Time filter

Source Type

Guskov M.,CNRS Process and Engineering in Mechanics and Materials Laboratory | Thouverez F.,CNRS Tribology and Dynamic Systems Laboratory
Journal of Vibration and Acoustics, Transactions of the ASME | Year: 2012

Quasi-periodic motions and their stability are addressed from the point of view of different harmonic balance-based approaches. Two numerical methods are used: a generalized multidimensional version of harmonic balance and a modification of a classical solution by harmonic balance. The application to the case of a nonlinear response of a Duffing oscillator under a bi-periodic excitation has allowed a comparison of computational costs and stability evaluation results. The solutions issued from both methods are close to one another and time marching tests showing a good agreement with the harmonic balance results confirm these nonlinear responses. Besides the overall adequacy verification, the observation comparisons would underline the fact that while the 2D approach features better performance in resolution cost, the stability computation turns out to be of more interest to be conducted by the modified 1D approach. © 2012 American Society of Mechanical Engineers.

Richaud E.,CNRS Process and Engineering in Mechanics and Materials Laboratory | Flaconneche B.,French Institute of Petroleum | Verdu J.,CNRS Process and Engineering in Mechanics and Materials Laboratory
Polymer Testing | Year: 2012

This paper reports solubility and diffusivity data for soy and rapeseed methyl esters in polyethylene together with comparisons with methyl oleate and linoleate. These data showed that there is no significant difference in diffusivity and solubility between all these penetrants. Data were used to discuss the reliability of predictive models for diffusion and solubility of additive type molecules into semi-crystalline thermoplastic polymers. Permeability data were monitored by a new device, the results from which are in reasonable agreement with theoretical considerations on solubility and diffusivity. They also showed that biodiesels are less aggressive towards polyethylene than diesel from a petrochemical source. © 2012 Elsevier Ltd. All rights reserved.

Mareau C.,Arts et Metiers ParisTech | Favier V.,CNRS Process and Engineering in Mechanics and Materials Laboratory | Weber B.,ArcelorMittal | Galtier A.,CETIM 52 | Berveiller M.,Arts et Metiers ParisTech
International Journal of Plasticity | Year: 2012

A micromechanical model is proposed to describe the interactions between the microstructure and the dissipative deformation mechanisms in ferritic steels under cyclic loading. The model aims at optimizing the microstructure of steels since the dissipative mechanisms can be responsible for the initiation of microcracks. Therefore, a better understanding of the influence of the microstructure could lead to an improvement of fatigue properties. The dissipative mechanisms are assumed to be either anelastic (dislocation oscillations) or inelastic (plastic slip) and are described at the scale of the slip system using the framework of crystal plasticity. The macroscopic behavior is then deduced with a homogenization scheme. The model is validated by comparing the simulations with experimental results and is finally used to predict the impact of different microstructure parameters on the heat dissipation. © 2011 Elsevier Ltd. All rights reserved.

Laamouri A.,University of Sousse | Sidhom H.,University of Tunis | Braham C.,CNRS Process and Engineering in Mechanics and Materials Laboratory
International Journal of Fatigue | Year: 2013

This paper is aimed at evaluating the residual stress relaxation and its effect on the fatigue strength of AISI 316L steel ground surfaces in comparison to electro-polished surfaces. An experimental evaluation was performed using 3-point and 4-point bending fatigue tests at Rσ = 0.1 on two sets of notched specimens finished by electro-polishing and grinding. The residual stress fields were measured at the notch root of specimens, before and after fatigue tests, by means of the X-ray diffraction technique. It was found a degradation of about -35% for the 4-point bending fatigue limit at 2 × 106 cycles of the ground specimens in comparison to the electro-polished ones. This degradation is associated with a slight relaxation of the grinding residual stresses which remain significant tensile stresses at the stabilized state. While under the 3-point bending test, these residual stresses relax completely and provoke a noticeable increase of the fatigue limit estimated at about 50% in comparison to the 4-point bending fatigue test. The numerical evaluation of residual stress relaxation was carried out by FE analyses of the cyclic hardening behaviour of the ground layer. The isotropic and nonlinear kinematic model proposed by Chaboche was used and calibrated for the base material and the ground layer. The results show that residual stresses relax to a stabilized state characterized by elastic-shakedown response. This stabilization is occurred after the first cycle of the 4-point bending test corresponding to the higher stress concentration (Kt-4p = 1.66), while it requires many cycles under the 3-point bending test corresponding to the lower stress concentration (Kt-3p = 1.54). The incorporation of stabilized residual stress values into the Dang Van's criterion has permitted to predict with an acceptable accuracy the fatigue limits under both bending modes. © 2012 Elsevier Ltd. All rights reserved.

