ATTEMPTING TO ESTABLISH DESIGN MARGINS FOR GLASSY POLYMERS IN CRITICAL STRUCTURAL SERVICE Bart Kemper Kemper Engineering Services Baton Rouge, LA Kaylie Kling Williams Lockheed Martin West Palm Beach, FL ABSTRACT The existing code procedures for glassy polymers are in ASME Safety Standard for Pressure Vessels for Human Occupancy (PVHO-1). The current service spans hostile conditions in the North Sea to controlled medical environments. These procedures are based on an empirical method and do not use material properties. The system is locked into specific shapes and cannot be adjusted to account for yield strength, ultimate strength, and other material considerations. An ASME task group is developing a Design By Analysis (DBA) methodology in order to allow for optimization in current service and innovation in other service. This paper presents the attempt to develop design margins as part of an overall risk assessment process that considers material properties, service conditions, and other factors not currently incorporated in the existing design method. Historical work used to develop the current system are analyzed using modern methods to attempt to quantifiably determine the existing design margins. The challenge is the empirical method implicitly relies on polymer manufacturers to greatly exceed the code. This, coupled with different modes of failure, results in no direct manner to compare PVHOs to conventional ASME pressure vessels design margins. Keywords: PVHO, pressure vessel, acrylic, polymer, design NOMENCLATURE CF temperature-based Conversion Factor Df diameter of opening in window flange Di diameter of the interior of the window r radius to the shell’s mean thickness STCP Short Term Critical Pressure t thickness of the glassy polymer Tg glassy transition temperature window transparent glassy polymer component viewport assembly including window, seat, and seals FIGURE 1: AN ACRYLIC DOUBLE-BEVELED FLAT DISC WINDOW FOR A HYPERBARIC MEDICAL CHAMBER. IT WAS INTENTIONALLY OVERPRESSURED UNTIL A FAILURE OCCURRED AT 49 MPA (7,100 PSIG). THE CRACKS DEVELOPED WHERE THE VIEWPORT METAL SEAT (LOW PRESSURE SIDE) CREATED A STRESS CONCENTRATOR. 1. INTRODUCTION Glassy polymers have been in use since the 1930s. They were initially used to replace glass in aircraft to save weight.[1] An example is shown in Figure 1, where a window cracked along its entire viewport seat circumference at over 7 times its operating pressure but did not fail catastrophically, unlike glass. The clarity allows the operator to see any cracks or defects as they form. Because the glassy polymers tend to crack without shattering, it allows the operator to respond by reducing internal pressure (for a chamber), begin ascending (for a submarine), or reduce altitude (for aircraft). [1, 2] Today many consumer products such as safety glasses and drinkware use glassy polymers for these reasons. Recently, glassy polymers have been key in developing air flow barriers to combat the spread of COVID19. The challenge has been developing a broad understanding of its engineering use in a manner comparable to conventional engineering materials such as steel, aluminum, and concrete. Proceedings of the ASME 2021 International Mechanical Engineering Congress and Exposition IMECE2021 November 1-5, 2021, Virtual, Online IMECE2021-71836 Copyright © 2021 by ASME V013T14A020-1 Downloaded from http://asmedigitalcollection.asme.org/IMECE/proceedings-pdf/IMECE2021/85697/V013T14A020/6829257/v013t14a020-imece2021-71836.pdf by Southwest Research Institute, Bart Kemper on 27 January 2022