CompositesWorld
Issue link: https://cw.epubxp.com/i/632301
63 CompositesWorld.com co-bonded to the tank. Bonding the futed-core skirt to the tank's cylindrical dome tangent point required the integration of an arrowhead-shaped softening strip that had good shear, peel and expansion properties (see the drawing inset, p. 61). "We developed a 3D polymer-infused carbon part that ft between the futed-core skirt and the tank and remained compliant at low temperatures," McCarville says. Before the 34-month CCTD program ended, both the 2.4m and 5.5m tanks underwent full- scale, ground-based cyclical testing at cryo- genic temperatures, including ambient and cryogenic pressure tests. Additional ground tests simulated pres- surization plus fight loads — for these, axial/shear mechanical loads were applied through the skirts on the 5.5m tank. As a conse- quence of successful testing, "we raised the technology and manu- facturing readiness levels from a level of 3 at the outset to 6 at the completion of the program," McCarville says. Te project produced the largest composite tank ever manufactured via AFP and then cured out of the autoclave. Tat said, challenges remain. The next step: Real-world skirt tooling On the 5.5m tank, relatively simple metallic end-fttings were used to join the constant cross-section fute trapezoids to the test stand. But on a launch vehicle, the futes will require weight-efcient, Cryotank's Fluted Core Skirt possibly composite fttings that will most likely complicate fute geometry and, therefore, tooling. "Fluted core, similar in shape to hat stringers, has hollows that need [structural] support during high-temperature cure," McCa- rville explains. Further the tooling must support head pressures generated when the robotic AFP places the outer skin onto the futes. During the CCTD program, Boeing used a proprietary prototype tooling method that was sufcient for constant cross- section futes, but does not readily lend itself to real-launch vehicle end-fttings. "Now, we are working on designing end-fttings that allow for [post-cure] removal of a futed-cure mandrel out of trapped volumes, as we will need for a real-world launch vehicle tank," he says. To address this challenge, NASA funded a Small Business Inno- vation Research (SBIR) contract on Tooling for Composites II - Fluted Core Demonstration. McCarville says, "Tat's the function of small business innovation research projects like this, to help mature new innovative technologies that can be used to make next-generation products." CW will report on the results of the Fluted Core Demonstration research in its March 2016 issue. Read this article online | short.compositesworld.com/ CCTDCryotk Read about efforts to develop removable mandrels for use in the CCTD cryotank layup in "Janicki Industries: Breaking the mold" | short.compositesworld.com/zke0pgcU Co-cured tank and skirt The assembled skirt and tank, after skirt co-cure was completed. Although the tank and skirt were judged a success, work will continue toward more practical tooling for the futed core. Source | Boeing R&T; ABOUT THE AUTHOR Johanna Knapschaefer, a bilingual (English/Japanese) writer based on Boston's North Shore, writes about design and construction of buildings and infrastructure as a correspondent for Engineering News-Record, McGraw-Hill Construction, Architectural Record and other publications.