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Pre-impregnated thermoplastic composites are widely used in the aerospace industry for their excellent mechanical properties, impact resistance and fatigue strength all at lower density than other common materials. In recent years, the automotive industry has shown increasing interest in the manufacturing processes of thermoplastic-matrix composites materials, especially in thermoforming techniques for their rapid cycle times and the possible use of preexisting equipment. An important step in the prediction of the mechanical properties and technical feasibility of parts with complex geometry is the use of modelling and numerical simulations of these forming processes which can also be capitalized to optimize manufacturing practices. This paper aims to present an approach to the simulation of thermoplastic prepreg composites forming. The proposed model is based on convolution integrals defined under the principles of irreversible thermodynamics and within a hyperelastic framework. The hyperelastic potential is built from the contribution of four major deformation modes that assumed independent: the elongation in the warp and weft directions, the in-plane shear, and the bending deformations. Consequently the corresponding strain energy potentials which are uncoupled can be identified by classical tests on textile composite shells, such as tension, in plane-shear and bending tests. The viscoelasticity is introduced exclusively for the in-plane shear mode. The simulation is composed of thermal analyses and forming simulations performed alternatively. This ensures a coupling between the mechanical and thermal simulations. The deformation of a unit cell and the modification of contacts with the tools change the local thermal properties and temperatures. The thermal conductivities are determined by mesoscopic analysis.The woven reinforced prepreg has a periodicity that can be exploited to perform a homogenization simulation and get the macroscopic conductivity from the geometry of the mesostructure and from the thermal properties of the yarns and the polymer [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the instability of a viscoelastic fluid in a saturated porous medium heated from below and subjected to an horizontal through-flow. The Oldroyd-B constitutive equation is used to describe the viscoelastic behavior of diluted polymeric solutions. In the absence of the horizontal flow, the onset of convection can be characterized either by stationary or oscillatory instabilities. A temporal stability analysis is carried out in order to study the combined influence of the viscoelastic properties of the fluid and the main flow on the linear characteristics of these two types of instabilities. It is shown that the presence of the through-flow has a destabilizing effect and that it favors the emergence of mobile transverse rolls (R.T.), among an infinity of three-dimensional unstable modes. The thresholds for the appearance of these R.T., as well as their wavelengths and frequencies, are determined as functions of the dimensionless parameters of the problem. [Copyright &y& Elsevier]

The behaviour of dynamical systems is modified by the use of viscoelastic materials. In order to lead realistic complex eigenvalues analysis on dynamical systems, one need to model the behaviour of viscoelastic materials. The experiments show that the stiffness and the damping of such materials are frequency dependent. A large number of models often used are not able to describe this dependence; this is why the generalised Maxwell's model has been chosen. This paper describes a method based on modulus and angle curves to identify the parameters of this model. Between all the different formulations of generalized Maxwell, the pole-zero formulation is the most suited to lead the identification. However, some formulas allow to find the parameters of others formulations like the Prony one. The identification method presented here is based on the asymptotic curves of generalised Maxwell's model. This identification is led in two step, first parameters are initialised and second they are optimised. This method is confronted to others ones. If several viscoelastic materials have to be modelled in the same dynamical system, the size of the finite element model grows as quick as the number of poles. A way to reduce this size consists in constraining the poles to be equal for all materials. The method presented in this paper allows to perform the identification by taking this new constraint into account. [ABSTRACT FROM AUTHOR]

Abstract: In this Note, we prove a Carleman''s estimate for the integro-differential hyperbolic system of the viscoelasticity problem and we use this estimate to obtain a stability result for the inverse problem of recovering a viscoelastic coefficient from a unique internal measure. To cite this article: M. de Buhan, A. Osses, C. R. Acad. Sci. Paris, Ser. I 347 (2009). [Copyright &y& Elsevier]

A visco-elastic model for polymeric foams under cyclic compression. A block of polyurethane foam subject to cyclic compression exhibits a softening phenomenon as the number of cycles increases. In particular, one observes a stepping down of the loading curves while the unloading curves remain the same. In tests performed by the authors, it has been observed a partial recovery of the initial stiffness after a resting period was observed. This behaviour can be described as a long memory effect. We propose a viscoelastic model, coupling a non convex energy with a dissipation of viscous type. The model is in a good qualitative agreement with the experiments. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study is to contribute to the knowledge of viscoelastic fluids flows in a contraction which are often studied numerically. A device has been conceived for an experimental study of the flow by Laser Doppler velocimetry. An isothermal flow through a rectangular duct including an abrupt contraction has been considered. We have characterized the isothermal flow for different values of Reynolds number and correlations of the axial velocity are presented. To cite this article: M. Mahfoud et al., C. R. Mecanique 336 (2008). [Copyright &y& Elsevier]

Abstract: The viscoelastic generalization of T and A integrals is presented in this Note. The analytical developments are based on conservative laws, the non-dependent integrals and the combination of real and virtual displacement and thermals fields inducing a quadrilinear form of the strain energy density. In order to simulate this integral parameter by finite element software, a modeling form ensuring the non-dependent path integral during crack growth process is presented. The introducing of viscoelastic behavior is realized with the generalized Kelvin Voigt model. To cite this article: R. Moutou Pitti et al., C. R. Mecanique 336 (2008). [Copyright &y& Elsevier]

The interaction between a flowing fluid and the transmission mains is in relation with the applied pressure level as well as the sought structure lifetime. The numerical approach developed in this study is based on a global modeling of the fluid and the deformation of the duct under transient conditions. The viscous tangential stress is expressed using a mixed polynomial development representing the variation of the radial profile of the fluid speed. The resolution of the obtained system of equations is carried out using the method of the characteristics coupled with the finite differences method. In the case of a Newtonian fluid, the results were compared to the experimental data of Holmboe and the theoretical ones of Zielke. This comparison allowed confirming the validity of the adopted calculation scheme. An extension of calculations in a similar way was carried out for the same installation in the case of a linear viscoelastic fluid. [ABSTRACT FROM AUTHOR]

