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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]

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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: 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]

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: 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]

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]