Experimental and Analytical Investigations of Crack Removal Phenomenon in Highly Deformable Rubbers Weakened by a Crack and Loaded in Mode-I Conditions

A physical phenomenon called "crack removal" is investigated for highly deformable rubbery materials containing a pre-existing crack under uniaxial pure mode-I loading. In this case, the stress concentration significantly diminishes and in a specific stage of loading, the specimen behaves as a sample which has no apparent effect from the initial sharp crack and thus nearly undergoes uniaxial state of stress until its final rupture. To explore this phenomenon that has not been previously explored, theoretical and experimental investigations were carried out in the current study. In the experimental part, due to the lack of pertinent experimental data for crack removal phenomenon, a series of mode-I fracture tests were carried out on nitrile butadiene rubber (NBR) containing 15 phr carbon black. In the theoretical part, an energy-based criterion was proposed for detecting the crack removal load and subsequently, for predicting the final rupture load in such materials. For implementation of this criterion, non-linear finite element analyses were performed. The results confirm very good ability of the proposed criterion for predicting the crack removal and final rupture phases in rubber-like materials having high deformability.