Design and analysis of lightweight pressure vessels

This dissertation will examine near term and long term options to for constructing undersea pressure vessels that are light weight and durable. The research will focus on pressure vessels that are used in military applications. Products placed on a military vessel must survive extreme loads such as high depth pressures, underwater shock waves, and high speed flow. The ability to withstand these loads is critical because the failure of a pressure vessel at deep depths can result in a potentially catastrophic implosion.The use of 7000 series aluminums will be investigated as a near term option for manufacturing inexpensive pressure vessels with thin walls in this dissertation. Two new alloys, 7085 from ALCOA and an experimental unnamed 7000 series aluminum-scandium (Al-Sc) alloy from Surface Treatment Technologies Inc., will be an area of focus for this dissertation. Older alloys such as 6061-T6 and 7075-T73 will also be investigated to form a baseline against which the newer alloys can be compared.The use of sandwich composite construction will be investigated as a long term option for light weight pressure vessels. Composite sandwich construction is not widely used in undersea applications. This dissertation will address basic design, modeling, and validation testing issues that must be answered before composite sandwich construction gains acceptance in undersea applications.The majority of pressure vessels in extreme military environments are made from medium strength steel. Medium strength steels have good ductility and fracture toughness and are very durable as a result. A smaller percentage of pressure vessels are made from 5000 and 6000 series aluminums. 5000 and 6000 series aluminums also have excellent fracture toughness and ductility. Unfortunately, pressure vessels made from 5000 and 6000 series aluminums or mediums strength steels are very heavy because these materials have low strength to weight ratios. Most military applications are weight constrained so every pound that is added to the weight of a pressure vessel hull is a pound that has to be taken away from the payload.