‘Investigations on Strength and Sustainability of Nonmetallic Laminated Composite Ship Structure

Abstract

Composite materials have emerged as a superior structural material having application in all spheres of life. These have applications in every sector and essentially in marine environment, where high strength to weight ratio and noncorrosive nature of the material has great importance. Subsequently there has been a major shift in use of structural materials from steel to composite materials in marine structures. Composite materials are engineered materials made from two or more constituent materials that are combined at a macroscopic level to produce a material with characteristics different from the individual components. When both the matrix and fibre are not of metallic origin, such composites are called as nonmetallic composites. Glass Fibre Reinforced Polymers (GFRP), Carbon Fibre Reinforced Polymers (CFRP) and Aramid Fibre Reinforced Polymers (AFRP) are common nonmetallic composite materials used for marine structural applications. These are used in laminate form in ship hull construction.In the present study, a design philosophy based on strength and sustainability of composite laminates has been proposed for selection of composites for ship hull construction. For this purpose, an index based on strength of composite laminates and an index based on sustainability of composites has been tabulated and materials need to be selected based on these indices. Both the indices had been constructed as a composite indicator. Index based on strength called as ‘Strength Index’ has been developed based on the index values of various strength parameters. Index based on sustainability called as ‘Sustainability index’ has been developed based on the index values of the composites based on the environmental impact of various phases of a ship’s life cycle. Nine non metallic composites have been considered in the present study. Accordingly strength parameters identified are bending strength, buckling strength and impact strength have been found out. Environmental impact during the manufacturing phase and disposal phase of composites has been found out. Based on these index values, indices based on strength and sustainability has been constructed respectively. Based on these indices, ranks have been assigned in such a way that, lower rank corresponds to higher strength and lower environmental impact. This also means lower the rank, higher the acceptability of the composite laminates. Using these two indices a two dimensional assessment of composites has been conducted. In this study both the indices have been superimposed to get strength index versus sustainability index plot. Analysis of this plot is the core of the design philosophy, ‘Design for strength and sustainability’. According to this design philosophy, the composite which has the least strength index and sustainability index rank should be selected for designing so that the structure will be strong and at the same time have a low impact on the environment. This procedure can be extended to any number of composites in the marine area or to composites that has application in other areas.