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

The design and development process prior to the fabrication of maritim e structures such as merchant ships, naval surface ships and submarine s include the specification of a range of materials required to perfor m under most adverse conditions of environment and operational loads. The damage tolerance and reliability of such structures can only be as sured 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 o f maritime structures can be gauged by the consequences of in-service failures; for example, the break-up of merchant ships resulting in env ironmental disasters, loss of lives and wartime damage of naval ships and submarines. Factors that lead to service failures include corrosio n, fatigue, corrosion fatigue, low toughness and poor design, and ofte n these factors occur in combination. The range of materials used in m aritime structures is diverse and includes mild steel (ship) plate, mi cro-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 m aterials testing programs are necessary to put damage tolerance and re liability indicators in place. This paper addresses the materials and testing aspects of damage tolerance and reliability assessment of mari time structures, and deals broadly with corrosion and corrosion fatigu e testing; fracture toughness testing; measurement of residual stresse s within the structure; damage assessment and life calculations. The p aper discusses testing methodologies that obtain essential property da ta for various materials under a range of environmental and loading co nditions. The paper briefly addresses the application of property data to the prediction of the behavior of maritime structures and componen ts as well as application to life prediction methodologies. The perfor mance of the maritime structures and components in service can be moni tored by many methods. The resultant outputs from the monitoring syste ms can be indicators of the development of damage within the structure and used to predict the behaviour of the damaged structure for reliab ility assessment. The future needs for the monitoring of maritime stru ctures and components are discussed and some examples of monitoring me thods will be presented.