Control of reactions and network structures of epoxy thermosets

International audienc

Comportement visco-hyperélastique endommageable d'élastomères SBR et PU : prévision de la durée de vie en fatigue

This work aims to develop a tool for predicting the lifespan of shoe soles called for fatigue-flexion. The first part of the work consists of characterizing the mechanical behavior of two elastomeres, a silica-filled rubber and a cellular polyurethane, in order to establish a constitutive law. Uniaxial and multiaxial tests, lead us to develop a constitutive law taking into account the nonlinear elasticity to large transformations (or hyperelasticite), viscoelasticite and damage. Two viscoelastic approaches are studied: the functional approach and the internal variable approach. The laws of behavior are then identified from the simple tests (traction and compression), and validated thanks to the multiaxial tests (tests on notched axisymmetric specimens, used for fatigue tests). On the other hand, the role of silica fillers in the behavior and damage of rubber is studied through complementary tests, and in particular by in situ-meb tensile tests. The last part of the study concerns the resistance to the initiation of a fatigue crack of the loaded rubber. A campaign of tensile-compression and torsion tests on notched axisymmetric specimens is conducted. The synthesis of the results shows two critical parameters of fatigue damage: the maximum principal deformation and the amplitude of the deformations. The observation of fracture facies highlights the zones of initiation on axisymmetric test pieces. These zones correspond either to zones of silica segregation or to a surface defect.Ce travail vise a mettre au point un outil de prevision de la duree de vie de semelles de chaussure sollicitees en fatigue-flexion. La premiere partie du travail consiste a caracteriser le comportement mecanique de deux elastomeres, un caoutchouc sbr charge de silice et un polyurethanne cellulaire, afin d'etablir une loi de comportement. Des essais uniaxiaux et multiaxiaux, nous amenent a mettre au point une loi de comportement prenant en compte l'elasticite non lineaire aux grandes transformations (ou hyperelasticite), la viscoelasticite et l'endommagement. Deux approches viscoelastiques sont etudiees : l'approche fonctionnelle et l'approche par variables internes. Les lois de comportement sont alors identifiees a partir des essais simples (traction et compression), et validees grace aux essais multiaxiaux (essais sur eprouvettes axisymetriques entaillees, utilisees pour les essais de fatigue). Par ailleurs, le role des charges de silice sur le comportement et sur l'endommagement du caoutchouc est etudie a travers des essais complementaires, et en particulier par des essais de traction in situ-meb. Le dernier volet de l'etude concerne la resistance a l'amorcage d'une fissure en fatigue du caoutchouc charge. Une campagne d'essais de traction-compression et torsion sur eprouvettes axisymetriques entaillees est menee. La synthese des resultats fait apparaitre deux parametres critiques d'endommagement en fatigue : la deformation principale maximale et l'amplitude des deformations. L'observation des facies de rupture met en evidence les zones d'amorcage sur les eprouvettes axisymetriques. Ces zones correspondent soit a des zones de segregation en silice, soit a un defaut de surface

COMPORTEMENT VISCO-HYPERELASTIQUE ENDOMMAGEABLE D'ELASTOMERES (SBR ET PU) (PREVISION DE LA DUREE DE VIE EN FATIGUE)

PARIS-MINES ParisTech (751062310) / SudocSudocFranceF

Data-enabled comparison of six prediction models for concrete shrinkage and creep

Modeling the shrinkage and creep of concrete is a demanding task due to the large number and high complexity of the parameters that contribute to these two mechanisms. A range of models have been developed to date to predict shrinkage and creep over time. Among them, this study focused on some of the most widely used models, including those developed by the American Association of State Highway and Transportation Officials, the American Concrete Institute, the European Committee for Standardization, the Fédération Internationale du Béton, and the Comité Européen du Béton. This holistic investigation aimed to provide in-depth insights into the input requirements and prediction capabilities of the identified models. For this purpose, using various data sets selected from the NU-ITI database, the performance of each shrinkage and creep model was first assessed, and a calibration approach was then employed to further refine their outputs. The calibration was performed with the objective of adjusting the short- and long-term prediction accuracy, including the rate of shrinkage and creep development over time. The models were evaluated side by side through comparing the outputs of each calibrated model to data from shrinkage and creep experiments. The calibration steps explored in this study were found to improve the performance of the shrinkage and creep prediction models by up to 20%. This helped reduce the possibility to deviate from the expected strains and stresses. The outcome of this detailed study paved the way to properly select and utilize shrinkage and creep models, taking into consideration the key contributing factors for the highest accuracy

Novel reactive elastomer-metal oxide composite: Effect of filler size and content on swelling and reinforcement

