Thermomechanical and calorimetric characterization of crack tip zones under large heterogeneous deformations, Part I: A method coupling full kinematic and thermal fields for high resolution surface micro-calorimetry

The thermomechanical and calorimetric responses accompanying the deformation of materials bring complementary information to purely mechanical approaches. In the case of elastomers, many studies carried out under homogeneous strain fields are available in the recent literature. They enable us to discuss the nature of the elasticity (due entropic and/or isentropic couplings), to identify the intrinsic dissipation (due to viscosity and/or damage) and to determine whether or not the material experiences microstructure changes. In the case large heterogeneous strain fields, typically those induced in the vicinity of a crack tip, imaging systems must be coupled in order to track the points that are moving the IR images. The first part of the present article deals with the development of a methodology for reconstructing heat source surface fields in the case of large heterogeneous deformations. This methodology is based on the coupling of full kinematic and thermal fields measurements, for compensating the point motion in the thermal images in order to calculate the heat source from the heat diffusion equation. A complete metrological characterization has been carried out. It shows that the compensation technique does not alter significantly the thermal resolution in the variation range of experimental parameters in relation with the experimental setup used. The heat source resolution reached is less than 5 1 0 3 W/m 3 , which is two orders of magnitude less than the heat source values classically measured for stretched elastomers. The accuracy of the conduction term has been evaluated in the Lagrangian configuration according to the temperature gradient level. This methodology is used in the second part of the present paper to characterize full strain, calorimetric and strain-induced crystallinity fields at the crack tip of a natural rubber submitted to cyclic loadings. • A methodology for reconstructing heat source surface fields have been developed. • It is dedicated to the case of large heterogeneous deformations. • It is based on the coupling of full kinematic and thermal fields measurements. • The conduction term has been evaluated in the Lagrangian configuration. • A complete metrological characterization has been carried out.