Report on Incidental Findings of Cyclic O-Ring Behavior During Fuel/Elastomer Compatibility Testing

Abstract During a recent investigation into elastomer O-ring compatibility with conventional and sustainable jet fuels, a cyclical swelling behavior was identified that cannot be fully accounted for with normal swelling reactions attributed to the aromatic content of the tested fuel. The data showed a 24-hour cycle corresponding to daily solar cycles with increased swelling during hours of unobstructed daylight then decreasing after sunset. These cycles were present regardless of the O-ring interaction with fuels. The rate of O-ring swell increase was seen to begin at sunrise reaching a peak when the amount of solar radiation was greatest. The severity of the swell would decrease or cease entirely as the UV index increased. A thorough literature review, conducted to identify similar trends, revealed 24-hour cycles with little examination beyond assumptions of laboratory temperature fluctuations causing the swell. Although ambient temperature has been shown to influence O-ring swell, the air conditioning cycles are much shorter and do not necessarily explain a continuous swelling rate increase over a 12-hour period. A preliminary experiment was conducted to determine the influence of UV exposure to O-ring swell indicating an O-ring reaction by the evidence of swell. The motivation of this work is based on the gap of knowledge in literature about these common trends with a goal to introduce O-ring cyclic behavior formally. Additionally, this paper will discuss the potential UV mechanism influencing the 24-hour cycle O-ring swell with preliminary data.