Additive manufacturing of polymeric lox tank liner prototype and its characterization

Additive manufacturing (AM) has revolutionized material production by enabling the realization of complex geometries with shorter turnaround times. Engineering polymeric materials such as acrylonitrile butadiene styrene (ABS), polyetherimide (ULTEM), and carbon fibre reinforced polymer (CFRP), polyamide 6 (PA-6), and polyether ether ketone (PEEK) are utilized to realise 3D-printed products with a high strength-to-weight ratio. This study attempts to develop a prototype of a liquid oxygen (LOX) tank liner as a replacement for current aluminium alloy tanks used in cryogenic stages of launch vehicles. The primary objective is to reduce the weight of the upper stages for improved payload margin. Since propellant tankages contribute significantly to the mass of upper stages, replacing heavy metallic tanks with low-density composite tanks could result in significant weight savings. To investigate the feasibility of this approach, LOX tank liner prototypes were manufactured using two different materials, polyurethane (PU) and polyamide (PA), employing additive manufacturing techniques such as stereolithography (SLA) and selective layer sintering (SLS). The mechanical properties of PU and PA materials were evaluated at room temperature and in liquid nitrogen conditions. Hydro-proof pressure testing (PPT), ultrasonic testing (UT), and non-destructive testing using X-ray were performed to identify defects in the realized 3D-printed tanks. Permeability rates were verified through helium leak checks using the sniffing method. Structural analysis was carried out to evaluate the tank liner's structural and pressure loads and determine the optimal thickness of CFRP overwrap. The findings of this study will provide insights into the potential of additive manufacturing techniques for producing lightweight composite tank liners of actual size suitable for futuristic launch vehicle applications. The mechanical properties, defect detection capabilities, permeability rates, and structural analysis results contribute to understanding the feasibility of using 3D-printed polymeric tank liners for high-end applications.