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International audience; This paper deals with the thermal effects associated with deformation processes in unfilled natural rubber. Temperature variations are measured by infrared thermography during cyclic uniaxial mechanical tests at ambient temperature. Results show that natural rubber mainly exhibits entro-pic behaviour: the material produces (resp. absorbs) heat during loading (resp. unloading). The thermal responses obtained provide complementary information regarding the mechanical analysis of changes in the microstructure, especially strain-induced crystallization. The crystallization of the polymer chains under tension leads to a temperature increase of the order of several degrees Celsius. If crystallization occurs, a hysteresis loop is observed in terms of the strain-stress relationship. Moreover, stress relaxation tests show that the thermal signatures of crystallization and of crystallite melting are different. Indeed, if the strain is maintained fixed during loading, the temperature continues to increase for a few seconds before returning to the ambient temperature. This reveals that crystallization continues during relaxation. On the contrary, if the strain is maintained fixed during unloading, the specimen seems to return instantaneously to the ambient temperature. Throughout this paper, the effect of heat exchanges with the outside of the specimen (non-adiabaticity) on the temperature variations is taken into account for the analysis.

International audience; The study deals with the experimental characterization of heat sources produced in a crack tip zone of two types of carbon black filled rubbers: a Styrene Butadiene Rubber (SBR) and a Natural Rubber (NR). For this purpose, full thermal and kinematic field measurements were performed. In NR, crystallisation increases the stiffness in the crack tip zone and consequently decreases the maximum stretch ratio. For SBR specimen, the maximum stretch ratio level at the crack tip is higher than that measured at specimen failure during homogeneous uniaxial tensile tests. During loading, the maximum temperature change is lower in NR specimen than in SBR specimen. For both materials, the heat sources in the crack tip zone remain positive during unloading. This was not observed for homogeneous tests. This phenomenon is due to the very high mechanical dissipation production, and to crystallisation at the beginning of unloading in the case of NR.

International audience; This paper deals with the calorimetric analysis of deformation processes in natural rubber. Infrared thermography is first used to measure the temperature evolution of specimens under quasi-static uniaxial loading at ambient temperature. Then the heat sources produced or absorbed by the material due to deformation processes are deduced from the temperature variations by using the heat diffusion equation. Heat sources are a more relevant quantity than temperature variations because the latter are influenced by the heat exchanges with the outside environment of the specimen. Different results are obtained from cyclic tests and relaxation tests. First, the heat source due to thermoelastic (entropic) coupling increases with the stretch ratio at constant stretch rate. Second, no mechanical dissipation (intrinsic dissipation) is detected during the material deformation. Third, strain-induced crystallization leads to significant heat production, whereas the melting of crystallites absorbs the same heat quantity with different kinetics. This difference in kinetics explains the hysteresis loop observed in terms of the strain-stress relationship. Finally, relaxation tests on unloading show that crystallite melting does not systematically occur instantaneously. can be detectable or analyzable with the abovemen-tioned techniques. For this purpose, infrared (IR) thermography seems to be an appropriate technique to detect heat sources from measured temperature variations. Indeed, IR thermography has proved over the last twenty years to be a relevant technique to provide information of importance on the deformation processes in materials such as steels, aluminium alloys and composites. Moreover, various studies previously carried out by Chrysochoos and co-workers have shown that heat sources produced by the material itself were more relevant than tem

International audience; Granular materials are defined as a collection of solid particles whose macroscopic mechanical behavior is governed by the interaction forces between the particles. Full-field experimental data on these materials remain few compared to numerical results, even though a wide literature deals with optical imaging (combined with digital image correlation) and photoelasticimetry (to measure shear stresses in particles made of birefringent materials). We applied infrared thermography to analyze two-dimensional granular media composed of cylinders and subjected to confined compression. We analyzed the calorific signature of the contact forces, especially by revealing mechanical dissipation in the interparticle friction zones. Moreover, two constitutive materials featuring entropic and isentropic elasticity were employed to compare distinct types of thermoelastic couplings. Couplings and mechanical dissipation were separately identified at two observation scales. The perspective of this work is the experimental analysis of soft granular media.

International audience; In the present paper, the thermo-mechanical characterization of a holed glass sample under cyclic loading is carried out. Due to the low thermoelastic response obtained for such a material, the thermal movie has been preliminary filtered. The experimental stress field obtained from the Thermoelastic Stress Analysis (TSA) is well correlated to the finite element model. It validates both the use of this experimental technique to study the thermoelastic response of brittle materials and the filtering methodology. Finally, the corresponding calorimetric response has been determined by using a simplified formulation of the heat diffusion equation. This permits to quantify heat sources and to carry out energy balances.

International audience; This paper proposes a noise suppression methodology to improve the spatio-temporal resolution of infrared images. The methodology is divided in two steps. The first one consists in removing the noise from the temporal signal at each pixel. In the second step, the residual offset is identified by considering thermal images for which no mechanical loading is applied. In this case, the temperature variation field is homogeneous and the value of temperature variation at each pixel is theoretically equal to zero. The method is first tested on numerical images. The results demonstrate that this approach permits to keep the spatial resolution of infrared images equal to 1 pixel. The methodology is then applied to characterize thermal activity of a defect at the surface of inorganic glass submitted to cyclic mechanical loading.

International audience; This paper investigates the thermomechanical behavior of Al-Mg alloys submitted to biaxial loading until fracture. The study aims to characterize calorimetric signature accompanying the formation and propagation of Portevin-Le Chatelier (PLC) bands induced by such a loading condition. Full kinematic and thermal fields on the specimen surface were characterized by using Digital Image Correlation (DIC) and infrared thermography (IRT). Heat source field was reconstructed from the temperature field and the heat diffusion equation. The heat source map enables us to visualize spatio-temporal gradients in the calorimetric response of the material and to investigate the kinematics of PLC bands induced by equibiaxial tensile loading. Under certain conditions, heat source maps can be seen as mechanical dissipation maps. At the specimen centre, the heat source exhibits jumps that fit with jumps of temperature and equivalent deformation rate.