Richaud E.,CNRS Process and Engineering in Mechanics and Materials Laboratory
Radiation Physics and Chemistry | Year: 2014

This paper reports a compilation of data for PE+Vitamin E and 2,6-di-tert-butylphenols oxidation in radio-thermal ageing. Data unambiguously show that Vitamin E reacts with P and POO whereas 2,6-di-tert-butyl phenols only react with POO. Kinetic parameters of the stabilization reactions for both kinds of antioxidants were tentatively extracted from phenol depletion curves, and discussed regarding the structure of the stabilizer. They were also used for completing an existing kinetic model used for predicting the stabilization by antioxidants. This one permits to compare the efficiency of stabilizer with dose rate or sample thickness. © 2014 Elsevier Ltd.

Cruz C.,CNRS Process and Engineering in Mechanics and Materials Laboratory | Chinesta F.,École Centrale Nantes | Regnier G.,CNRS Process and Engineering in Mechanics and Materials Laboratory
Archives of Computational Methods in Engineering | Year: 2012

Kinetic theory is a mathematical framework intended to relate directly the most relevant characteristics of the molecular structure to the rheological behavior of the bulk system. In other words, kinetic theory is a micro-to-macro approach for solving the flow of complex fluids that circumvents the use of closure relations and offers a better physical description of the phenomena involved in the flow processes. Cornerstone models in kinetic theory employ beads, rods and springs for mimicking the molecular structure of the complex fluid. The generalized bead-rod-spring chain includes the most basic models in kinetic theory: the freely jointed bead-spring chain and the freely-jointed bead-rod chain. Configuration of simple coarse-grained models can be represented by an equivalent Fokker-Planck (FP) diffusion equation, which describes the evolution of the configuration distribution function in the physical and configurational spaces. FP equation can be a complex mathematical object, given its multidimensionality, and solving it explicitly can become a difficult task. Even more, in some cases, obtaining an equivalent FP equation is not possible given the complexity of the coarse-grained molecular model. Brownian dynamics can be employed as an alternative extensive numerical method for approaching the configuration distribution function of a given kinetic-theory model that avoid obtaining and/or resolving explicitly an equivalent FP equation. The validity of this discrete approach is based on the mathematical equivalence between a continuous diffusion equation and a stochastic differential equation as demonstrated by Itô in the 1940s. This paper presents a review of the fundamental issues in the BD simulation of the linear viscoelastic behavior of bead-rod-spring coarse grained models in dilute solution. In the first part of this work, the BD numerical technique is introduced. An overview of the mathematical framework of the BD and a review of the scope of applications are presented. Subsequently, the links between the rheology of complex fluids, the kinetic theory and the BD technique are established at the light of the stochastic nature of the bead-rod-spring models. Finally, the pertinence of the present state-of-the-art review is explained in terms of the increasing interest for the stochastic micro-to-macro approaches for solving complex fluids problems. In the second part of this paper, a detailed description of the BD algorithm used for simulating a small-amplitude oscillatory deformation test is given. Dynamic properties are employed throughout this work to characterise the linear viscoelastic behavior of bead-rod-spring models in dilute solution. In the third and fourth part of this article, an extensive discussion about the main issues of a BD simulation in linear viscoelasticity of diluted suspensions is tackled at the light of the classical multi-bead-spring chain model and the multi-bead-rod chain model, respectively. Kinematic formulations, integration schemes and expressions to calculate the stress tensor are revised for several classical models: Rouse and Zimm theories in the case of multi-bead-spring chains, and Kramers chain and semi-flexible filaments in the case of multi-bead-rod chains. The implemented BD technique is, on the one hand, validated in front of the analytical or exact numerical solutions known of the equivalent FP equations for those classic kinetic theory models; and, on the other hand, is control-set thanks to the analysis of the main numerical issues involved in a BD simulation. Finally, the review paper is closed by some concluding remarks. © 2012 CIMNE, Barcelona, Spain.

