1990-07-01

Fatigue Testing of Corrugated and Teflon Hoses 901436

With the use of single and two-phase heat transport systems for the thermal control of large space facilities, there will be numerous instances where fluid lines will have to traverse joints that either rotate or move in some other manner. Flexible hoses are being considered as one means of traversing these joints. They would be subjected to a variety of stresses and to as many as 150,000 rotational cycles. In order to test the resilience of flexible hoses to bending stress, a test assembly was constructed to determine the number of flexing cycles the hoses could withstand before losing their ability to maintain a constant pressure. Corrugated metal hoses of 1/4, 3/8, and 1/2-inch diameter and teflon hoses of 3/8 (smooth bore) and 1/2-inch (convoluted) diameter were tested at different pressures with nitrogen gas. The metal hoses had lives ranging from 30,000 to 100,000 flexing cycles. But, even after 400,000 cycles, the teflon hoses remained essentially intact, though there may have been some leakage in the convoluted teflon.
Thermal control of large space facilities, such as the Space Station, will require the transport of large quantities of one or two-phase fluid over considerable distances and through a variety of fittings. In the case of actively cooled attached payloads, this transport may have to occur across joints that rotate or move in some manner. In addition, if the payload is tracking a celestial or terrestrial object, the joint could be in constant motion over the life of the space facility. This would place a tremendous strain on the fluid connection, requiring upwards of 150,000 cycles over a 10 year period with working fluids, such as anhydrous ammonia, on the inside and a space environment on the outside. One possible solution for making this type of fluid connection is to use flexible hoses. The purpose of this study was to determine by means of testing whether flexible hoses, either teflon or corrugated metal, were capable of withstanding the large number of flexes that would be experienced on a long-term space facility.

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