Flat Disc Acrylic Plastic Windows for Man-Rated Hyperbaric Chambers at the USN Experimental Diving Unit

Abstract

Fl~t disc acrylic plastic windows have been designed, fabricated, evaluated and delivered to EDU for replacement of glass windows used to date. The large (D = 6.950 inches; t -1.650 inches) and the small (D o -4.450 inches, t -1.040 inches) windows have been found on the basis of an extensive evaluation program to be more than adequate for man-rated service under 450 psi maximum operational pressure in steel flanges with D (diameter of opening in flange) of 5.000 and 3.000 inches. All windows were prooftested to 675 Fsi pressure at 120OF ambient temperature prior to delivery.

Criteria for Eliminating Cyclic Limit for PVHO Flat Disc Windows

“…Fig. 5 is an example of a flat disc window that failed during pressurization 12 times its rated pressure [13]. The nonlinear FEA stresses for this test are consistent with the observed failure mode.…”

“…This window was cyclically loaded to failure at pressures ranging from 24.1-37.9 MPa (3500-5500 psi). [13] The lowest test pressure was 7.7 times the design pressure. This design provides a concrete example of cyclic failure.…”

“…The cyclic tests to failure did not have a retaining ring nor appropriate hard bearing gasket. [13] The second design was to be used for the US Navy's Experimental Diving Unit (EDU). The 112.5 mm (4.43 in.)…”

“…This sample failed in the first cycle. [13] The peak strain energy as well as peak window stress is at the corner-to-window interface indicated by the bolt.. The largest area of above-tensile PMMA is the center of the higher pressure face (circled region on the left.).…”

“…The stated intention of test was to induce failure using assumptions and conditions that would be more conducive to failure than the actual installation. [13]. Rather than redesigning the test apparatus into a fully PVHO compliant viewport assembly, the "at service pressure" model had the hard bearing and soft gasket added to the model then the soft gasket was displaced 30 percent in compression.…”