Some considerations of fracture mechanics applications in ships design, construction and operation

Abstract

The structural performance demands placed on present day high performance ships and some types of shipboard liquid natural gas (LNG) cargo containment systems requires the use of new materials which can perform under higher loadings and severe service environments. Such critical designs must be accomplished while maintaining a high structural reliability and decreased life-cycle costs. For high performance ships these critical designs can be accomplished with damage-tolerant design procedures which provide for redundant load paths and/or crack arrest capabilities. The ship construction and maintenance requirements must also be included in the design because of their effect on the structural life performance of the high performance ship. For shipboard LNG cargo containment systems modified LEFM (linear elastic fracture mechanics) is used in the design phase. The paper discusses the philosophy of a fatigue and fracture control plan for high performance ships and the use of modified LEFM for shipboard LNG cargo containment systems. Current applications of a fatigue and fracture control plan are discussed. The types of shipboard cargo containment systems designed using the modified LNG approach are described. The paper addresses the need for an integrated life time quality assurance program. Such a program is shown to require a synthesis of materials characterization, structural analysis and nondestructive testing. A service performance feedback loop will assist the designers in continually improving the then governing design criteria. In addition, areas requiring further work and possible future applications for fatigue and fracture analysis will be discussed.