Experimental characterization of the fracture behavior of soft rubbers

Abstract

Rubbers are frequently used in various engineering applications, such as pneumatic tires, vibration isolators, sealants, and transmission belts. In these applications, rubber materials need to endure various mechanical loading conditions and resist fracture. The mechanical properties (e.g., modulus and toughness) and service life of rubbers can be improved by incorporating fillers (e.g., carbon black or silica) in the rubber matrix. However, filled rubbers exhibit stress-softening phenomenon known as the Mullins effect when first stretched. Therefore, during the deformation of filled rubbers, a large amount of the strain energy can be dissipated, leading to enhanced crack resistance. A better understanding of the energy dissipation that occurs during crack propagation is important for the predictive modeling of the fracture process. This report describes a set of experimental studies on the energy dissipation caused by Mullins softening during crack propagation in rubbers. A particle tracking method is used to measure the nonlinear local strain fields observed when notched rubber specimens are subjected to tensile loading. Using the measured deformation fields, we quantitatively estimate the dissipative and intrinsic fracture toughness during steady state crack propagation in filled and unfilled rubbers subjected to monotonic loading. We then present a study investigating the effect of global loading rate on the fracture toughness of filled rubber subjected to relatively high monotonic loading rates. Our observations indicate that the crack propagation velocity influences the intrinsic fracture toughness. The last part focuses on analyzing crack growth behavior in filled rubber subjected to high-strain amplitude cyclic loading. We closely monitor the evolving softening phenomena, particularly the region surrounding the crack tip, on the surfaces of pure shear specimens. Our observations revealed a correlation between the proximity of material points to the crack path and the extent of deformation. Additionally, we observed variations in deformation during both loading and unloading phases at specific material points.