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Lucien Laiarinandrasana - One of the best experts on this subject based on the ideXlab platform.
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On the role of the spherulitic microstructure in fatigue damage of pure Polymer and glass-fiber reinforced Semi-Crystalline polyamide 6.6
International Journal of Fatigue, 2019Co-Authors: I. Raphael, Nicolas Saintier, G. Robert, J. Béga, Lucien LaiarinandrasanaAbstract:Understanding fatigue damage mechanisms in short fiber reinforced thermoplastics is a key issue in order to optimize material processing and propose physically based multiscale fatigue damage models. The present work aims at further understanding observations of fatigue damage in the polyamide 6.6 matrix with respect to its Semi-Crystalline structure. In this paper the Polymer and associated composite are tested in their ductile regime i.e. above the glass transition temperature. Tomographic and SEM observations are used in order to establish a damage scenario at the spherulitic scale. These observations prove that fatigue damage progresses by intra-spherulitic failure in their equatorial plane. Observations of the spherulite nuclei also evidence the oriented structure of the Semi-Crystalline Polymer induced by the injection-molding manufacturing process.
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Time dependent voiding mechanisms in polyamide 6 submitted to high stress triaxiality: experimental characterisation and finite element modelling
Mechanics of Time-Dependent Materials, 2018Co-Authors: Nathan Selles, Nicolas Saintier, Henry Proudhon, Andrew King, Lucien LaiarinandrasanaAbstract:Double notched round bars made of Semi-Crystalline Polymer polyamide 6 (PA6) were submitted to monotonic tensile and creep tests. The two notches had a root radius of 0.45 mm, which imposes a multiaxial stress state and a state of high triaxiality in the net (minimal) section of the specimens. Tests were carried out until the failure occurred from one of the notches. The other one, unbroken but deformed under steady strain rate or steady load, was inspected using the Synchrotron Radiation Computed Tomography (SRCT) technique. These 3D through thickness inspections allowed the study of microstructural evolution at the peak stress for the monotonic tensile test and at the beginning of the tertiary creep for the creep tests. Cavitation features were assessed with a micrometre resolution within the notched region. Spatial distributions of void volume fraction ( Vf $\mathit{Vf}$ ) and void morphology were studied. Voiding mechanisms were similar under steady strain rates and steady loads. The maximum values of Vf $\mathit{Vf}$ were located between the axis of revolution of the specimens and the notch surface and voids were considered as flat cylinders with a circular basis perpendicular to the loading direction. A model, based on porous plasticity, was used to simulate the mechanical response of this PA6 material under high stress triaxiality. Both macroscopic behaviour (loading curves) and voiding micro-mechanisms (radial distributions of void volume fraction) were accurately predicted using finite element simulations.
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Voiding mechanisms in Semi-Crystalline polyamide 6 during creep tests assessed by damage based constitutive relationships and finite elements calculations
International Journal of Plasticity, 2016Co-Authors: Nathan Selles, Nicolas Saintier, Lucien LaiarinandrasanaAbstract:Notched round bars made of a Semi-Crystalline Polymer, polyamide 6, were submitted to creep tests. In order to study the microstructural evolution of the material during creep deformation, these tests were stopped at two characteristic creep times: i) the end of the secondary creep stage, ii) the onset of the failure during the tertiary creep stage, allowing 3D through thickness Synchrotron Radiation Tomography (SRT)-inspections. This SRT-technique allowed features of the damage to be assessed at a micrometre resolution within the notched region, such as spatial distributions of void volume fraction and void heights and diameters. These deformation mechanisms have already been observed and studied during steady strain rate loading and a multi-mechanism model coupled with damage formulation proposed to simulate notched specimens submitted to tensile loads. This model, based on porous visco-plasticity, was used here to simulate the creep behaviour of this PA6 material. The optimization procedure has led to a set of material coefficients capable of reproducing both macroscopic behaviour (creep curves) and damage micro-mechanisms. The level of maximum damage within the material and the spatial distributions of void volume fraction obtained numerically were compared successfully to experiments and the Cauchy stress tensor has been proved to be related to the void deformation mechanisms.
