VISCOELASTICITY AND DYNAMIC FATIGUE CRACK GROWTH BEHAVIOR OF NATURAL RUBBER/CIS-POLYBUTADIENE RUBBER COMPOSITES

Because cis-polybutadiene rubber (BR) can improve the fatigue crack growth (FCG) resistance of natural rubber (NR) in the low-tearing-energy (G) range, a blending system of NR/BR is often used in tire materials. In this study, based on relationship of (FCG rate (dc/dN)-G) established from the perspective of fracture mechanics and then inspired by Persson's theory and starting from the perspective of viscoelasticity, the FCG behavior and mechanism of NR/BR were investigated. NR/BR with different blending ratios were prepared, and dc/dN under different G inputs (500/1500 J/m(2)) was measured. According to the viscoelastic parameters (storage modulus E', loss factor tan delta, and loss compliance modulus J '') recorded in situ, energy dissipation distribution at the crack tip (energy consumption for FCG inside crack tip: G(0) and energy loss in linear viscoelastic zone near crack tip: G(0) f [v,T]) was determined, and the relationship of (viscoelasticity - dc/dN) was finally set up. When G=500 J/m(2), blending BR can reduce dc/dN as compared with pure NR. On one hand, with a higher BR fraction, an increased cross-linking density and enhanced filler network provided greater rigidity, which increased E'; on the other hand, a low glass transition temperature and flexible chain of BR reduced hysteresis, which decreased tan delta. The joint action led to a decrease in J '', which caused more G(0) f (v, T) and less G(0), resulting in the ultimate reduction of dc/dN. In contrast, for G = 1500 J/m(2), when the BR content was >50 phr, dc/dN showed a significant increase. Although more BR evidently decreased J '' and then led to a large amount of G(0) f (v, T), due to absence of strain-induced crystallization, the chain orientation of BR was hard to resist FCG when G increased. Finally, the morphology of the crack tip propagation path was captured to corroborate the different orientation characteristics of NR and BR and their effects on FCG behavior.