Etudes éxprimentale de mélanges thermoplastiques/poudrettes de pneumatiques usagés

L'insertion de poudrettes (< 1 mm) de pneumatiques usagés (PUNR) issues de broyage dans une matrice thermoplastique (PP) est une voie de valorisation. Après formulation du mélange compatibilisé pour cinq taux de PUNR de 5% à 25%, des essais de traction ont été réalisés à trois vitesses de déformation (10-4, 10-3, 10-2 s-1). Des observations post-mortem (MEB et tomographie) permettent de comprendre les modes d'endommagement des éprouvettes. Les modèles micromécaniques, basés sur les opérateurs interfaciaux, sont utilisés pour identifier les critères d'endommagement de ce type de matériaux

Comportement macroscopique d'un élastomère renforcé : modélisations micro-macro et validation

Dans cette étude, nous proposons l'évaluation d'un modèle d'homogénéisation non linéaire appliqué aux composites hyperélastiques à microstructure aléatoire. Cette modélisation repose sur une mise en oeuvre, dans un contexte 3D, de la méthode du second ordre introduite par Ponte Castañeda & Tiberio (2000). Nous rappelons d'abord les principes de base de la méthode. Puis, nous étudions le cas d'un composite biphasé, constitué d'une matrice hyperélastique renforcée par des particules sphériques déformables. L'implémentation numérique du modèle micromécanique est discutée et les résultats obtenus sont présentés afin de démontrer l'effet de renforcement des particules. Afin de fournir une évaluation rigoureuse du modèle proposé, des calculs par éléments finis sur une cellule de base sont réalisés pour être comparés aux prédictions du modèle d'homogénéisation. Enfin, une confrontation aux données expérimentales montre la nécessité d'une prise en compte de phénomènes d'endommagement dans les modélisations ultérieures

An homogenization-based hyperelastic damage model: formulation and application to an EPDM/PP composite

The present Note concerns the formulation, implementation and a first application of a micromechanically based hyperelastic damage model. The approach is based on the second order homogenization method proposed by Lopez-Pamies and Ponte Castañeda (2000) for hyperelastic composites and recently developed by Lopez-Pamies and Ponte Castañeda (2007) in the case of porous elastomers. We first implement the method and proceed to its verification by comparison with Finite Element simulations on a unit cell. Taking advantage of this validation and by using standard thermodynamics arguments, we propose an hyperelastic damage model founded on voids growth phenomena. Finally, we provide an example of validation of the model by comparison with experimental data obtained on an EPDM/PP composite

Study of EPDM/PP polymeric blends: mechanical behavior and effects of compatibilization

International audienceA blend of Ethylene Propylene Diene Monomer (EPDM) rubber reinforced by polypropylene (PP) particles has been processed and its hyperelastic behavior has been characterized under cyclic uni-axial tensile tests. The experimental results show a significant effect of the fraction of polypropylene particles (10%, 25% and 30% by weight). Moreover, from another series of tests conducted on materials containing compatibilizers at different mass concentration, it is observed that the introduction of a compatibilizer increases the rigidity of the blends and affects notably their macroscopic behavior. These observations are interpreted as a consequence of the modification at microlevel of adherence between particles and matrix phases. The use of a nonlinear micromechanical model allows us to confirm this interpretation

Etude expérimentale et modélisation du comportement de polymères thermoplastiques renforcés : polypropylène chargé de fibres de chanvre

Ces travaux portent sur l'étude du comportement et de l'endommagement d'un thermoplastique, polypropylène, chargé de fibres courtes de chanvre. Des essais de traction à différentes vitesses de déformations (10-4 à 10-1s-1), températures (0°C à 60°C) et taux de chanvres (5% à 20%) ont été effectués. L'endommagement est observé par thermographie IR et tomographie post-mortem. Une modèle éléments finis, basé sur une caractérisation fine 3D de la microstructure du composite à partir de coupes tomographiques, approche le comportement macroscopique du composite

Macroscopic behavior of a reinforced elastomer: micromechanical modelling and validation

In the present study, we propose an evaluation of a non-linear homogenization model applied to hyperelastic composites having random microstructure. This modelling approach consists in a 3D implementation of the second order method introduced by Ponte Castañeda & Tiberio [1]. We first recall the basic principles of this method. Then, we investigate a composite made up of an hyperelastic matrix reinforced by spherical deformable or rigid particles. Computational issues of the micromechanical model are discussed and some obtained results allow to demonstrate the reinforcement effect of the particles. In order to provide a rigorous evaluation of the methodology, finite elements computations, on an unit cell, are performed and compared to the predictions of the model. Finally, a confrontation with experimental results is provided

Successful Thrombectomy Improves Functional Outcome in Tandem Occlusions with a Large Ischemic Core

International audienceBackground: Emergent stenting in tandem occlusions and mechanical thrombectomy (MT) of acute ischemic stroke related to large vessel occlusion (LVO-AIS) with a large core are tested independently. We aim to assess the impact of reperfusion with MT in patients with LVO-AIS with a large core and a tandem occlusion and to compare the safety of reperfusion between large core with tandem and nontandem occlusions in current practice. Methods: We analyzed data of all consecutive patients included in the prospective Endovascular Treatment in Ischemic Stroke Registry in France between January 2015 and March 2023 who presented with a pretreatment ASPECTS (Alberta Stroke Program Early CT Score) of 0–5 and angiographically proven tandem occlusion. The primary end point was a favorable outcome defined by a modified Rankin Scale (mRS) score of 0–3 at 90 days. Results: Among 262 included patients with a tandem occlusion and ASPECTS 0–5, 203 patients (77.5%) had a successful reperfusion (modified Thrombolysis in Cerebral Infarction grade 2b-3). Reperfused patients had a favorable shift in the overall mRS score distribution (adjusted odds ratio [aOR], 1.57 [1.22–2.03]; P < 0.001), higher rates of mRS score 0–3 (aOR, 7.03 [2.60–19.01]; P < 0.001) and mRS score 0–2 at 90 days (aOR, 3.85 [1.39–10.68]; P = 0.009) compared with nonreperfused. There was a trend between the occurrence of successful reperfusion and a decreased rate of symptomatic intracranial hemorrhage (aOR, 0.5 [0.22–1.13]; P = 0.096). Similar safety outcomes were observed after large core reperfusion in tandem and nontandem occlusions. Conclusions: Successful reperfusion was associated with a higher rate of favorable outcome in large core LVO-AIS with a tandem occlusion, with a safety profile similar to nontandem occlusion