Characterization of cavitation development while tensile testing PVF2 using 3D X‐ray microtomography

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Experimental Characterization and Modeling of the Uniaxial Mechanical Behavior of Polypropylene Before Necking

Mechanical tests were performed in the pre-necking domain of polypropylene (PP) to characterize its mechanical behavior. Test results have distinctly characterized both its viscoelastic and its viscoplastic behavior. The usual approach to studying metals was adopted to investigate the effect of heterogeneities on the different features of the viscoplastic behavior of the polymer. Particular developments were necessary to adapt these methods to the semicrystalline polypropylene. By the macroscopic approach initially introduced by Cottrell, the macroscopic stress was split into an effective stress and a back stress so that the interactions between the crystalline lamellae and the amorphous phase could be taken into account. The modeling of the viscoelastoplastic behavior of PP is described by using the partition of total strain into a viscoelastic strain and a viscoplastic strain. The rheological model of Zener was used and improved with the experimental observations to model the viscoelastic behavior. As for viscoplastic behavior modeling, it's based on the characterization of the mechanical behavior in terms of effective stress and back stress associated with incompatibilities of deformation

Evolution of the Elastic Properties of an Oilwell Cement Paste at Very Early Age under Downhole Conditions: Characterization and Modelling Évolution des propriétés élastiques d’une pâte de ciment pétrolier au très jeune âge dans des conditions HP/HT : caractérisation expérimentale et modélisation

A multi-scale homogenization approach coupled with a hydration model is adopted to predict the bulk and shear moduli evolution of an oilwell cement paste at a very early age (up to one day). Calorimetric experiments were performed to be compared with the results of the kinetics model and also to study the pressure and temperature effects on the hydration kinetics. The homogenization model results are in agreement with the elastic moduli measurements obtained from propagation of ultrasonic waves. Une modélisation multi- échelle, couplée avec un modèle d’hydratation, est proposée pour prédire l’évolution des propriétés élastiques d’une pâte de ciment pétrolier au très jeune âge (jusqu’à un jour). Des résultats expérimentaux montrent que la pression appliquée (1-200 bar) pendant la prise a peu d’effet sur la cinétique d’hydratation contrairement à la température (20-60°C). Le modèle d’hydratation retenu a été validé par des mesures calorimétriques. Les résultats de porosité déduits de ce modèle d’hydratation sont d’ailleurs cohérents avec des mesures de la porosité connectée effectuées à différents degrés d’hydratation. La modélisation multi-échelle par homogénéisation prend en compte l’évolution des fractions volumiques des constituants de la pâte de ciment au cours de l’hydratation. Le développement des propriétés élastiques du ciment pétrolier au très jeune âge obtenues avec ce modèle est en bon accord avec les mesures obtenues par la propagation d’ultrasons

Mechanical behaviour of a semicrystalline polymer before necking

The behaviour of semicrystalline polypropylene (PP) was studied in the pre-necking domain. Mechanical tests were performed to characterize the behaviour of this multiphase material. Test results have distinctly characterized both its viscoelastic and its viscoplastic behaviour. The usual approach to studying metals was adopted to investigate the effect of heterogeneities caused by spherulitic morphology. By this macroscopic approach, the macroscopic stress was split into an effective stress and a back stress so that the interactions between crystalline lamellae and amorphous phases could be taken into account. This improved knowledge of the macroscopic mechanical behaviour was used to develop both viscoelastic and viscoplastic models

Physico-chemical and mechanical degradation of polyamide 11 induced by hydrolysis and thermal ageing

International audienceThis paper deals with the effect of both temperature and water activity on polyamide 11 physico-chemical and mechanical properties. The purpose of this work is to describe the ductile-brittle transition of polyamides during ageing in a wet environment using a mechanical behavior model. For that it is necessary to make physico-chemical analyzes (DSC, FTIR, GPC, viscosity) and mechanical tests (uniaxial tensile test and DMTA). These characterizations were carried out on safe and samples aged until 60 days under hydrothermal conditions in acid water, and under purely thermal conditions in a neutral environment. Changes in mechanical properties with ageing were observed in the polymer and were correlated to morphological changes deduced from the physicochemical characterizations. An increase of the second yield stress related to the recrystallization and a decrease of the strain at break due to the decrease of the molecular weight were observed during ageing

Investigation of the 3D crystalline network impact on the elastic properties of semi-crystalline polymers from a multi-scale modelling approach

International audienceNowadays, computational resources allow carrying out mechanical calculations on complex multi-scale materials. Finite Element (FE) calculations can especially be directly performed on microstructures of materials. This work is a first attempt to analyse the impact of the crystalline architecture at a mesoscopic scale on the macroscopic elastic properties of Semi-Crystalline Polymers (SCP). Such polymers can be considered biphasic materials, which are composed of an amorphous phase embedded in a crystalline network. The material studied here is Polyethylene (PE). Molecular Dynamics (MD) calculations are carried out on a 100% crystallized Polyethylene model to determine the elastic properties of the crystalline regions of the material. 3D mesostructures of the typical layout of the spherulitic crystalline network of Semi-Crystalline Polymers are then constructed from experimental observations. These material data and this geometrical description are then integrated in computations with the Finite Element method on elementary volumes to finally determine the macroscopic elastic properties of the material. In this work, which is a first attempt to test such a multi-scale workflow, no amorphous phase is considered. Different 3D architectures are compared demonstrating the role of the crystalline arrangement on the stiffness of the material. Three main types of mesostructures have been analysed: crystalline lamellae disposed in a complete random arrangement, crystalline lamellae disposed in a spherulite arrangement, crystalline lamellae with branches disposed in a spherulite arrangement. It appears that the 3D configuration of the lamellae, as well as the presence of branches, have an influence on the macroscopic elastic properties of the material. Then, comparisons with experimental data suggest that the macroscopic elastic properties can be represented with a purely cohesive crystalline network for crystalline degree up to about 50%. This result questions the role of the amorphous phase on the elastic properties of such systems