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Comparison of voiding mechanisms in Semi-Crystalline polyamide 6 during tensile and creep tests
Polymer Testing, 2016Co-Authors: Nathan Selles, Thilo F. Morgeneyer, Henry Proudhon, Franck N'guyen, Wolfgang Ludwig, Lucien LaiarinandrasanaAbstract:Behaviour of a Semi-Crystalline Polymer, polyamide 6, described by loading curves, as well as necking and whitening phenomena, is related to its micro-structural evolution in terms of void morphology and distribution during both tensile and creep tests. Notched bars have been subjected to creep tests interrupted at the onset of the tertiary creep stage and at the onset of final rupture. Inspections of these specimens using Synchrotron Radiation Tomography have been coupled with statistical image analysis treatment to obtain spatial distributions of void length and void volume fraction. Cavitation mechanisms observed and quantified during creep and tensile tests were similar: from penny shaped voids (diameter larger than height) perpendicular to the drawing direction to cylindrical voids (diameter equal to the height) arranged in columns during the neck extension. The void volume fraction distributions along radial and axial directions presented an inverted parabolic profile with a maximum located at the centre of the sample. Keywords
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Comparative study of continuum damage mechanics and Mechanics of Porous Media based on multi-mechanism model on Polyamide 6 Semi-Crystalline Polymer
International Journal of Solids and Structures, 2015Co-Authors: M. Jeridi, Lucien Laiarinandrasana, Kacem SaiAbstract:The biphasic character of Semi-Crystalline Polymer was modeled by the multi-mechanism (MM) constitutive relationships. Here, a comparative study between continuum damage mechanics (CDM) theory and Mechanics of Porous Media (MPM) approach, both related to the MM model, is performed. This comparison is based upon creep tests conducted on notched round bars made of PA6 Semi-Crystalline Polymer to enhance a multiaxial stress state. For CDM model, the damage is classically described by a unique overall variable whereas the average of the local porosity at each phase level was considered for the MPM model. For each model, the optimization of the set of material’s parameters was carried out by combining the overall behavior of notched specimens subjected to creep loading, as well as the local information such as the distribution of porosity. It is found that both CDM and MPM models, each coupled with MM model correctly describe the overall creep behavior of the notched specimen if two damage variables are used. Moreover the MM/MPM model is more relevant for predicting porosity distribution.
Moussa Nait-abdelaziz - One of the best experts on this subject based on the ideXlab platform.
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Effect of UV Ageing on the fatigue life of bulk polyethylene
2018Co-Authors: Hamza Lamnii, Georges Ayoub, U. Maschke, Moussa Nait-abdelaziz, Jean-michel Gloaguen, Bilal MansoorAbstract:Polymers operating in various weathering conditions must be assessed for lifetime performance. Particularly, ultraviolet (UV) radiations alters the chemical structure and therefore affect the mechanical and fatigue properties. The UV irradiation alters the Polymer chemical structure, which results into a degradation of the mechanical and fatigue behavior of the Polymer. The Polymer properties degradation due to UV irradiation is the result of a competitive process of chain scission versus post-crosslinking. Although few studied investigated the effect of UV irradiation on the mechanical behaviour of thermoplastics, fewer examined the UV irradiation effect on the fatigue life of Polymers. This study focuses on investigating the effect of UV irradiation on the fatigue properties of bulk Semi-Crystalline Polymer; the low density Polyethylene (LDPE). Tensile specimens were exposed to different dose values of UV irradiation then subjected to fatigue loading. The fatigue tests were achieved under constant stress amplitude at a frequency of 1Hz. The results show an important decrease of the fatigue limit with increasing absorbed UV irradiation dose.
