Modeling of Damage in Graphite/Epoxy Laminates forCryogenic Fuel Storage

摘要

It is now well-established that composite materials are ideal for aerospace structural applicationsrnwhere high strength-to-weight and stiffness-to-weight ratios are essential for the success of thernmission. One such application is cryogenic fuel tanks for RLV and ELV. However, it is feasible thatrnwhen subjected to extreme temperature variations combined with dynamic structural loading,rntransverse matrix cracks in conjunction with inter-ply delaminations originating from the tips of theserncracks, result in an intersecting network of pathways that could allow fuel to permeate. In this study,rnan analytical expression for predicting delaminated crack opening (DCOD) is derived based on firstorderrnshear laminate theory applied to five-layer and three-layer models. Using this expression, thernDCOD is calculated for a cross-ply laminate with a given delamination length, crack density andrnloading conditions. The DCOD predictions for cross-ply laminate show excellent agreement withrnfinite element analysis results. In addition, an analytical expression for predicting permeability ofrngraphite-epoxy laminate system is derived based on Darcy’s law for isothermal, viscous flow of gasesrnthrough porous media in conjunction with the micro-crack model. The DCOD values predicted fromrnthe first-order shear laminate model are subsequently used as input to the permeability model. Usingrnthis model, permeability is predicted for a [0/902]S IM7/PETI-5 graphite/epoxy laminate lay-up for arnspecified delamination length, crack density, and thermo/mechanical loading condition. Modelrnverifications are carried out by comparison with finite element analyses.