The investigation of effects of environmental conditions on fatigue strength and spring stiffness of rubber materials

Abstract

Rubber materials are widely used in many applications. The most important applications of rubber materials are seals, tires, gaskets, hoses, hydraulic-pneumatic systems and vibration absorbers. Today, the working environment of rubbers varies. It has become important to see the responses of developed rubber materials to these challenging working conditions. Most rubber parts are subjected to fluctuating loads that can cause fatigue damage in their work environments. In this study, fatigue strength and spring stiffness of rubber materials under different environmental conditions is investigated. Three general factors that affect fatigue strength of rubber materials are the effects of mechanical loading, environmental effects and the effects of rubber formulation. In this study these factors are examined. For this purpose, fatigue strength and spring stiffness of natural rubber (NR), specially developed natural rubber (S-NR) and ethylene propylene diene monomer (EPDM) rubber were examined. The fatigue tests of rubber samples were performed before and after aging processes. During the study, the static and dynamic stiffness values of the rubber materials were examined before and after aging processes. As a result of experimental study, it was found that fatigue life decreases as a result of accelerated aging and annealing in heated oil processes for NR, EPDM and S-NR samples. Annealing in heated oil process is more effective in reducing fatigue life of rubber samples compared to accelerated aging. In this study, it is seen that S-NR rubber has the highest fatigue strength among rubber materials tested. It has been determined that production of samples with the semi-active vulcanization system is the most important parameter in increasing fatigue strength. In S-NR samples produced with the semi-active vulcanization system, the loss in spring stiffness occurring under different aging conditions is less compared to the loss in spring stiffness in conventional vulcanization system produced NR and EPDM samples.