Design and testing of a composite pressure hull for deep autonomous
underwater vehicles
Abstract
This paper outlines the design and testing process of the hull of a
deep small Autonomous Underwater Vehicle (AUV), rated at 2000m depth.
Many existing AUV pressure housings use aluminum or other isotropic
traditional metals, instead of composites due to the complexities of the
design of composites at such big load. The research at hand explains the
process of design starting from setting the geometrical constraints for
the design to mass production. To the best of the authors’ knowledge,
none of the previous studies has presented such detailed description of
the work. Carbon fiber reinforced epoxy material was chosen thanks to
its high strength-to-weight ratio and similarity of its compressibility
to sea water. Material characterization was performed to obtain the
material properties under loading conditions using a modified method of
the Combined Loading Compression testing technique. A specific fixture
was designed and manufactured to test filament-wound tubes. An
analytical model was developed using MATLAB, a finite element model was
created using ABAQUS, and the results of the two models were compared. A
set of recommendations was introduced for the stacking sequence to
provide the lowest possible stresses, regardless on the diving depth of
the vehicle. Afterwards, a quality control set of tests was conducted,
including seawater absorption under high pressure and void analysis
using destructive and non-destructive tests. Pilot samples were
manufactured and tested in a pressure vessel, where it was cycle-tested
and inspected using visual and ultrasonic testing. Other samples were
fail-tested and showed a failure at ∼93% of the expected failure load.
Such range can be considered good to provide safe operation for the
vehicle at the designated depth, given that the factor of safety
included covers more than 7% of the failure load. The proposed design
methodology has shown that CFRE can be safely used even at such high
depths.