High performance, thin metal lined, composite overwrapped pressure vessel

Abstract

An innovative technology for composite overwrapped pressure vessels (COPVs) has been developed which significantly increases cost effectiveness, increases reliability, and reduces weight over state-of-the-art COPVs. This technology combines an innovative thin liner made of a metal having a high modulus of elasticity and a high ductility, a high-performance composite overwrap and a high-performance film adhesive at the overwrap / liner interface. The metal liner can be fabricated from readily available titanium alloy sheet and plate using a combination of spin forming and machining to fabricate components and electron-beam welding for tank assembly. The composite overwrap is filament-wound onto an adhesive-covered titanium liner and the overwrap and adhesive are co-cured in an oven to yield an integrated tank structure.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to composite overwrapped pressure vessels (COPV's) and their method of manufacture. More specifically, the present invention relates to high-performance COPV's including liners made of metals which exhibit high moduli of elasticity and high ductility, such as titanium alloys.2. General BackgroundThe basic technology for composite overwrapped pressure vessels with metal liners dates back to the late 60's and early 70's.High-performance fibers offer very high strength-to-weight ratios and are ideal for making lightweight pressure vessels. However, composite laminates fabricated with these fibers have relatively high permeability and cannot contain high pressure liquids or gasses or low pressure gasses for extended periods of time. Therefore, composite pressure vessels must have a liner to prevent leakage. The tank efficiency, as measured by its pressure multiplied by its volume divided by its weight (PV / ...

AI Technical Summary

Benefits of technology

It is an object of the present invention to produce a COPV which, when used in spacecraft, launch vehicles, or aircraft, effects significant savings as compared to current COPV's.

It is also an object of the present invention to produce a COPV with a liner made of a metal having a high F.sup.TY / E and a high ductility.

Problems solved by technology

Each key operation had to be optimized for use in an overwrapped pressure vessel application, because the strain levels in the metal are well above yield, which non-composite overwrapped metal tanks are not designed to withstand.

During the course of the development of the technology, several failures were encountered due to manufacturing techniques that were not capable of fabricating a liner with the proper characteristics.

Initial attempts to use industry-standard spun-dome processing (developed for all metal tanks) proved inadequate for this application.

The early cylinders were fabricated using a Tungsten Inert Gas (TIG) welding technique, which even after numerous refinements was not capable of consistently performing in this application.

This is critical because even the best high-temperature vacuum stress-relieve operations produce a very thin layer of oxygen contamination (FIG. 6) which has been shown to crack under high strains (early tanks which were vacuum stress relieved exhibited cracks, some of which penetrated through the liner).

Initially, three liner systems were considered, aluminum--the current state of the art, electroplated copper--a developmental technology with limited success in preliminary development with the potential for very low weight, and titanium alloy.

The titanium was selected over electroplated copper because of the high design / fabrication risk associated with the copper lined tank development.

The exact mode of failure cannot be determined because, despite efforts to suspend the tank with elastic cords to prevent secondary damage, there was significant secondary damage to the tank which masked the exact failure initiation site.

(1) There was a failure in the dome region of the tank on the end with the pressure inlet.

The impulse of this failure instantly sheared the bolts holding the tank to the plates attached to the elastic cords.

Also there was extensive fiber and liner damage in both domes.

Although there is no way to be certain exactly what happened, it is likely that the failure initiated in the liner dome at a radius of approximately 4" from the longitudinal centerline.

The initial failure probably released a propulsive jet of water which failed the bolts holding the tank in the elastic-cord-supported fixture and propelled the tank into the wall, thereby creating the extensive secondary damage.

Satellite life is limited by the amount of propellant which the spacecraft can deliver to orbit.

As the mass of the spacecraft increases, so does the size and cost of the launch vehicle required to launch the spacecraft.

Reduction in tank weight can mean the difference in launching with one class of launch vehicle versus another, which one mean dramatic differences in launch costs.

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