Manufacturing of stitched polymer matrix composites using barrier layers for cryogenic applications

Description:

Overview of technology

A process for manufacturing cryogenic vessels to reduce excess leakage of cryogen gas in extreme environmental applications.

Background

Unstitched composites have been used for the fabrication of cryogenic fuel tanks. This requires several cures and several non-destructive evaluations at each stage of the fabrication process to complete a fully assembled cryotank. The bonded joints for the flutes and skirts must withstand very large peel stresses, which form the primary failure mechanism in these bonds. The key technology that makes this structural integration breakthrough achievable is stitched composites. Since all materials in the stitched assembly are dry, there is no out time or autoclave requirements as in prepreg systems. This stitching provides a necessary through-thickness reinforcement to enhance interlaminar tensile and shear strengths.

Cryogenic propellant tanks undergo a combination of large thermal and mechanical stresses, which lead to transverse micro-cracks that initiate delamination in the PMC tanks. A mismatch in the coefficients of thermal expansion of the metal and polymer matrix results in the debonding of the liner from the tank, leading to excessive permeation. Liner-less designs have included the use of woven textile material to improve drapability and wetting of fibers in the matrix for stronger adhesion. Due to their very low cured thickness, these piles do not provide the necessary energy for a crack to propagate.

Description of Technology

Researchers at Mississippi State University have developed a manufacturing system of dry thin piles into stitched composites as a barrier layer. In doing so, they are toughening the resin using nano-graphene to increase the ductility of the resin-rich areas and impede micro-crack growth in these regions.

This technology incorporates a combination of thin piles and nanographene toughened resin into stitched composites that allow for a more precise measure of the permeability of stitched composites after several cryogenic cycles. It also allows for a more precise measurement of permeability of stitches composites under biaxial stresses at cryogenic temperatures.

Benefits

This technology is important for any application that requires lightweight structures in a cryogenic environment.

Applications

This technology can be used in a variety of fields including cryogen storage and transportation, pressure habitats, and bladder, piston, or diaphragm accumulators. Mississippi State University is currently seeking companies that could benefit from a stitched composite in cryogenic temperatures as a barrier layer.