INTRODUCTION 



The Naval Facilities Engineering Command Is responsible for the construction 

 and maintenance of underwater structures attached to the ocean floor. Such struc- 

 tures may include instrumented or manned underwater surveillance or observation 

 posts that will rely (at least In part) on visual observation and the transmission and 

 reception of electromagnetic radiation through nonopaque areas of the hull for the 

 performance of their mission. The Deep Ocean Laboratory of the Naval Civil 

 Engineering Laboratory (NCEL) Is carrying out studies to provide information on the 

 design of underwater windows. The first report^ on these studies discussed the behav- 

 ior of conical acrylic windows under short-term pressurlzatlon. The report In hand 

 presents information on the behavior of flat, disk -shaped acrylic windows under 

 short-term pressurlzatlon. 



Flat, disk-shaped acrylic windows for high-hydrostatlc-pressure applications 

 have received very limited attention, and only a few facets of their behavior under 

 hydrostatic loading have been investigated. 2 Since flat windows possess characteris- 

 tics not inherent In conical acrylic windows currently In use in underwater structures. 

 It was considered desirable to investigate this type of window. 



The major advantage of flat windows Is the commercial availability of glass, 

 acrylic, epoxy, and polycarbonate material in polished transparent sheets or plates. 

 Conical windows require considerable precision machining to adapt flat sheets or plates 

 to the window flange. On the other hand, flat windows require only simple cutting 

 and turning to transform flat material into usable windows. Furthermore, the fabri- 

 cation of the flat-window mounting flange Is also much simpler. Since the mating 

 surfaces of both the window and flange are plane, the problem of replacement of 

 windows Is simplified when they become defective due to mechanical damage or the 

 cracking which precedes failure under pressure. There may, of course, be some 

 disadvantages associated with flat windows, such as smaller angle of vision for the 

 same flange opening, but there are sufficient advantages inherent in flat windows to 

 make them worthy of investigation for underwater structural applications. 



The underwater structures in which flat windows could be Incorporated may be 

 subjected to a variety of hydrostatic loadings. Thus a series of studies must be con- 

 ducted to determine their behavior under short-term, long-term, cyclic, and dynamic 

 loading. The first of the studies conducted deals with the short-term hydrostatic 

 loading of flat acrylic windows, where short-term hydrostatic loading Is defined as 

 pressurizing the window on its high-pressure face at a 650-psl/mIn rate from zero 

 (atmospheric) pressure to its failure pressure. The purpose of this report Is to document 

 the first experimental study. 