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Large-strain viscoelastic-viscoplastic constitutive modeling of Semi-Crystalline Polymers and model identification by deterministic/evolutionary approach
Computational Materials Science, 2014Co-Authors: Hemin Abdul-hameed, Tanguy Messager, Fahmi Zaïri, Moussa Nait-abdelazizAbstract:Above the glass transition temperature, a Semi-Crystalline Polymer can behave like an elastomer or a stiff Polymer according to the crystal content. For a reliable design of such Polymeric materials, it is of prime importance to dispose a unified constitutive modeling able to capture the transition from thermoplastic-like to elastomeric-like mechanical response, as the crystal content changes. This work deals with polyethylene materials containing a wide range of crystal fractions, stretched under large strains at room temperature and different strain rates. A large-strain viscoelastic-viscoplastic approach is adopted to describe the mechanical response of these Polymers. In order to identify the model parameters, an analytical deterministic scheme and a practical, "engineering-like", numerical tool, based on a genetic algorithm are developed. A common point of manipulated constitutive models is that the elementary deformation mechanisms are described by two parallel resistances; one describes the intermolecular interactions and the other deals with the molecular network stretching and orientation process. In a first approach, the Semi-Crystalline Polymers are considered as homogeneous media; at each crystal content, the Semi-Crystalline Polymer is thus considered as a new material and a new set of model parameters is provided. In a second approach, the Semi-Crystalline Polymer is seen as a two-phase composite, and the effective contribution of the crystalline and amorphous phases to the overall mechanical response is integrated in the constitutive model, which allows simulating the transition from thermoplastic-like to elastomeric-like mechanical response. In this case, one set of model parameters is needed, the only variable being the crystal volume fraction. The identification results obtained using deterministic and numerical methods are discussed.
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Large-strain viscoelastic–viscoplastic constitutive modeling of Semi-Crystalline Polymers and model identification by deterministic/evolutionary approach
Computational Materials Science, 2014Co-Authors: Hemin Abdul-hameed, Tanguy Messager, Fahmi Zaïri, Moussa Nait-abdelazizAbstract:Abstract Above the glass transition temperature, a Semi-Crystalline Polymer can behave like an elastomer or a stiff Polymer according to the crystal content. For a reliable design of such Polymeric materials, it is of prime importance to dispose a unified constitutive modeling able to capture the transition from thermoplastic-like to elastomeric-like mechanical response, as the crystal content changes. This work deals with polyethylene materials containing a wide range of crystal fractions, stretched under large strains at room temperature and different strain rates. A large-strain viscoelastic–viscoplastic approach is adopted to describe the mechanical response of these Polymers. In order to identify the model parameters, an analytical deterministic scheme and a practical, “engineering-like”, numerical tool, based on a genetic algorithm are developed. A common point of manipulated constitutive models is that the elementary deformation mechanisms are described by two parallel resistances; one describes the intermolecular interactions and the other deals with the molecular network stretching and orientation process. In a first approach, the Semi-Crystalline Polymers are considered as homogeneous media; at each crystal content, the Semi-Crystalline Polymer is thus considered as a new material and a new set of model parameters is provided. In a second approach, the Semi-Crystalline Polymer is seen as a two-phase composite, and the effective contribution of the crystalline and amorphous phases to the overall mechanical response is integrated in the constitutive model, which allows simulating the transition from thermoplastic-like to elastomeric-like mechanical response. In this case, one set of model parameters is needed, the only variable being the crystal volume fraction. The identification results obtained using deterministic and numerical methods are discussed.
Hemin Abdul-hameed - One of the best experts on this subject based on the ideXlab platform.
