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.

In the present paper the crack opening displacement associated with delaminations that initiate from a matrix crack in a graphite-epoxy laminate (IM6/3501-6) subjected to mechanical and/or thermal loading is calculated using the sublaminate-wise first-order shear laminate theory and verified using a two-dimensional finite element analysis. The delamination induced crack opening displacement (DOD) for known delamination length and crack density is predicted for [0/902]S laminate system with a matrix crack in the 90o plies and delaminations growing uniformly from the matrix crack tip in the 0/90 interfaces. The effect of immediate neighboring ply orientation on DOD is studied by predicting DOD for the [θ/902]S (θ =0o to 90o) laminate system. In order to study the effect of stacking sequence on DOD, two laminate stacking sequences, [0/θ/902]S and [θ/0/902]S (θ =0o to 90o) are examined. It is seen for the examined laminates that the lay-up orientation of the ply adjacent to the 90oplies affects the DOD, whereas the stacking sequence of the neighboring ply groups do not influence the DOD significantly.