Date of Award

2021

Degree Type

Thesis

Degree Name

Master of Science in Mechanical Engineering and Applied Mechanics

Department

Mechanical, Industrial and Systems Engineering

First Advisor

Arun Shukla

Abstract

The effects of long-term exposure to a sea-floor depth ocean environment on the mechanical behavior of carbon-fiber / epoxy (CFE) continuous filament-wound composite tubes were investigated experimentally. Using a novel high pressure accelerated aging vessel and the Arrhenius relationship for water diffusion into a polymer matrix composite, the acceleration factor was determined to be approximately 21.5; that is one day of aging in lab at 70°C represents 21.5 days of real life service at 3°C. Specimens were aged for 0, 9, and 24 days which represent 0, 193.5, and 516 days of service. The specimens were sealed and half were subjected to external hydrostatic pressure until they imploded, and the other half were pressurized to 80% of the average implosion pressure previously determined and subjected to a strong impulse by means of a nearby explosive detonator. The behavior of the tube immediately before and during its collapse was recorded by high frequency pressure transducers and high speed digital stereo photography. In both the hydrostatic-initiated and explosive-initiated implosions, the composites did not significantly degrade nor change their properties with aging. These observations are in contrast to a previous study with nearly identical conditions except aged at atmospheric pressure. The results from this current study are supported by the conclusions of another study which studied CFE laminate aging under identical conditions. An additional set of experiments were performed using the same preparation methods and similarly sourced and dimensioned samples to investigate the impact of long-term deep-sea immersion on the composite’s ability to hold internal pressure. The specimens were sealed and internally pressurized until leak or burst, and the phenomenon recorded by the same camera and transducer setup. It was found that the high pressure aging process did not significantly change the bursting pressure of the CFE tubes, but did significantly affect the fracture characteristics, which may have implications on non-bursting failure such as leaking.

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