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Explicit integration methods for constitutive equations of a mean-stress dependent elastoviscoplastic model : impact on structural finite element analyses
Engineering with Computers, 2021Co-Authors: Hemin Abdul-hameed, Laurent Cangémi, Eléonore Roguet, Nadège Brusselle-dupend, Habiba Boulharts, Abdul-hameed Hemin, Roguet Eléonore, Brusselle-dupend Nadège, Boulharts Habiba, Cangémi LaurentAbstract:The strong dependent behavior of Semi-Crystalline Polymers can lead to the use of simplified material laws in finite element structural calculations for reasons of robustness to the detriment of the quantitative response of the models. This work focuses on numerical integration methods as a solution to overcome the possible convergence and robustness limitations of mean-stress dependent elastoviscoplastic material laws, typical of the Semi-Crystalline Polymers’ mechanical behavior. What is proposed here is a rational application of three explicit integration methods (fourth- and second-order Runge–Kutta method, a hybrid schema between Runge–Kutta, and Euler method) in engineering structural calculations, which provide a reliable solution for constitutive models of Semi-Crystalline Polymer. These methods are examined for structure creep test and tensile test, in comparison with experimental data. The investigations have been done in terms of the stability toward convergence, the accuracy of results, the plastic consistency, and CPU time efficiency. This work, proposes an easy implementation of integration methods in any computational finite element code. It also provides a flexible modular implementation which is applicable to any different constitutive equations. An integration step sub-division technique is recommended. It is a powerful technique to improve the convergence of solution and accuracy of result by damping oscillation around stress Gauss point integration solution. The results obtained illustrate the effect of numerical integration schemas on structural analysis and provide an insight into select suitable method.
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Large-strain viscoelastic-viscoplastic constitutive modeling of Semi-Crystalline Polymers and model identification by deterministic/evolutionary approach
Computational Materials Science, 2014Co-Authors: Hemin Abdul-hameed, Tanguy Messager, Fahmi Zaïri, Moussa Nait-abdelazizAbstract:Above the glass transition temperature, a Semi-Crystalline Polymer can behave like an elastomer or a stiff Polymer according to the crystal content. For a reliable design of such Polymeric materials, it is of prime importance to dispose a unified constitutive modeling able to capture the transition from thermoplastic-like to elastomeric-like mechanical response, as the crystal content changes. This work deals with polyethylene materials containing a wide range of crystal fractions, stretched under large strains at room temperature and different strain rates. A large-strain viscoelastic-viscoplastic approach is adopted to describe the mechanical response of these Polymers. In order to identify the model parameters, an analytical deterministic scheme and a practical, "engineering-like", numerical tool, based on a genetic algorithm are developed. A common point of manipulated constitutive models is that the elementary deformation mechanisms are described by two parallel resistances; one describes the intermolecular interactions and the other deals with the molecular network stretching and orientation process. In a first approach, the Semi-Crystalline Polymers are considered as homogeneous media; at each crystal content, the Semi-Crystalline Polymer is thus considered as a new material and a new set of model parameters is provided. In a second approach, the Semi-Crystalline Polymer is seen as a two-phase composite, and the effective contribution of the crystalline and amorphous phases to the overall mechanical response is integrated in the constitutive model, which allows simulating the transition from thermoplastic-like to elastomeric-like mechanical response. In this case, one set of model parameters is needed, the only variable being the crystal volume fraction. The identification results obtained using deterministic and numerical methods are discussed.
