Future materials in the maritime industry

DNV GL looks into the future of shipping, in which new materials will play

According to the classification society, the revolution in materials technologies will have an eno rmous impact on ships, allowing them[ds_preview] to carry more payload at the same displacement as today, and at higher speeds using less energy. These capabilities are not science fiction; such a ship could almost be built today with existing technology – depending on the budget, however.

Beyond steel

Since the late 19 th century, steel has been the primary material for shipbuilding. This essential material is cheap and readily available. With a global recovery rate of more than 70%, steel is also the most recycled material on the planet. However, history suggests that significant developments in materials technology can have a dramatic transformative impact on the industry. Just as steel replaced wood and the microchip replaced the electron tube, emerging materials technology will enable owners to produce safer, lighter and maintenance-free vessels.

The shipping industry is increasingly looking towards technology to manage stricter regulations, rising fuel costs, tighter margins and increased maintenance costs. At the same time, the industry is expanding into deeper waters and operating in colder, harsher climates, exposing their personnel and assets to greater risk. Indeed, sub-sea activities are already pushing the material properties of steel to their limits. In order to take the next step within shipping operations, new materials may be the only solution.

Developments in composites and aluminium have been utilised in some segments, but these materials currently have no viable application for deep-sea shipping. For example, the use of glass fibre reinforced composites is currently very limited in deep-sea shipping, due to SOLAS’ requirements on fire performance. However, as equivalent fire safety measures are applied to composites, more interest among owners may be seen.

Lightweight materials

Glass Fibre Reinforced Plastics (GRP) and aluminium are being used on increasingly larger warships, subject to strict naval regulations and standards, and increasingly on major components in the civil maritime industry. Further developments in lightweight materials will allow for operations in more extreme conditions and extend the lifetime of a vessel significantly.

Graphene, the first ever two-dimensional material, was discovered around ten years ago. Made up of one-atom thick layers of carbon, a single strand of graphene is the thinnest material ever observed. Up to 200 times stronger than common steel, graphene is flexible, light, nearly transparent and an excellent conductor of heat and electricity. As it is both stronger and stiffer than any known material, it could be used to manufacture products and structures that would be a fraction of the weight and exponentially stronger than anything produced today. Graphene could also be used to strengthen polymer or metal composites.

Another exciting development within the field of lightweight materials is 3D woven fabrics. Until recently, the increasing application of composites to make structures lighter and more corrosion-resistant has been slowed by the inefficient manual joining processes used today. Improving the reliability and efficiency of composite joining processes requires replacing traditional hand-lay-up processes with new 3D weaving technologies. The new approach

to joining structures significantly simplifies the complexity of parts and reduces the number of components used, dramatically improving the viability of composite lightweight solutions.

Aluminium oxynitride or AlON represents another promising development in lightweight materials. Once considered science fiction, lightweight transparent alumina is now a reality. AION is a transparent polycrystalline ceramic that is optically transparent and about three times harder than steel of the same thickness. The material remains solid up to 1,200°C, and has good resistance to corrosion and damage from radiation and oxidation. Typical applications are domes, tubes, transparent windows, rods and plates.

Finally, the introduction of metal foam will change how ships are designed, constructed and operated. Metal foam dramatically improves the weight-to-stiffness ratio, energy dissipation and it will have a positive effect on a vessel’s vibration, thermal, and acoustic performance. Another advantage is the mitigation of buckling, both for rods and plates, which will help improve safety and reduce maintenance costs. Metal foam decreases density and weight while increasing apparent thickness – a new design variable in steel material selection.

By controlling density, the properties of steel components can be significantly modified, expanding design space for steel applications towards more collision resistant structures. Properly constructed, foamed components can have higher bending stiffness and weigh less than solid steel. A sandwich panel with steel faces of one millimetre with a 14mm metal foam core has a comparable bending stiffness of a 10mm solid steel plate, at merely 35% of the weight.

In less than ten years, graphene has gone from the lab into pilot products all over the world. Recent developments in graphene production methods indicate the feasibility of mass production from numerous raw materials, including environmentally friendly and relatively low-cost chemicals. For joining technology, adhesive bonding is common today, but one should see more widespread use in lightweight structures – not only for composite structures but also steel. Weaving technology, perhaps in combination with 3D printing, will also be used to find solutions for structural damage repair. Future applications for AION include sensor windows, transparent armour, insulators and heat radiation plates, opto-electronic devices, metal matrix composites, and translucent ceramics. In the future, cruise ships may have large structures made of transparent alumina to provide passengers with better views while staying in compliance with strength integrity regulations.

Intelligent materials

Intelligent materials will offer a broad range of benefits to the shipping industry, DNV GL expects. Structures embedded with millions of miniaturised »smart« sensors can generate vast amounts of information, which can be streamed to relevant onshore personnel. Friction-reducing riblet technologies not only reduce drag, but also help to mitigate risks associated with the transportation of invasive species from one ecosystem to another. Some intelligent materials are self-healing, able to sense cracks or failures before damage occurs, while functionally graded materials will contribute to the increased lifetime of vessels by eliminating corrosion and metal fatigue.

Self-healing materials are defined by their ability to detect, heal and repair damage automatically. Different types of materials, such as plastics, polymers, paints, coatings, metals, alloys, ceramics and concrete have their own self-healing mechanisms. Some materials may include healing agents, which are released into the crack-plane through capillary action. When a crack ruptures the embedded microcapsules, a polymerization process is triggered, bonding the crack faces. This technology can be utilised on any surface on a ship, including tanks and hard-to-reach structural areas.

