le comportement des mousses pour différents trajets de charge en compression uniaxiale

Non linear elasticity, viscosity and damage in open-cell polymeric foams

International audienceOf interest in this work is the behavior of open-cell polymer foams under compression. In a recent work by Del Piero and Pampolini (2012) a model coupling non linear elasticity and viscosity was introduced to describe the response of a polyurethane foam subjected to uniaxial cyclic compression. Non elastic effects of the response curves were attributed to the viscous properties of the foam, while strain localization and hysterisis were attributed to the non convexity of the strain energy density. But the model could not reproduce the response curves after the first loading-unloading cycle. Here that model is extended by taking into account the damage of the foam. A simple phenomenological one parameter damage law is used to describe the damage of the cell walls occurring during the first loading cycle. An accurate identification procedure for the model constants is also developed and the mutual role played by viscosity and damage on the foam deformation evolution is discussed. Besides the one dimensional formulation, the model permits a precise analysis of the main phenomena which have to be considered to describe the complex behavior of the foam

A unified model for adhesive interfaces with damage, viscosity and friction

International audienceA general framework for models describing adhesive contact between rigid bodies is proposed. The intensity of adhesion is supposed to decrease under the action of prescribed tangential and normal relative displacements. The reduction is attributed to progressive damage, and comes with energy dissipation. Additional dissipation due to viscosity and friction is also taken into account. The response of the interface is described by a single state variable. It is determined by general laws expressing a mechanical version of the first two laws of thermodynamics, combined with a set of phenomenological assumptions

GRADIENT OF DAMAGE ENHANCEMENT FOR A COHESIVE MODEL

International audienceGradient enhancements have become increasingly popular in the last decades for dealing with problems in mechanics suffering from spurious mesh sensitivity induced by strain softening. Many proposals exist in this sense and various regularization techniques have been presented and successfully applied to study localization and fracture. In short, the idea underlying almost all such techniques is that of using some extended con-stitutive equations in which information about the material microstructure is represented through a length scale-related parameter. The physical interpretation of this quantity on a micromechanical basis is still the object of an open debate, whereby its interpretation as a mere numerical regularization parameter is certainly more appropriate. From a computational standpoint, once spatial gradients and/or length scales are introduced in the constitutive equations the latter are no longer defined at the local (quadra-ture point) level but they are established at a larger scale, i.e. the scale of the structural model, in a form that could be rephrased in an integral format. Basically, for usual local models stresses, strains and internal variables are defined in a point-wise fashion whereby, as outlined in [1], their values can be regarded as the parameters of a piece-wise constant interpolation. Hence, variables computed at the Gauss point level in classical displacement-based finite element methods can be understood as fields that are in general discontinuous across elements boundaries and inside elements as well. This discontinuous pattern is indeed one of the most striking consequences of the strictly local character of the constitutive law

Module GYPTIS version 1.0 : contact unilatéral avec frottement en mécanique des structures, inéquations variationnelles

Le module GYPTIS permet de résoudre des problèmes de con- tact unilatéral avec frottement de Coulomb entre une structure et un obstacle fixe ou entre différents solides déformables. Le problème est ici posé et résolu pour de petites déformations élastiques. L'extension à la viscoélasticité, la viscoplasticité ou l'élastoplasticité en grandes déformations a été réalisée par ailleurs (...

A Bipotential Method Coupling Contact, Friction and Adhesion

International audience– The paper is related to the analysis and the modeling of structural interface behaviors when unilateral contact, friction and adhesion interact. Among the contact models in literature, the model developed by Raous, Cangémi, Cocou and Monerie (RCCM model) is retained. It consists to include strict unilateral contact to avoid interpenetration, initial adhesion progressively decreases when the load increases, and Coulomb's friction which is progressively activated when adhesion decreases. Because of its implicit character, the Coulomb friction law with adhesion is non-associated, and the notion of superpotential with normality rule cannot be used anymore. In the present work, to overcome this non-associated character, a specific potential adapted to coupling unilateral contact, friction and adhesion is build and named bipotential. A numerical model is proposed and improved to solve the boundaries values problem. The algorithm is implemented in the finite element code SYMEF which has been developed at the University of Bechar (Algeria). A comparative study is made between the bipotential model and the previously developed RCCM model. The numerical results show that, this approach is robust and efficient in terms of numerical stability, precision convergence and CPU time compared to the RCCM model

Adhesive Contact : a Survey and a Unified Formulation

International audienceA brief survey of the most widely used Cohesive Zone Models is first presented and discussed. Then, a general framework for these laws is given under the form of a unified formulation recently proposed by Del Piero and Raous (Del Piero, Raous [1]). This unified formulation is based on : – general laws, typically, energy conservation and dissipation principles, that is, mechanical versions of the first two laws of thermodynamics, – a set of state variables, that is, an array of independent variables which fully determine the response to all possible deformation processes, – a set of elastic potential and dissipation potentials, which are functions of state in terms of which the general laws take specific forms, – a set of constitutive assumptions. The behavior of the interface is first characterized by two given loading curves f n (u n) and f t (u t) , which are supposed to be star-shaped with respect to the origin, where u n and u t are the normal and tangential components of the relative displacement on the interface and R n and R t are respectively the components of the contact force. A state variable α is introduced to measure the current intensity of damage. The variables {u n , u t , α} have to satisfy a set of inequalities which defines the state space. To exemplify this, for the special case where there is no viscosity, the loading curve R n =f n (u n) and the state space are given for the normal components in Fig.1 (a) and (b). The response due to a deformation process of loading-unloading starting from the origin is represented by the dashed line in the force-displacement plane (a) and in the state space (b). As described in [1], the strain energy is then given by : Ψ(u n , u t , α) = 1 2 g n (α)

Art of Modeling in Contact Mechanics

International audienceIn this chapter, we will first address general issues of the art and craft of modeling-contents, concepts, methodology. Then, we will focus on modeling in contact mechanics, which will give the opportunity to discuss these issues in connection with non-smooth problems. It will be shown that the non-smooth character of the contact laws raises difficulties and specificities at every step of the modeling process. A wide overview will be given on the art of mod-eling in contact mechanics under its various aspects: contact laws, their mechanical basics, various scales, underlying concepts, mathematical analysis, solvers, identification of the constitutive parameters and validation of the models. Every point will be illustrated by one or several examples. 1 Modeling: the bases It would be ambitious to try to give a general definition of the concept either of a model itself or of model processing. Modeling relates to the general process of production of scientific knowledge and also to the scientific method itself. It could be deductive (from the general to the particular, as privileged by Aristotle) or inductive (making sense of a corpus of raw data). Descartes (38) saw in the scientific method an approach to be followed step by step to get to a truth. Modeling can be effectively regarded as a scientific method that proceeds step by step, but its objective is more modest: to give sense of an observation or an experiment, and above all to predict behaviors within the context of specific assumptions. This concept of " proceeding step by step " is fundamental in modeling. In this first section, we will examine the notion of model in the general context of mechanical systems