Some specific features and consequences of the thermal response of rubber under cyclic mechanical loading

International audienceThe present paper deals with the specificities of the thermal response of rubber under cyclic mechanical loading at constant ambient temperature. This question is important, since the stabilized thermal response is used in fatigue life criteria, especially for the fast evaluation of fatigue life. For this purpose, entropic coupling in a thermo-hyperelastic framework is first used to predict the variation in the heat source produced or absorbed by the material during cyclic loading. The heat diffusion equation is then used to deduce temperature variations under adiabatic and non-adiabatic conditions. The influence of several parameters on the stabilized thermal response is studied: signal shape, frequency, minimum and maximum stretch levels, multiaxiality of the mechanical state. The results show that, in the steady-state regime, the mean value between the maximum and minimum temperature variations over a mechanical cycle is different from zero. This is due to the specific variation in the heat source, which depends on both the stretch rate and the stretch level. This result has numerous consequences, in particular for fatigue. Indeed, the stabilized mean value between the maximum and minimum temperature variations during fatigue tests does not reflect only fatigue damage, since the entropic coupling also leads to a value different from zero. This is a major difference with respect to materials exhibiting only isentropic coupling, such as metallic materials

Mechanical characterization of rubber from one heterogeneous test

International audienceThe present study deals with the mechanical characterization of elastomeric materials. Classically, three homogeneous tests are considered to identify constitutive parameters, namely Uniaxial Tensile (UT), Pure Shear (PS) and Equibiaxial Tensile (ET) tests. Here, a new method is proposed: it consists in inducing the three previous homogeneous tests from only one heterogeneous mechanical test. For this purpose, a conventional tensile machine is used and a new apparatus is designed to be adapted on the machine. The test-induced heterogeneity is discussed related to two criteria based on the existence of UT, PS and ET and on the distribution of the maximal principal elongation at each material points of the sample surface. Experimentally, kinematic fields are provided on the sample surface by an image correlation code suitable for large deformations. Finally, an inverse technique, so-called Virtual Field Method, is used to identify the material parameters in the framework of the Mooney hyperelasticity

Hyperelasticity with volumetric damage

International audienceThe present paper presents a simple framework to model continuous volumetric damage in elastomers. The formulation predicts phenomenologically the growth of microscopic cavities, and can be applied to both static and fatigue loading conditions. This first version of the approach cannot handle cavitation and is limited to small values of porosities. The derivation is based on the use of a simple scalar damage parameter, the irreversible volume change, and takes naturally into account the change in stiffness through the explicit dependence of the material parameters on the damage variable. The thermo-dynamic force which drives the volume change contains the hydrostatic stress and also a contribution due to stiffness evolution. As a first application, a damage compressible neo-Hookean constitutive equation is derived and a simple example is studied

Experimental Analysis of Prepreg Tack

International audienceA probe tack test apparatus is designed to characterize the tack of carbon-epoxy prepreg. Tests are performed on both pure resin and prepreg. The maximum debonding force seems to be a relevant measure of tack. First, results show that the response of pure resin is similar to that of viscous silicon oil. Second, the shape of the response curve obtained for prepreg beyond the maximum value of the debonding force is mainly due to structural effects. Third, the influence of contact force, contact time, debonding rate, probe temperature and ageing conditions on the prepreg tack is investigated in relation with physical phenomena involved in the debonding phase

Variabilité inter-et intraspécifique de la composition chimique de la phase minérale des ciments utilisés dans la construction du tube de plusieurs polychètes bioconstructeurs

International audienceSeveral species of marine polychaetes reside in individual protective tubes. These tubes may be agglomerated in patches of varied sizes with very high densities, or form massive reef-like mounds which can be stretch over several kilometers. These polychaetes can thus be considered as the most important building organisms after corals in coastal environments. We especially focused on several species belonging to the families of Sabellariidae, Terrebeliidae and Pectinariidae. Tubes grains are glued together with biomineralized cement secreted from a building organ connected to specialized glands. Different methods of micro-analysis were used to analyze the biomineral components of these cements for four varyingly gregarious tube-building polychaetes: Lanice conchilega, Pectinaria koreni, Sabellaria alveolata and Phragmatopoma caudata. The aim of this study is to describe and compare the inter- and the intraspecific variability in the main biomineral components of cement at local, regional and continental scales. Scanning Electron Microscopy confirms an identical structure of the cement within species of Sabellariidae in Europe and America. Electron Probe Micro-Analysis (EPMA) confirms the presence of calcium, phosphorus, and magnesium plus traces of manganese in all cements, with varying concentrations of these elements at different locations for the same species or for different species at the same location. Finally, our dataset is compared with previous studies from literature

