Heat and strain measurements at the crack tip of filled rubber under cyclic loadings using full-field techniques

This study aims at characterizing heat sources during the deformation of the crack tip zone in carbon black filled Styrene Butadiene Rubber (SBR). For this purpose, the thermomechanical response of cracked specimens was investigated using coupled full thermal and kinematic field measurements and a suitable motion compensation technique. The kinematic analysis enabled us to define the zone of influence of the crack and to measure the maximum stretch ratio level. The maximum stretch ratio level at the crack tip is higher than that measured at specimen failure during uniaxial tensile tests, which can be explained by considering the maximum chain extensibility. The calorimetric analysis shows that the high heat source gradient zone is very much more confined than the high temperature gradient zone. The heat sources at the crack tip remain positive and small during unloading, which indicates that mechanical dissipation is high and confined to the crack tip. This result highlights that the material behaves very differently in the crack tip zone compared to homogeneous tests. This proves that it not possible to predict the behavior of the crack tip zone from homogeneous tests. Moreover, it is observed that the mechanical dissipation decreases with the number of first cycles, which highlights the fact that the material is increasingly accommodated. This study provides the first accurate measurement of heat sources at the crack tip of rubber, constituting a new experimental tool in the fracture mechanics of rubber. (C) 2014 Elsevier Ltd. All rights reserved.