Numerical method for predicting permeability of laminated composites at cryogenic temperature

The numerical method for predicting the permeability of a laminated composite based on matrix cracks is improved to meet the application at a cryogenic temperature. The number of the parameters that depends on experiments is reduced in this numerical method to save costs. The semianalytical damaged constitutive model of cracked plies, the crack density estimation method, the crack opening displacement estimation, and the effective leakage conductance calculation are improved by involving the temperature or thermal strain. Stiffness degradation of a carbon fiber reinforced plastic lamina with different thicknesses and temperatures is obtained by the proposed constitutive model to validate the effect of temperature; and the degradation of the transverse modulus is found to subside with the increasing temperature when the crack densities are the same. The effective leakage conductance of cross-ply laminates, under biaxial loading, is estimated at cryogenic and room temperatures by using three different average methods. The estimation results agree well with the available experiments in the specimens with a uniform thickness of cracked plies. The simulation results indicate that the easier occurrence of leakage at the cryogenic temperature is owing to the significant degradation of the stiffness at cryogenic temperature instead of the thermal strains.