In this paper, the possibility of reducing pressure surges in a quasi-rigid pipe network by replacing one of the pipes of the network by a viscoelastic one is examined. The mathematical model consists of a system of two hyperbolic, partial differential equations which are resolved by the method of characteristics using linear interpolation. The calculation at the network junctions is realised by resolving a linear system of equations including the manner various boundary conditions are introduced into the solution. The behaviour law of the viscoelastic pipe is described by the Kelvin-Voigt model. In order to simplify calculations, only the elastic element of this model is considered. For the applications, a constructed computer progrmn written in FORTRAN language is elaborated. The numerical results show the effect of the pipe wall elasticity on the damping of the pressure waves in the networks. [ABSTRACT FROM AUTHOR]

Abstract: The main purpose of this Note is the development of a new integral Mv separating mixed mode fracture during a crack growth process in a viscoelastic media. The mathematical developments are based on conservative laws, the independent path integrals and the combination of real and virtual displacement fields inducing a bilinear form of the strain energy density. The uncoupling fracture mode is based on a generalization of the virtual work principle. The introduction of the viscoelastic behavior through an incremental formulation of the free energy allows the generalization of this path independent path integral. To cite this article: R. Moutou Pitti et al., C. R. Mecanique 335 (2007). [Copyright &y& Elsevier]

Abstract: We present a Cosserat-based 3D–1D dimensional reduction for the viscoelastic finite strain model introduced by P. Neff. The reduced 1D model preserves observer invariance. We prove the existence and uniqueness of the solution of the reduced coupled minimization/evolution problem. To cite this article: J. Beyrouthy, C. R. Acad. Sci. Paris, Ser. I 345 (2007). [Copyright &y& Elsevier]

Abstract: In this note, one considers a 1-d.o.f. oscillator consisting of a mass and a viscoelastic spring, the rheology of which is represented by a generalized so-called Biot''s model with parameters. It is proved that its independent eigenmotions are of the following nature: two eigenmotions damped with or without oscillations (as in the case of classical viscous damping) and n eigenmotions damped without oscillations which are induced by the viscoelastic rheology. To cite this article: P. Muller, C. R. Mecanique 333 (2005). [Copyright &y& Elsevier]

Abstract: The aim of the present Note is to differentiate the relative contributions of the aggregation and the percolation phenomena to the viscoelastic behaviour of composites. This separation is performed through the development of a micromechanical model, by taking into account the percolation concept. To cite this article: P. Mélé et al., C. R. Mecanique 333 (2005). [Copyright &y& Elsevier]

A bone remodeling model taking into account the viscoelastic properties of the material is proposed. The nonlinear equations governing the evolution of the bone apparent density are solved by a finite difference method in the unidimensional case of a n-unit elements model. The results show the effects of the viscous damping on the structure for a controlled mechanical loading. To cite this article: S. Baïotto, M. Zidi, C. R. Mecanique 332 (2004). [Copyright &y& Elsevier]

This paper is concerned with incompressible viscoelastic fluids which obey a differential constitutive law of White–Metzner type. We establish the existence and uniqueness of local solutions in 3-D as well as the global existence of small solutions. We then deduce the existence and asymptotic stability of small periodic and stationary solutions. Finally, we prove that the 2-D results obtained in Hakim (J. Math. Anal. Appl. 185 (1994) 675–705) remain true without any restriction on the smallness of the retardation parameter which is the linking coefficient between the equation of velocity (Navier–Stokes equation) and the transport equation verified by the extra-stress tensor. To cite this article: L. Molinet, R. Talhouk, C. R. Acad. Sci. Paris, Ser. I 338 (2004). [Copyright &y& Elsevier]

Fatigue of bituminous asphalts is one of the main types of pavement destruction. This phenomenon was studied extensively in Europe (RILEM) and in the United States (SHRP). There are no standardized tests in Quebec to assess asphalt fatigue resistance. In France, a new approach based on the determination of damage rates due to fatigue has been developed for a tension–compression test on asphalt core samples to study their fatigue strength. This paper presents a summary of the knowledge on asphalt fatigue. Damage rate analyses, developed by the DGCB (Département de Génie Civil et du Bâtiment) of the ENTPE at Lyon, is detailed and applied to stone matrix asphalt (SMA). Results show the validity of the approach by damage and the good fatigue damage strength of the SMA. [ABSTRACT FROM AUTHOR]

We extend the previous work by Benallal et al. on the relationship between structure and rheological properties of linear polymer melts. The aim of this paper is to quantify the effect of the chemical structure on the viscoelastic properties. We show that these properties are governed by the monomer dimensions and the interaction energy. To cite this article: A. Allal et al., C. R. Physique 3 (2002) 1451–1458. [Copyright &y& Elsevier]

Let α be a positive number. The one-dimensional viscoelastic problem utt−uxx−αuxxt=f, x∈(−∞,0], t∈[0,+∞), with unilateral boundary conditions u(0,·)⩾0, (ux+αuxt)(0,·)⩾0, (u(ux+αuxt))(0,·)=0, can be reduced to the following variational inequality: λ1*w=g+b, w⩾0, b⩾0, 〈w,b〉=0. Here λˆ1(ω) is the causal determination of iω√ of 1+iαω. We show that the energy losses are purely viscous; this result is a consequence of the relation 〈w˙,b〉=0; since a priori, b is a measure and w˙ is defined only almost everywhere, this relation is not trivial. To cite this article: A. Petrov, M. Schatzman, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 983–988. [Copyright &y& Elsevier]