Gas Permeability and Flexural Strength of Impacted Composites for Cryogenic Propellant Tanks

Abstract

Reusable composite cryogenic tanks may be used in next-generation space launch systems due to their several benefits, such as increased specific strength, tailorability, and low coefficient of thermal expansion. However, transverse microcracks within composites due to thermal stresses and barely visible impact damage can cause cryogenic fuel to leak through the walls of the tank. The objective of the present study is to evaluate the gas permeability of impacted and thermally cycled composites and correlate it to their postimpact residual strength. Cross-ply carbon/epoxy composites ([Formula: see text]) fabricated from unidirectional prepregs were subjected to 20 cryogenic cycles from ambient to cryogenic temperatures ([Formula: see text]). Barely visible impact damage at two different impact velocities ([Formula: see text] and [Formula: see text]) was imparted to the specimens at room and cryogenic temperatures before and after cryogenic cycling. The composites’ gas permeability, residual flexural strength, and absorbed energy were measured and correlated. Composite specimens subjected to impact at room temperature had higher gas permeability and absorbed energy with lower residual flexural strength. A linear relationship was observed between gas permeability, absorbed energy, and postimpact flexural strength. Two linear models to predict gas permeability with absorbed energy and flexural strength as variables have been presented for impacted and cryogenically cycled specimens with an [Formula: see text] value of at least 96%.