Regarding the use of High Strength Low Alloyed (HSLA) Steels, it has been documented that todays merchant ships are prone to crack initiation and propagation in stress concentration areas mostly due to fatigue loads.
This project aims to investigate two novel ideas concerning ship structures. First the introduction of High Strength Low Alloyed Steels (HSLA) in specific structural details in order to deal with the major issue of crack initiation and propagation in critical areas of ships and second the replacement of specific structural parts of the ship with composite materials.
In this respect it is envisaged to replace Grade A or AH steels by HSLA steels with high toughness properties in specific areas of the ship structure, thereby reducing the risk of cracks developing in stress concentration areas. Concerning the use of composite materials, it is envisaged that they could replace parts of the steel structure, such as superstructures, piping and other non-critical parts. Composite materials can replace steel in certain parts of the ship thereby reducing weight and corrosion effects, without sacrificing structural integrity.
Stronger ships with fewer cracks
Today's passenger and cargo ships are increasingly large and complex. Replacing conventional steel with other materials promises to minimise their susceptibility to cracking in areas where stress concentrates due to fatigue loads.
Propagation of cracks can have catastrophic consequences in large passenger and cargo ships. EU-funded scientists are investigating two solutions depending on the structural component involved with work conducted in the scope of the project 'Materials onboard: Steel advancements and integrated composites' (http://www.mosaicships.com/ (MOSAIC)).
Researchers are replacing Grade A or AH steels with either high-strength low-alloy (HSLA) steels or composites. HSLA steels with better mechanical properties and resistance to corrosion are targeted for large structural components in areas of stress concentration. Lightweight composites with resistance to corrosion are envisioned to replace piping or other non-critical parts.
MOSAIC is studying design, fabrication, quality control and performance as well as cost to determine the feasibility of adopting the new materials. The project does not cover fire and safety, which will be addressed in further research.
During the first 18 months, the team decided on three test cases for each material class and began characterising various materials within them for suitability to the chosen applications. The composite has been chosen and the HSLA will be finalised in the next few months.
Three welding technologies are under study to join the HSLA components to conventional steel. Joining methods and configurations have been defined for the composite applications with the aid of finite element method (FEM) models. The team has also developed global FEM models of the ships to be used in determining local loads in each application case.
Replacing materials in areas prone to cracks is expected to have substantial benefits in many areas. Obviously, with fewer cracks, maintenance and repair costs will be reduced as will time out of service. Fewer defects will also increase safety. Lighter-weight vehicles will facilitate lower fuel consumption leading to both cost and environmental benefits in terms of reduced emissions. Taken together, MOSAIC solutions will reduce the lifetime costs associated with production, operation and maintenance of large merchant ships.