Effective design of composite tanks is challenged by the ability of accurately determining onset of specific events such as: crack formation, leakage, slippage of gas between dome and valve assembly, and rupture of tank. Other challenges pertain to accurate determination of: ply angle distribution; residual stresses due to winding and curing; tank reliability due to scatter in manufacturing parameters, defects, and material properties; strength allowables for risk reduction; tank autofrettage; addressing variability in tank performance considering “As-designed” versus “As-built” and “As-is”; and tank certification. Some composite tank structures undergo numerous temperature / pressurization cycles causing an onset of delaminations and micro-cracking. Delaminations occur because of the differential movement of the layers caused by CTE mismatches between the layers. After successive cool-and-heat cycles, the weak adhesive bond between the layers degrades and breaks.

Typical filament winding details used as input

Tank leakage tends to occur when micro-damages in the tank wall materials exceed tolerable levels, which may cause catastrophic tank failure. Production cost and weight of tanks are increased to improve durability and reliability of these structures.

It is addressed by use of multi-scale based progressive failure analysis with robust design. Most finite element analysis (FEA) solvers assess damage at the lamina level whereby damage initiates at lower scale in the fiber, matrix, and interphase. These challenges are addressed by AlphaSTAR through an integrated capability that couples winding analysis with multi-scale progressive failure analysis including modeling of defects and uncertainty analysis. GENOA Filament Winding, progressive Failure Analysis and robust design modules are used to model, analyze, and design COPVs with minimum weight and with improved durability and reliability.

• Reduce number of design and certification tests by relying on accurate analysis and simulation methods.
• Reduced weight.
• Increased durability and reliability.
• Enable large scale production of tanks by eliminating/controlling sources that produce anomalies.

Testimonials

[1] Christopher P. Keddy, “Composite Overwrapped Pressure Vessel Modeling and Analysis”, White Sands Test Facility, Johnson Space Center, July 2008.