A study on the material properties and fatigue life of natural rubber with different carbon blacks

Natural rubber compounds filled with N330, N650 or N990 were experimentally investigated in order to examine the effects of carbon black on the fatigue life, the hysteresis, the fracture surface morphology and the critical J-value. The fatigue life was obtained by conducting a displacement-controlled fatigue test on an hourglass-shaped specimen, and the hysteresis was calculated from the loading and unloading curves obtained during the fatigue test. The fracture surface obtained after the fracture test was examined by a microscope, and its roughness was calculated for the surface profile obtained by using a stylus-type roughness tester. In addition, the critical J-value was obtained by conducting a tensile test for pre-cracked dumbbell specimens. Based on the test data, it was noticed that the fatigue life, the hysteresis, the small-scale roughness and the critical J-value were ranked in the following order for the NR compound filled with N330, N990 or N650. It was also noticed that the logarithmic value of the fatigue life was linearly proportional to the square root of the product of the critical J-value and the hysteresis.