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Large-strain viscoelastic–viscoplastic constitutive modeling of Semi-Crystalline Polymers and model identification by deterministic/evolutionary approach
Computational Materials Science, 2014Co-Authors: Hemin Abdul-hameed, Tanguy Messager, Fahmi Zaïri, Moussa Nait-abdelazizAbstract:Abstract Above the glass transition temperature, a Semi-Crystalline Polymer can behave like an elastomer or a stiff Polymer according to the crystal content. For a reliable design of such Polymeric materials, it is of prime importance to dispose a unified constitutive modeling able to capture the transition from thermoplastic-like to elastomeric-like mechanical response, as the crystal content changes. This work deals with polyethylene materials containing a wide range of crystal fractions, stretched under large strains at room temperature and different strain rates. A large-strain viscoelastic–viscoplastic approach is adopted to describe the mechanical response of these Polymers. In order to identify the model parameters, an analytical deterministic scheme and a practical, “engineering-like”, numerical tool, based on a genetic algorithm are developed. A common point of manipulated constitutive models is that the elementary deformation mechanisms are described by two parallel resistances; one describes the intermolecular interactions and the other deals with the molecular network stretching and orientation process. In a first approach, the Semi-Crystalline Polymers are considered as homogeneous media; at each crystal content, the Semi-Crystalline Polymer is thus considered as a new material and a new set of model parameters is provided. In a second approach, the Semi-Crystalline Polymer is seen as a two-phase composite, and the effective contribution of the crystalline and amorphous phases to the overall mechanical response is integrated in the constitutive model, which allows simulating the transition from thermoplastic-like to elastomeric-like mechanical response. In this case, one set of model parameters is needed, the only variable being the crystal volume fraction. The identification results obtained using deterministic and numerical methods are discussed.
Xavier Colin - One of the best experts on this subject based on the ideXlab platform.
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Experimental investigation and modeling attempt on the effects of ultraviolet aging on the fatigue behavior of an LDPE Semi-Crystalline Polymer
International Journal of Fatigue, 2021Co-Authors: Hamza Lamnii, Moussa Nait-abelaziz, Georges Ayoub, Xavier Colin, U. MaschkeAbstract:The objective of this study was to investigate the effect of UV irradiation on the fatigue life of a bulk Semi-Crystalline Polymer. Low-density polyethylene samples exposed to different UV irradiation doses were fatigue tested. Fatigue indicator based on dissipated energy per cycle was found to present the best correlation with the experimental fatigue results. A master curve unifying the experimental fatigue results for as-received and UV-aged materials was obtained when subtracting the dissipated energy threshold from the total dissipated energy. Finally, the evolution of the damage with cyclic loading was analyzed and preliminary modeling was attempted.
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modeling the visco hyperelastic viscoplastic behavior of photodegraded semi crystalline low density polyethylene films
International Journal of Solids and Structures, 2020Co-Authors: Georges Ayoub, Bilal Mansoor, Ana K Rodriguez, Xavier ColinAbstract:Abstract In this work we propose to model the mechanical and fracture response of Semi-Crystalline low-density polyethylene (LDPE) films exposed to accelerated ultraviolet (UV) ageing using a physically based visco-hyperelastic–viscoplastic approach. UV irradiation induces an alteration of the chemical and structural properties of the Semi-Crystalline Polymer, which affects significantly its mechanical behavior. In this work, pristine and oxidized low-density polyethylene films are characterized by conventional physico-chemical and mechanical techniques (FTIR spectroscopy, DSC, HT-GPC, and uniaxial tensile testing). Polyethylene exhibits an oxidation-induced strengthening for a low range of UV radiation doses and a cavitation-induced softening for higher UV radiation doses. A competing multi-scale phenomena induced by UV radiation are incorporated into the constitutive model to capture the macroscopically observed mechanical and fracture behavior. Namely, the model will incorporate at the nano scale, chain scissions and cross-linking and at the meso and macro scales, oxidation-induced cracking, chemi-crystallization, and mechanical damage. The model used the high-temperature gel permeation chromatography-measured molecular weight as degradation indicator. The model was able to capture accurately the evolution of the macroscopically observed mechanical and fracture behavior over a wide range of UV irradiation doses.
Kacem Sai - One of the best experts on this subject based on the ideXlab platform.
