Effect of constrained strain on failure behavior of rubber vulcanizates

Abstract

In diesel engine fuel system, the rubber components such as gaskets and hoses are usually made of nitrile rubber. In such application, the rubber components are exposed to aggressive solvent, i.e. diesel fuel. While the compatibility of elastomers in the conventional diesel has long been established, their compatibility in biodiesel remains incompletely understood. Indeed, the intense study on biodiesel as alternative source of energy has increased tremendously since the existing fossil fuels are no longer considered as feasible due to their ever increasing cost, their continuous diminution in supply and environmental concerns. Furthermore, the abundant feedstock of biodiesel such as palm biodiesel in Southeast Asia along with the existing tropical climate has favoured further research works in this field. During the service, rubber components are usually subjected to cyclic loading for a long term duration (fatigue loading). From the standpoint of replacing conventional diesel with biodiesel, it is necessary to study and to compare the fatigue performance of rubber exposed to biodiesel and conventional diesel. The present study investigates the fatigue damage in swollen nitrile rubber due to exposure to biodiesel and conventional diesel. Swollen nitrile rubber specimens are obtained through stress-free immersion tests in palm biodiesel (B100) and conventional diesel fuel (B0) to attain the same degree of swelling. The uniaxial fatigue tests are subsequently conducted on both dry and swollen rubbers. Field Emission Scanning Electron Microscopy (FESEM) analysis is carried out to observe the fracture surfaces. Stretch-N curves are plotted to illustrate the fatigue life duration. It is found that the swollen B100 rubber has a shorter lifetime than the swollen B0 rubber. FESEM micrographs revealed that the loading conditions have no effect on the crack initiation and propagation patterns regardless of the swelling state.