Thermomechanical and calorimetric characterization of crack tip zones under large heterogeneous deformations, Part II: Full strain, calorimetric and strain-induced crystallinity fields at the crack tip of an unfilled natural rubber

In the first part of this paper, a methodology has been developed for tracking moving material points within infrared images, by coupling full kinematic and thermal field measurements. The kinematic field is determined with the Digital Image Correlation (DIC) technique and the temperature field is measured with an infrared (IR) camera. This methodology enables us to provide simultaneously the strain field, the thermal field, the heat power density (the heat source) field and, if applicable, the crystallinity field under large heterogeneous deformations. Its metrological performances have been fully characterized. The technique is the only one providing all these results from the same test, which avoids bias due to the repetition of the test with different specimens, different testing machines and differences in the boundary conditions applied. In this second part, the methodology is applied to a stretched crack tip in an unfilled natural rubber specimen. The crack tip is observed after several hundred of mechanical cycles applied to the notched specimen. The quantitative analysis of the different fields and profiles plotted (along the crack lips and behind the crack tip) enables us to characterize and to compare the different gradients in terms of strain, temperature, heat source and crystallinity. Quantitative analysis of the results supports the assumption that under the conditions of the experiment, the crack tip is the most stretched zone but not the most crystallized one, compared to the zones on both sides of it. The results also suggest that cavitation and/or decohesion might locally occur at the crack tip and frustrate the crystallization. • Full kinematics, thermal and calorimetric fields are mapped at the crack tip of a NR. • The crack tip is observed after several hundred of mechanical cycles. • A quantitative analysis is performed from profiles along the crack and in depth. • The crack tip is the most stretched zone but not the most crystallized one. • Cavitation and/or decohesion might occur and frustrate SIC at the crack tip.