Gas Permeability of 3D Printed Thermoplastic Composites for Cryogenic Applications

Abstract

Thermoplastics have shown promise as a choice of material for production of lightweight structures for cryogenic storage. To fully utilize thermoplastics for such applications, cryogenic fuel leakage through transverse cracks in these structures must be studied. Thermoplastic composites (carbon fiber reinforced PEEK and Nylon) were 3D printed using fused deposition modeling. Test specimens were thermally cycled from ambient (23ºC) to cryogenic (-196ºC) temperatures and gas permeability measurements were conducted at selected cryogenic cycles. Results show that carbon fiber/PEEK specimens had the lowest gas permeability after 50 cryogenic cycles with no through-thickness crack networks. The gas permeability of 3D printed thermoplastic composites was several magnitudes lower than the leak rate allowables for different launch vehicles. Tensile tests, post cryogenic cycling, revealed a reduction in the tensile strength and modulus of the 3D printed specimens with CF/PEEK having the best mechanical and permeability performance.