MATERIALS ASPECTS OF DAMAGE TOLERANCE AND RELIABILITY OF SHIP STRUCTURES AND COMPONENTS

The design and development process prior to the fabrication of maritime structures such as merchant ships, naval surface ships and submarines include the specification of a range of materials required to perform under most adverse conditions of environment and operational loads. The damage tolerance and reliability of such structures can only be assured through appropriate materials selection, application of regorous testing methodologies and through-life inspection and monitoring. The importance of the consideration of damage tolerance and reliability of maritime structures can be gauged by the consequences of in-service failures; for example, the break-up of merchant ships resulting in environmental disasters, loss of lives and wartime damage of naval ships and submarines. Factors that lead to service failures include corrosion, fatigue, corrosion fatigue, low toughness and poor design, and often these factors occur in combination. The range of materials used in maritime structures is diverse and includes mild steel (ship) plate, micro-alloyed steels, aluminium alloys and monolithic and foam sandwich glass fibre laminates. These materials all have different responses to the environmental and loading conditions and consequently extensive materials testing programs are necessary to put damage tolerance and reliability indicators in place. This paper addresses the materials and testing aspects of damage tolerance and reliability assessment of maritime structures, and deals broadly with corrosion and corrosion fatigue testing; fracture toughness testing; measurement of residual stresses within the structure; damage assessment and life calculations. The paper discusses testing methodologies that obtain essential property data for various materials under a range of environmental and loading conditions. The paper briefly addresses the application of property data to the prediction of the behavior of maritime structures and components as well as application to life prediction methodologies. The performance of the maritime structures and components in service can be monitored by many methods. The resultant outputs from the monitoring systems can be indicators of the development of damage within the structure and used to predict the behaviour of the damaged structure for reliability assessment. The future needs for the monitoring of maritime structures and components are discussed and some examples of monitoring methods will be presented.