Agenda Session

Acrylic windows have been used in pressure vessels for human occupancy (PVHOs) since the 1950s and were incorporated into pressure vessel technology in the 1970s through the ASME standard PVHO-1, Safety Standard for Pressure Vessels for Human Occupancy.  Recently, Section VIII of the ASME Pressure Vessel Code incorporated the use of acrylic cylinders for non-PVHO pressure vessels through Appendix 48.  The established ASME PVHO-1 acrylic design method is empirically derived and is not based on direct calculations using thin-wall pressure vessel theory.  This currently precludes design by analysis (DBA) techniques.  An ASME codes & standards task group is developing a method for design by analysis for glassy polymers with the intent to extend the potential range of polymers as pressure-retaining structures, such as variations of acrylics and polycarbonates. One of the established structures is a conical frustrum, used in high-pressure boundary conditions.  This geometry typically has localized plastic strain at design conditions.  These same locations are also known crack initiation points for catastrophic failure.  This paper illustrates a method developed to model the conical frustrum in a cyclic manner using implicit nonlinear Finite Element Analysis to determine the residual strains and assess whether those strains are consistent with reliable operations or failure.   The work is based on the experiments conducted by Dr. Jerry Stachiw in developing the basis for ASME PVHO-1 and is applied to the non-compliant window design used by OceanGate in the TITAN submersible.  Going forward, the DBA techniques will extend beyond PVHOs to traditional pressure vessels, spacecraft, uncrewed systems requiring transparent components, and civil/architectural structural use of glassy polymers.