CompositesWorld
Issue link: https://cw.epubxp.com/i/841219
JULY 2017 46 CompositesWorld FOCUS ON DESIGN • Two separate titanium hemispherical domes, the front one featuring an integrated 380-mm-diameter acrylic viewport. • A glass fiber composite outer shell, bolted to flanges on the titanium interface caps. • A landing skid structure, also attached to the interface caps. Nothing will be mechanically attached to, or penetrate, the composite hull other than the titanium caps. Deep-sea exploration — even in a well-designed, well-engi- neered, pressurized submersible — is not trivial and does carry with it substantial risk. e world record free-dive depth for a human is 214m (312 psi), and for most people the "safe" depth is probably half that. us, in the event of catastrophic failure of a submersible at any depth greater than even 250m, deepsea water pressure would instantly kill every passenger on board. And this is the primary concern of OceanGate and, by extension, Spencer Composites. Cyclops 2 faces potential failure in any one of three struc- tures: the composite hull, the titanium end caps and the acrylic viewport. OceanGate designed a real-time health monitoring system that will acoustically monitor the composite hull to detect the pings and pops that signal to the pilot the risk of potential failure. Strain gauges will measure the health of the titanium end caps, which will see a maximum axial end dome load of up to 22 million lb. e viewport, says Rush, because it is acrylic, fails opti- cally long before it fails structurally — and in this case, catastroph- ically — thus the crew will detect a problem visually first. In any case, the goal is to alert the pilot of potential catastrophic failure in time to enable movement of the craft to shallower, safer water. Designing, building the perfect cylinder e design of the Cyclops 2 hull, says Spencer, is based in large part on the strategy applied to Fossett's DeepFlight Challenger. ick- ness, he says, was estimated using micromechanics, and then verified with finite element analysis (FEA). Modeling was done in SolidWorks (Dassault Systèmes, Waltham, MA, US) and analysis was done with COSMOS/M, supplied by Dassault Systèmes subsidiary Structural Research and Analysis Corp. (Santa Monica, CA, US). e biggest challenge, Spencer reports, was developing a manu- facturable design that "would produce a consistent part with no wrinkles, voids or delaminations." And without use of an auto- clave. Spencer opted for a layup strategy that combines alternating placement of prepreg carbon fiber/epoxy unidirectional fabrics in the axial direction, with wet winding of carbon fiber/epoxy in the hoop direction, for a total of 480 plies. e carbon fiber is stan- dard-modulus Grafil 37-800 (30K tow), supplied by Mitsubishi Chemical Carbon Fiber and Composites (Irvine, CA, US). Prepreg was supplied by Irvine-based Newport Composites, now part of Manufacturing in a generous safety margin The carbon fiber/epoxy hull of the Cyclops 2 features alternating layers of UD prepreg in the axial direction, and wet-wound carbon fiber filaments in the hoop direction. The hull is 127 mm thick (5 inches vs. the 6 inches planned for Fossett's earlier craft) and has tested to 2.5 times the 6,500-psi service pressure. Travel to the Titanic and beyond Cyclops 2 will be used for scientific research, deepsea exploration and oil and gas exploration. Its first mission, scheduled for May 2018, will be to shoot photos and video of wreckage from the Titanic, which is located in about 3,688m of water in the North Atlantic. This rendering depicts the Cyclops 2 above the Titanic.