Effect of thermal cycles on the deformation state at the crack tip of crystallizable natural rubber

International audienceThis paper deals with the effect of temperature variations on crack tip kinematicsin rubbers, especially in crystallizing rubbers. In such materials, the high deformation levelencountered at the crack tip engenders the formation of crystallites. As a consequence, thecrack tip is reinforced and resists crack growth. However, this phenomenon is signicantly affectedby variations in material temperature. This is classically observed at the macroscopicscale in terms of crack propagation rate and path. In this study, the effect of temperature isstudied at the local scale, by measuring the change in the kinematic eld at the crack tip duringthermal cycles. Results show that, in crystallizable natural rubber, the effect of temperaturedepends on the stretch ratio atained in the zone under consideration. In slightly stretchedzones, the stretch ratio increases with the increase in temperature, whereas it decreases inhighly stretched zones. This highlights the competition between the effects of the variationsin internal energy and in entropy on the thermomechanical response. Moreover, if crystallitesform in highly stretched zones, the increase in temperature leads to crystallite melting,which increases the stretch ratio. This is explained by the fact that crystallites act as llers byconcentrating the stress and therefore by increasing the apparent stiffness of the material

Hyperelasticity with volumetric damage

International audienceThe present paper presents a simple framework to model continuous volumetric damage in elastomers. The formulation predicts phenomenologically the growth of microscopic cavities, and can be applied to both static and fatigue loading conditions. This first version of the approach cannot handle cavitation and is limited to small values of porosities. The derivation is based on the use of a simple scalar damage parameter, the irreversible volume change, and takes naturally into account the change in stiffness through the explicit dependence of the material parameters on the damage variable. The thermo-dynamic force which drives the volume change contains the hydrostatic stress and also a contribution due to stiffness evolution. As a first application, a damage compressible neo-Hookean constitutive equation is derived and a simple example is studied

Etude de l'interface NiTi/silicone

National audienceLa présente étude vise à élaborer et caractériser mécaniquement un composite architecturé, constitué de Nickel-Titane (NiTi) et de silicone. Afin de pouvoir envisager l'utilisation d'un tel composite, une bonne adhésion à l'interface entre ces deux matériaux doit être assurée. L'interface entre Nickel-Titane (NiTi) et polymères a été le sujet de nombreuses études récentes. Concernant plus particulièrement les élastomères, utilisés dans le cadre de la présente application, les études sont bien plus rares. Ce travail a donc consisté à étudier l'interface entre fil de NiTi et deux silicones chargés, l'un étant biocompatible. Plusieurs méthodes d'amélioration de l'interface entre ces deux matériaux ont été testées : une désoxydation des fils, un primaire favorisant l'adhésion, et un traitement plasma. Des essais de pull-out ont été réalisés pour déterminer l'influence de ces différentes méthodes. Les résultats ont montré qu'une forte amélioration de l'adhésion était obtenue en utilisant un primaire, un traitement plasma ou encore une combinaison de ces deux traitements 1 . Dans le cadre d'applications biomédicales, une attention particulière a été portée à l'étude des paramètres du traitement plasma. Une structure composée d'un tube tricoté de NiTi enrobé de silicone a ensuite été élaborée 2 à l'aide d'un traitement plasma par argon. Des essais de traction et gonflement ont été réalisés sur ce composite architecturé

Effects of temperature on the mechanical behavior of filled and unfilled silicone rubbers

International audienceIn this contribution, the influence of the temperature on the mechanical behavior of a filled and an unfilled silicone rubber was analyzed. Firstly, the crystallization and melting temperatures were determined by differential scanning calorimetry. Secondly, mechanical tests were carried out at different temperatures above that of crystallization, up to 150°C. Results show that both silicone rubbers exhibit an entropic behavior in this temperature range. Thirdly, the temperature influence on the stress softening and mechanical hysteresis is studied and analyzed

Effects of temperature on the mechanical behavior of filled and unfilled silicone rubbers

International audienceIn this contribution, the influence of the temperature on the mechanical behavior of a filled and an unfilled silicone rubber was analyzed. Firstly, the crystallization and melting temperatures were determined by differential scanning calorimetry. Secondly, mechanical tests were carried out at different temperatures above that of crystallization, up to 150°C. Results show that both silicone rubbers exhibit an entropic behavior in this temperature range. Thirdly, the temperature influence on the stress softening and mechanical hysteresis is studied and analyzed