Identification of failure mechanism consistency for NBR accelerated test

A consistent failure mechanism is a precondition for accelerated tests, and the accurate identification of the catastrophe point at which the failure mechanism transforms remains a longstanding challenge in accelerated tests. In this study, an independently designed test apparatus was adopted to monitor the variation in the compressive stress of nitrile butadiene rubber (NBR) samples at different temperatures. The deformation of the samples was controlled as a constant so the variation of the stress could be correlated with the mechanical properties of the NBR. In addition, thermal analysis and infrared spectroscopic analysis were conducted for NBR samples without applying external stresses (e.g., free state) at various elevated temperatures. Samples stored at room temperature for two years were also tested and analyzed to provide a baseline. The results indicate that the stress relaxation mechanism for NBR aged at 80 °C differs from that for samples aged at 90 °C. The dominating aging mechanism for NBR samples stored at room temperature and accelerated at 80 °C is free radical oxidation. The main mechanism under 90 °C was found to be chain scission. After combining the changes in macroperformance and microstructure, we concluded that the change in aging mechanism occurred between 80 °C and 90 °C.