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Comparative study of continuum damage mechanics and Mechanics of Porous Media based on multi-mechanism model on Polyamide 6 Semi-Crystalline Polymer
International Journal of Solids and Structures, 2015Co-Authors: M. Jeridi, Lucien Laiarinandrasana, Kacem SaiAbstract:The biphasic character of Semi-Crystalline Polymer was modeled by the multi-mechanism (MM) constitutive relationships. Here, a comparative study between continuum damage mechanics (CDM) theory and Mechanics of Porous Media (MPM) approach, both related to the MM model, is performed. This comparison is based upon creep tests conducted on notched round bars made of PA6 Semi-Crystalline Polymer to enhance a multiaxial stress state. For CDM model, the damage is classically described by a unique overall variable whereas the average of the local porosity at each phase level was considered for the MPM model. For each model, the optimization of the set of material’s parameters was carried out by combining the overall behavior of notched specimens subjected to creep loading, as well as the local information such as the distribution of porosity. It is found that both CDM and MPM models, each coupled with MM model correctly describe the overall creep behavior of the notched specimen if two damage variables are used. Moreover the MM/MPM model is more relevant for predicting porosity distribution.
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multi mechanism damage plasticity model for semi crystalline Polymer creep damage of notched specimen of pa6
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011Co-Authors: Kacem Sai, Lucien Laiarinandrasana, M. Jeridi, Ben I Naceur, Jacques Besson, Georges CailletaudAbstract:Research highlights ▶ Study of mechanical and damage behaviour of Semi-Crystalline Polymer (PA6). ▶ Generalize a multimechanism model to account for mechanical damage behaviour of PA6. ▶ Predict the overall behaviour as well as the local behaviour. ▶ Reproduce the location of the maximum damage in a structure (finite element method). ▶ Lifetime prediction of PA6 components (pressure vessel, pipes) under creep loading. Abstract The multi-mechanism model devoted to the Semi-Crystalline Polymers proposed in the recent study (Regrain et al. [1] ) is generalized in this work to account for mechanical damage behaviour. To assess model reliability, finite element simulations of notched specimens subjected to creep behaviour were performed and compared successfully to experiments in terms of creep notch opening displacement. The model is able to reproduce the location of the maximum damage in a structure. This is a key information for the lifetime prediction of engineering components made of Semi-Crystalline Polymers such as pressure vessel or pipes subjected to creep loading.
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Multi-mechanism damage-plasticity model for Semi-Crystalline Polymer: Creep damage of notched specimen of PA6
Materials Science and Engineering: A, 2011Co-Authors: Kacem Sai, Lucien Laiarinandrasana, M. Jeridi, Jacques Besson, I. Ben Naceur, Georges CailletaudAbstract:The multi-mechanism model devoted to the Semi-Crystalline Polymers proposed in the recent study (Regrain et al. [1]) is generalized in this work to account for mechanical damage behaviour. To assess model reliability, finite element simulations of notched specimens subjected to creep behaviour were performed and compared successfully to experiments in terms of creep notch opening displacement. The model is able to reproduce the location of the maximum damage in a structure. This is a key information for the lifetime prediction of engineering components made of Semi-Crystalline Polymers such as pressure vessel or pipes subjected to creep loading.
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Multi-mechanism models for Semi-Crystalline Polymer: Constitutive relations and finite element implementation
International Journal of Plasticity, 2009Co-Authors: Cédric Regrain, Lucien Laiarinandrasana, Sophie Toillon, Kacem SaiAbstract:Two multi-phase models called 2M1C and 2M2C which take the degree of crystallinity into account were investigated with the help of tensile and creep test database of Polyamide 6 (PA6) material. Multi-phase models are based on the localization of the stress and the homogenization of the local viscoplastic strains. The two models differ mainly by the supplementary coupling introduced in the 2M1C model by means of the flow expression. The first objective of this work is to select which one of the two models is more appropriate for the description of the PA6 mechanical behaviour. The constitutive relations are presented and the finite element (FE) implementation is discussed. The creep strain rate versus applied stress curves are well simulated by both models. The only difference can be detected at the phase level where the creep strain and the creep strain rates differ in their evolution. The models can be extended to any Semi-Crystalline Polymer. Experimental data from the literature are selected to assess the models capabilities to account for the crystallisation kinetics controlled by the strain level.