Diani J.,CNRS Process and Engineering in Mechanics and Materials Laboratory
Rubber Chemistry and Technology | Year: 2016

Directional laws, also called micro-sphere laws, are based on the rubber elasticity theory and are designed to fit rubber mechanical stress-strain responses at large strain. Because they depend on material directions, directional changes may be introduced accounting for anisotropic damage or residual stretch such as resulting from Mullins softening or accounting for anisotropic strain hardening such as induced by crystallization. Directional laws provide a relevant alternative to strain invariants laws when the material isotropy evolves or when its anisotropy is difficult to guess a priori. In the current contribution, the building process involved when defining directional laws is presented. The major assumptions resulting from this process are reviewed. Finally, recent directional laws from the literature are discussed, highlighting the interest and potential of such a constitutive framework.

Richaud E.,CNRS Process and Engineering in Mechanics and Materials Laboratory
European Polymer Journal | Year: 2013

Irganox 1010 stabilized PE was monitored by carbonyl build-up and DSC under oxygen. A scheme for PE stabilization by phenols was implemented and its kinetic parameters were calculated from experimental results. This model was validated from its ability to simulate kinetics curves for carbonyl build up, induction period changes with stabilizer concentration, and stabilizer depletion curve in thermal ageing. The use of OIT measurement for quantifying stabilizer is also discussed. Kinetic analysis showed that OIT is actually proportional to stabilizer concentration in virgin samples but this is not true for aged samples because of negative influence of oxidation unstable by-products. The model was also employed for discussing some scenarii proposed as explanation of heterogeneity observed during thermal oxidation of stabilized polyolefins. © 2013 Elsevier Ltd. All rights reserved.

Ranc N.,CNRS Process and Engineering in Mechanics and Materials Laboratory | Palin-Luc T.,Arts et Metiers ParisTech | Paris P.C.,Arts et Metiers ParisTech
Engineering Fracture Mechanics | Year: 2011

Plastic dissipation at the crack tip under cyclic loading is responsible for the creation of an heterogeneous temperature field around the crack tip. A thermomechanical model is proposed in this paper for the theoretical problem of an infinite plate with a semi-infinite through crack under mode I cyclic loading both in plane stress or in plane strain condition. It is assumed that the heat source is located in the reverse cyclic plastic zone. The proposed analytical solution of the thermo-mechanical problem shows that the crack tip is under compression due to thermal stresses coming from the heterogeneous stress field around the crack tip. The effect of this stress field on the stress intensity factor (its maximum and its range) is calculated analytically for the infinite plate and by finite element analysis. The heat flux within the reverse cyclic plastic zone is the key parameter to quantify the effect of dissipation at the crack tip on the stress intensity factor. © 2010 Elsevier Ltd.

Fitoussi J.,CNRS Process and Engineering in Mechanics and Materials Laboratory | Bocquet M.,CNRS Process and Engineering in Mechanics and Materials Laboratory | Meraghni F.,Arts et Metiers ParisTech
Composites Part B: Engineering | Year: 2013

This study investigates the origin of the strain rate effect on the mechanical behavior of a discontinuous glass fiber reinforced ethylene-propylene copolymer (EPC) matrix composite. This kind of composite materials are commonly used for automotive functional and structural applications. To this aim, a multi-scale experimental approach is developed. The deformation processes and the damage mechanisms observed at the microscopic scale are related to the material mechanical properties at the macroscopic scale. Tensile tests up to failure and specific interrupted tensile tests have been optimized and performed for high strain rates up to 200 s-1 to quantify the strain rate effect at different scales. High speed tensile tests have also been performed on the pure copolymer matrix. The threshold and the kinetic of damage have been quantified at both microscopic and macroscopic scales. Experimental results show that the composite behavior is strongly strain-rate dependent. The multi-scale analysis leads to the conclusion that the strain rate effect on the damage behavior of the EPC matrix composite is mainly due to the viscous behavior of the EPC matrix. SEM observations and analysis show that a localized deformation in the interface zone around fibers occurs at high strain rates and directly affects the visco-damage behavior. It is established that when the strain rate increases, the local deformation zone around the fibers behaves like a dissipation zone. Consequently, the damage initiation is delayed and the related kinetic is reduced with respect to the quasi-static loading case. © 2012 Elsevier Ltd. All rights reserved.

Loading CNRS Process and Engineering in Mechanics and Materials Laboratory collaborators
Loading CNRS Process and Engineering in Mechanics and Materials Laboratory collaborators