| A general design methodology was presented for material selection of pressure vessels with Ti-6Al-4V tapered end-caps for deep ocean applications under external hydrostatic pressure of 10,300 psi. Ti-6Al-4V, APC-2/AS4, and Graphite/Epoxy were three candidate materials. Parametric study was performed to determine the optimum tapered radius on end-caps since it was found that it could increase the performance of the pressure vessel. Stress and buckling analyses were performed taking hygrothermal effects into account. Based on finite element analyses (FEA) results, weight, ease of fabrication, mechanical performance, and cost, APC-2/AS4 was selected as a material system for the pressure vessel. The effects of end-caps with radial clearance on the performance of the APC-2/AS4 pressure vessel were investigated. It was shown that using end-caps with radial clearance could increase the performance of the pressure vessel by 12.5%. Ti-6Al-4V end-caps were designed under 10,300 psi external hydrostatic pressure.; For the SAUVIM project, APC-2/AS4 pressure vessels were design for a design pressure of 8,976 psi. The pressure vessels have total lengths of 21&inches; and 19&inches;, inner diameter of 13&inches;, and wall-thickness of 1.188&inches;. The combination of radial and tapered end-caps was used for the SAUVIM pressure vessels to increase the performance, avoid possible leakage of the pressure vessels during operations.; In-situ thermoplastic composite filament winding/tape-laydown set-up was designed and fabricated to manufacture the pressure vessels. A scaled APC-2/AS4 pressure vessel was designed for 3,500 psi, manufactured, and successfully tested at 3,500 psi. The strain results from experiment and FEA were in good agreement. The 19&inches; pressure vessel was manufactured and tested at high pressure and failed at 5,500 psi primarily due to manufacturing defects. The experimental and FEA strain results were comparable up to 4,000 psi, i.e., just before the initiation of damage.; FEA was performed to design the frame of SAUVIM vehicle. Different load and boundary condition cases were considered. The stress factor of safety was calculated based on the weldment strength of the aluminum (12,000 psi). The minimum factor of safety of around 4.4 was achieved when the vehicle was in the water, thrusters were working, and arms were at the retracted position. |