A novel elastomer-metal oxide composite that swells and stiffens upon hydration will be presented. Conventional water-swellable elastomers filled with hydrogels absorb water and swell upon hydration but their modulus decreases as a result of fluid water diluting the rubber matrix. Reduced stiffness compromise the reliability of swellable elastomers used in sealing applications. One major application of swellable elastomers is fluid containment seals for zonal isolation in the oilfield. For effective sealing, the contact pressure between the seal and the surrounding wall should be high while deformation should be limited when a differential pressure is applied. Both conditions can be achieved by means of swelling and stiffening of the seal; hence, the new reactive elastomer-metal oxide composite is developed such that after it is exposed to water, the composite swells and stiffens simultaneously. Composites filled with different amounts of oxide were studied and it was observed that swelling up to almost 100% with an increase in modulus of about 200% could be achieved for the best performing compound. Composites filled with different sizes of the metal oxide were also studied. The finest filler was found to impart the greatest modulus, both before and after hydration, to the composite although swelling was slightly reduced compared with the larger particles. Another advantage of the composite for sealing purposes is that the swelling is largely retained even after complete removal of the solvent; i.e., drying.Published versio

Swellable elastomeric HNBR-MgO composite : magnesium oxide as a novel swelling and reinforcement filler

In this paper, we introduce a novel reactive rubber composite made by compounding magnesium oxide (MgO) powder with hydrogenated nitrile butadiene rubber (HNBR). This HNBR-MgO composite system initially looks and behaves like rubber, but exposure to water causes it to swell and stiffen. Compared with conventional swellable materials, which lose stiffness significantly upon swelling, the sealing capacity of these novel reactive composites improves significantly with their improved stiffness. Three mixing ratios of HNBR and MgO were examined in this study, and their properties upon reaching equilibrium in water of 82°C were reported. The elastic modulus value tripled, reaching 80 MPa, while doubling in volume for the rubber filled with 40% by volume of MgO. After drying, modulus of this particular composite increased even further to almost 200 MPa while the volume expansion was largely retained (shrinkage of approximately 10%). In this paper, we will show that the increase in elastic modulus and volume increase are related to the reaction of MgO with water to form magnesium hydroxide, absorbing water molecules into the composite and chemically reacting with it in the process.Accepted versio

Influence of defect orientation on electrical insulating properties of plasma-sprayed alumina coatings

International audienceThe influence of the microstructure (pores and cracks) on electric properties of plasma-sprayed alumina coatings was investigated using the so-called Scanning Electron Microscope Mirror Effect (SEMME) technique. Coatings were sprayed with different alumina feedstock powders on various atmospheres using a CAPS (‘Controlled Atmosphere Plasma Spraying'). Microstructures with various amount of porosity and cracks orientation distributions were analysed. Both outer surfaces and cross-sections of alumina coatings have been analysed by SEMME technique using two complementary modes (measurement of absorbed current and mirror methods). Originally developed to study the behaviour of injected electrons and related phenomena, such as trapping ability, detrapping process and relaxation phenomena in bulk insulating materials, the SEMME technique was successfully applied, in this study, to porous coatings. It is proved that cracks orientation modifies both motion and trapping of charges and therefore the dielectric properties of plasma-sprayed alumina coatings

Study of the influence of microstructure on electric properties of plasma-sprayed aluminia coatings using the scanning electron microscope mirror effect (SEMME) method

International audienc

Study of the porosity in plasma-sprayed alumina through an innovative 3-dimensional simulation of the coating build-up

International audienc

Stimuli-Responsive Cement-Reinforced Rubber

In this work, we report the successful development of a cement–rubber reactive composite with reversible mechanical properties. Initially, the composite behaves like rubber containing inert filler, but when exposed to water, it increases in volume and reaches a stiffness that is intermediate between that of hydrogenated nitrile butadiene rubber (HNBR) and hydrated cement, while maintaining a relatively large ductility characteristic of rubber. After drying, the modulus increases even further up to 400 MPa. Wet/drying cycles prove that the elastic modulus can reversibly change between 150 and 400 MPa. Utilizing attenuated total reflection Fourier transform infrared spectroscopy), we demonstrate that the high pH produced by the hydration of cement triggers the hydrolysis of the rubber nitrile groups into carboxylate anions. Thus, the salt bridges, generated between the carboxylate anions of the elastomer and the cations of the filler, are responsible for the reversible variations in volume and elastic modulus of the composite as a consequence of environmental moisture exposure. These results reveal that cement nanoparticles can successfully be used to accomplish a twofold task: (a) achieve an original postpolymerization modification that allows one to work with carboxylate HNBR (HXNBR) not obtained by direct copolymerization of carboxylate monomers with butadiene, and (b) synthesize a stimuli-responsive polymeric composite. This new type of material, having an ideal behavior for sealing application, could be used as an alternative to cement for oil field zonal isolation applications