Opportunities for Weight Reduction in Composite Marine Structures

Doktorsavhandling, 2015

Composite marine structures are desirable for a variety of reasons. Compared to traditional steel structures, they enable the construction of vessels with lower fuel consumption, higher top speed, better stability, lower maintenance, higher cargo capacity, or combinations thereof. All these characteristics are highly desirable, as they influence the energy efficiency and profitability of the vessel. One of the barriers for a more widespread adoption of composite marine structures is their acquisition cost. This PhD thesis deals with this barrier by exploring opportunities for further weight reduction. Reducing the weight of a composite structure reduces its acquisition cost and increases many of its financial benefits, making it more economically attractive. Opportunities for weight reduction were identified in three areas: operational limits, material characterization, and structural design. For each of these areas, an approach for weight reduction was investigated. For operational limits, the possibility of motivating values higher than the ones stated by design rules through reliability analyses was investigated. The results show that strength reliability analyses of fibre-reinforced plastic structures in tension are frail and uncertain, because uncertain details of the mechanical and probabilistic models, as well as definitions of laminate failure, highly influence the reliability estimates. Therefore, higher operational limits cannot be motivated for the studied cases. The highly sensitive and uncertain details should be the subject of future research. For material characterization, the possibility of motivating more accurate mechanical properties for composites through advanced measuring techniques was explored. The results show that digital image correlation systems, as well as strain measuring devices with a large strain gauge, can improve the accuracy of material characterization methods. Higher material characterization accuracy may improve material utilization, leading to structural weight reduction. For structural design, a method was developed to assess the weight reduction potential of searching the design space for lighter designs and modifying design constraints (motivating higher operational limits or more accurate mechanical properties). The results indicate that searching the design space is the most promising approach of these three.