Modeling of permeation and damage in graphite/epoxy laminates for cryogenic fuel storage

Abstract Polymer–matrix composite (PMC) materials are ideal for aerospace structural applications, such as cryogenic fuel tanks of reusable launch vehicles (RLVs) and expendable launch vehicles (ELVs), due to their high strength-to-weight and stiffness-to-weight ratio. For the confident application of these materials, it is necessary to evaluate the permeation of cryogenic fuel caused due to transverse matrix cracks in conjunction with inter-ply delaminations resulting in an intersecting network of passages. In this paper, an expression for predicting delaminated crack opening displacement (DCOD) is derived based on first-order shear laminate theory applied to five-layer and three-layer models. The DCOD obtained using both five-layer and three-layer model is verified using a two-dimensional finite-element analysis. A mathematical model to predict permeability in graphite–epoxy laminate system (IM-7/PETI-5) is developed using Darcy's law for isothermal, viscous flow of gases through porous media. The results obtained from both five-layer and three-layer model are used as input to the permeability model. Using this model, the permeability is calculated for an orthotropic laminate lay-up for a given delamination length, crack density and loading conditions.