Composite reinforcement for naval ships: concept design, analysis and demonstration

摘要

This thesis outlines the development of composite reinforcement technology for a ship's aluminium alloy superstructure. The work objective aimed to alleviate stress concentration in parts of the superstructure prone to fatigue-induced cracking. This is a novel approach to ship repair, which promises reduction in the cost of maintenance primarily due to greater efficiency and lower cost of repair. The work was conducted over approximately 12 years. It commenced in the late 80s with laboratory research and development and concluded in 2000 after completion of a seven-year trial on board a navy ship. Two carbon fibre composites, (5 m x 1 m consisting of a 25-ply laminate), were adhesively bonded to the 02-deck on the port and starboard sides. It was found that upgrading the structure using composites was effective, making it able to withstand service fatigue stresses. Finite element modelling and strain measurements on board the ship showed that critical stress concentration could be alleviated through stress redistribution. For the duration of the trial, no cracking of aluminium alloy deck in the vicinity of the reinforcements was reported. Both composite reinforcements exhibited good performance and remained in service after the end of the trial. However, the marine environment did cause some non-structural, edge debonding of the glass fibre reinforced overlay at the composite-metal interface. This overlay was designed to provide surface protection to the underlaying carbon reinforcement. Bond degradation was patchy. It occurred after about three years in service, most probably due to a combination of thermal cycling (solar heating/cooling) and water ingress at the interface. A new edge sealing method restored its durability and it required no further attention. This experiment was successfully demonstrated on board an active navy ship. The work proved that an effective and durable repair of a ship structure using non-metallic repair technology is feasible. Composite reinforcements prevented deck cracking and removed any need for welded repairs, thereby reducing the cost of ship maintenance. For further cost reduction it is recommended to adopt the principle of reverse engineering to simplify the technology for dockyard use.