Flanged Acrylic Plastic Hemispherical Shells for Undersea Systems. Static and Cyclic Fatigue Life under Hydrostatic Loading.

摘要

Twenty-four acrylic plastic windows in the shape of hemispherical domes with equatorial flanges have been thermoformed from flat sheets and tested under short-term, long-term, and cyclic pressure loading at 65 to 75 F (18.5 to 24.1 C) ambient temperature. Two kinds of flanges were studied: Type I, a flat lip with a rounded heel and instep, and Type VI, a conical lip with a rounded heel. The 14,500-psi, short-term critical pressure for hemispherical windows with t/Ri=0.364 was found to be independent of the equatorial flange configuration. Both the static and cyclic fatigue lives of the windows were also found to be independent of equatorial flange configuration. In either case, the maximum acceptable working pressure for 65 to 75 F temperature range was found to be 1,000 psi. Only by elimination of the O-ring groove in the bearing surface of the window flange and the use of a thin neoprene bearing gasket between the acrylic flange and the steel seat is it possible to extend the working pressure for 65 to 75 F (18.5 to 24.1 C) temperature range to 2,000 psi. Operating the flanged windows at pressures in excess of the safe working pressures shown above will generate fatigue cracks in the bearing surface of the flange in less than 1,000 pressure cycles; at 5,000-psi pressure the cyclic fatigue life decreases to less than 100 cycles. (Author)