Materials of the future will also have sensing capabilities that will allow them to provide information about their immediate environment and their own condition. Relevant sensing technologies include laser-based interferometry, LED-based optical sensors, spectroscopy and spectrophotometry. Advances in production will allow sensors to be manufactured on a microscopic scale. Today, sensors can measure as small as 0.05mm by 0.05mm, but as new manufacturing techniques are developed, they will become even smaller.

Intelligent materials also include smart coatings, which incorporate functional ingredients such as nano-particles, micro-­electromechanical systems (MEMS) and Radio-Frequency Identification (RFIDs), among others. These technologies enable self-repair, self-healing and sensing. In the future, smart coatings may incorporate pH sensitive microcapsules for corrosion monitoring and deliver corrosion inhibitors. Likewise, work to develop and produce »smart dust« – a network of microscopic wireless MEMS sensors – may provide a whole range of benefits to the shipping industry. These microscopic sensors act like computers that function together as a wireless network. Applications related to the maritime industry include tracking of sea surface temperatures and circulating currents, or monitoring of the corrosion rate of hull structures.

Over the past decade, researchers have turned to the natural world for inspiration in developing smart materials. For example, studies have shown that the unique properties of sharkskin not only reduce drag by 10%, they also hinder microscopic aquatic organisms from adhering to the shark. Riblet surfaces are made up of very small grooves with sharp ridges aligned with the mean low. Reducing friction is achieved by the reduction of the turbulent span-wise motion near the wall.

Developments on mimicking the properties of sharkskin riblets may soon lead to coatings that would reduce drag and limit the bio-fouling on surfaces, and prevent transportation of biological substances. The industry is also likely to benefit from developments in functionally graded materials. These types of materials have properties that change with location, e.g. surface properties are different to core material properties. Functionally graded materials may be used to inhibit the development of cracks, which can occur in engines, hulls or other vital parts of the ship. They can also have a unique ability to act as a thermal barrier, ideal for use on structures or engine parts exposed to high extreme temperatures.

While many smart materials already exist, further research and development is required to reduce manufacturing costs. For example, functionally graded materials remain prohibitively expensive due to existing limitations of the powder processing and fabrication methods. Solid, freeform fabrication techniques such as 3D printing offer greater advantages for producing functionally graded materials, but more work needs to be done.

Advances in sensing technologies will allow more sensors to be manufactured on a microscopic scale. While it is still unclear when these technologies will be commercially viable, future materials will have sensing capabilities allowing them to provide information about their condition and the immediate environment. In this context, the two technologies that have the potential to be used on a global scale, regardless of material, are smart coatings and smart dust.

Powerful materials

»Developments in this field will turn composite structures into huge capacitors, powering a ship using printable photovoltaic cells that cover the entire ship exterior,« DNV GL writes in its »Future of Shipping« report. Electric carbon nanotubes will carry an immense amount of current and minimise energy loss. Likewise, stricter environmental regulations may encourage the development of both electrical energy storage and on-board solar energy production, such as printable plastic solar cells that can significantly reduce energy consumption and reduce emissions. Work is being focused on increasing the efficiency of the organic thin film cells, while keeping the cost of mass production low.

Developments in carbon fibre and specially formulated polymers have enabled light electrical energy storage. The charge is stored electro-statically, rather than as a chemical reaction. The energy device then behaves more like a capacitor, or ultra-capacitor, than a battery. The device can store and discharge electrical energy in addition to being strong and lightweight, suitable for use in structures.

For power generation, the industry may turn to printable plastic solar cells. Solar cells can be printed directly onto steel or other surfaces, acting as photovoltaic material made from semi-conducting polymers and nano-engineered materials. The active material absorbs photons to trigger the release of electrons, which are then transported to create electricity. Photo-reactive materials can be printed or coated inexpensively onto flexible substrates

using roll-to-roll manufacturing, similar to the way newspaper is printed on large rolls. The process is non-toxic and environmentally friendly, and because it’s conducted at low temperatures, it is less energy intensive than other production technologies. The process is five times more affordable than producing traditional solar panels and has the added benefits of being lightweight, versatile and flexible. In the future, we may see large areas of ship structures covered with printable solar cells.

For the storage and transfer of energy, the shipping industry will welcome developments in carbon nanotubes. Unlike copper wires, these hexagonal strand formations are 40,000 times thinner than a human hair. Carbon nanotubes are ideal for use with high voltage power lines. Mechanically strong, yet flexible enough to be knotted or woven together into long lengths of wire, they are capable of carrying about 100,000 amps of current per square centimetre of material – about the same amount as copper wires, but at one sixth of the weight. Carbon nanotubes are able to carry more electricity over longer distances without losing energy to heat – a problem with today’s electrical grid and with computer chips. Since the nanotubes are made of carbon and not metal, they don’t corrode.

Electricity storage, solar cells and carbon nanotubes are existing technologies, but more work is required before they can be applied to the shipping industry. However, it is likely that photovoltaic and battery technology will soon be available to help power hybrid engines, DNV GL forecasts. Also, the industry is likely to adopt reflective coatings for ships operating in temperate climates, which will help to reduce energy consumption and corresponding emissions.