Michael Pinto

Mitigation of pressure pulses from implosion of hollow composite cylinders

An experimental study on the underwater collapse of composite tubes with polymeric coatings is conducted in an attempt to mitigate the implosion pressure pulse released. Experiments are performed in a pressure vessel designed to provide constant hydrostatic pressure during collapse. Filament-wound carbon-fiber/epoxy tubes are studied with polyurea coatings of different thicknesses on the interior and exterior of the tube to explore the effects of these configurations on implosion pulse mitigation. 3-D Digital Image Correlation (DIC) technique is used to capture the full-field deformation and velocities during the implosion event. Local pressure fields generated by the implosion event are measured using dynamic pressure transducers to evaluate the strength of the emitted pressure pulses. Local pressure data and DIC results are used to obtain a measure of normalized energy released during implosion. Results show that thick interior coatings significantly reduce the energy released in the pressure pulse by slowing the collapse and softening the initial wall-to-wall contact. In contrast, thick exterior coatings increase this energy by suppressing damage, thereby reducing the energy absorption capacity of the structure.

Experimental Investigation on Underwater Buckling of Thin-Walled Composite and Metallic Structures

An experimental study on the underwater buckling of composite and metallic tubes is conducted to evaluate and compare their collapse mechanics. Experiments are performed in a pressure vessel designed to provide constant hydrostatic pressure through the collapse. Filament-wound carbon-fiber/epoxy, glass/polyester (PE) tubes, and aluminum tubes are studied to explore the effect of material type on the structural failure. Three-dimensional digital image correlation (DIC) technique is used to capture the full-field deformation and velocities during the implosion event. Local pressure fields generated by the implosion event are measured using dynamic pressure transducers to evaluate the strength of the emitted pressure pulse. The results show that glass/PE tubes release the weakest pressure pulse and carbon/epoxy tubes release the strongest upon collapse. In each case, the dominating mechanisms of failure control the amount of flow energy released.

Mitigation of Energy Emanating from Imploding Metallic and Composite Underwater Structures

An experimental study was conducted to investigate the energy mitigation of hydrostatically initiated implosions of composite and metallic structures. Energy mitigation is achieved by placing polyurea coatings of different thicknesses at different locations onto imploding structures. The implodable structures are made of AL 6061-T6 and carbon-fiber/epoxy composite tubes with seven layers of unidirectional carbon fabric reinforcement arranged in a [±15/0/±45/±15] layup. The implodable specimens are sealed from the water with end caps and suspended inside a large pressure vessel that simulates a free-field marine environment. The hydrostatic pressure inside the pressure vessel was gradually increased until the specimens became unstable and collapsed. The collapse velocities and localized pressures of the imploding structures were captured during the experiments. Two high-speed cameras recorded the implosion phenomenon while dynamic pressure transducers measured the emitted pressure pulses. The results of these experiments show that polyurea can strongly reduce the pressure pulses emitted during the implosion; in turn, mitigating the emanating implosion energy. Moreover, the overall increase in performance, regarding energy reduction, is due to the polyurea coating and not the higher mass of the implodable structures. Placing polyurea coatings in the interior of the implodable structure leads to a higher performance regarding mitigating released energy than exterior placed coatings. Lastly, considerable increase in exterior coating volumes may result in adverse effects such as increasing structural velocity and energy emitted.

Instabilities in Underwater Composite Structures: Hydrostatic and Shock Loading

Abstract Experimental studies on the underwater buckling of composite tubes are conducted to evaluate and compare their collapse mechanics. Experiments are performed in a pressure vessel designed to provide constant hydrostatic pressure through the collapse. Filament-wound carbon-fiber/epoxy and glass/polyester tubes are studied to explore the effect of material type on the structural failure. Mitigation strategies are explored through polyurea coatings of different thicknesses on the interior or exterior of the tube to explore the effects of these configurations on implosion pulse mitigation. Shock-initiated implosions are also studied, where underwater explosives are used to load the structures with shock waves of varying magnitude. Three-dimensional digital image correlation technique is used to capture the full-field deformation and velocities during the implosion event. Local pressure fields generated by the implosion event are measured using dynamic pressure transducers to evaluate the strength of the emitted pressure pulses. These studies make a significant contribution to the state-of-the-art in the dynamic implosion of composite structures.Experimental studies on the underwater buckling of composite tubes are conducted to evaluate and compare their collapse mechanics. Experiments are performed in a pressure vessel designed to provide constant hydrostatic pressure through the collapse. Filament-wound carbon-fiber/epoxy and glass/polyester tubes are studied to explore the effect of material type on the structural failure. Mitigation strategies are explored through polyurea coatings of different thicknesses on the interior or exterior of the tube to explore the effects of these configurations on implosion pulse mitigation. Shock-initiated implosions are also studied, where underwater explosives are used to load the structures with shock waves of varying magnitude. Three-dimensional digital image correlation technique is used to capture the full-field deformation and velocities during the implosion event. Local pressure fields generated by the implosion event are measured using dynamic pressure transducers to evaluate the strength of the emitted pressure pulses. These studies make a significant contribution to the state-of-the-art in the dynamic implosion of composite structures.

Differences in the Hydrostatic Implosion of Metallic and Composite Tubes Studied Using Digital Image Correlation

A comparative experimental study is conducted to investigate the mechanisms and energies associated with the hydrostatic implosion of hollow cylinders of different materials. Experiments are performed in a 2.1 m diameter spherical pressure vessel designed to provide constant hydrostatic pressure through the collapse event. Aluminum, glass/polyester, and carbon-fiber/epoxy tubes are studied to explore the effect of material type on the modes of failure. 3-D Digital Image Correlation technique, which is first calibrated for the underwater environment, is used to capture the full-field real-time deformation during the implosion event. Dynamic pressure transducers measure the pressure pulses generated by the implosion event and evaluate its damage potential. Using these measurement techniques, the differences in mechanisms of failure as well as their effects on the local pressure history are characterized.