By Girish Linganna
Composite material refers to a continuous heterogeneous material comprising two or more components. Reinforcing elements that provide the necessary mechanical characteristics of the material and a matrix (or binder) that ensures the joint operation of the reinforcing elements can be distinguished within the composite material.
Choosing the initial parts well and the technique used to put them together affects the material’s efficiency and performance. This is done using a technology that creates a strong bond between the parts while keeping their original properties.
In particular, interfaces between the reinforcing elements and the matrix are essential for ensuring that the likelihood of the material cracking is low. Also, unlike metals, an increase in static strength usually leads to increased fracture toughness in composites.
Note that composites can be made of both natural and artificial materials. For example, wood is a natural composite of cellulose, wood fibres, and lignin. Lignin is the natural glue that holds wood fibres together and keeps them stable; the latter provides wood its strength. Other composites, like plywood, are synthetic- made of both natural and artificial materials.
Composites can be associated with many daily necessities ranging from elements of aircraft, boats, sporting equipment, automotive components, and wind turbine blades to body armour, building materials, water pipes, bridges, tool handles, ladder rails and more.
Master Of One, Not Jack Of All
While composites are quite helpful, one must remember that they are made for specific tasks and can not provide every possible benefit. However, when designing a new composite, an engineer is free to give it features that are much better than traditional materials. This is true when it comes to achieving a particular goal in a given mechanism. While the composite could be better than conventional materials in some aspects, it could be worse in others. This means that composites can not be better than traditional materials in every way. The engineer does all the necessary calculations for each product and then chooses the best material for production.
DRDO laboratories stationed in Pune, Hyderabad, and Bengaluru have been practising forming composites for over 20 years. ISRO, CSIR, and DRDO labs were the first to set up manufacturing processes and industries for product development. These labs worked on products related to aerospace. As part of this effort, the army is building bridges with carbon fibre reinforcements that are 40% lighter than their metal counterparts. Armoured vehicles with hulls made of glass fibre and ceramic armour have also been made.
COVID-19 & Its Impact On Composites Delivery
It is quite feasible to replace traditional materials with composites. The latter is making the process of designing easier and the final products in a wide range of industries- from aerospace to clean energy- much better. Composites are becoming a vital part of the Aerospace and Defence (A&D) sector because they are reliable and easy to use.
However, recent challenges have caused delays in making defence equipment that heavily uses composites. This is especially true when the COVID-19 pandemic has caused a rise in import and breakdown of supply chains for specialised military materials. The cost of shipping has gone up. Most raw materials for composites need to be transported and stored in 20°C freezers. Most composites also have expiration dates. If they are not used in time, one could lose a lot of money.
Still, since the benefits of using these materials outweigh their risks, composites have found multiple applications.
Applications In India
Composites are used in a lot of Indian weapons programmes right now. Some examples are the airframe of the LCA, the superstructure of naval ships, and parts of both strategic and non-strategic missile systems.
Multifunctional composites are used for armour. In the aerospace industry, composites with properties like radar transparency, stealth, etc., are being made from scratch. R&DE (E) in Pune made the first composite sonar dome built indigenously in India.
Composite materials have been used for a long time in the marine industry to make gratings, ducts, shafts, pipes, hull shells, etc. Wood and ferro-cement are two other types of composites that are still used for marine purposes.
In the last few years, scientists have learned much more about how composite materials work and how to make structures that work well in the sea. Processing and manufacturing have also gotten more attention. This implies that building complex, large assemblies that can hold heavy loads may be possible. However, boats, ships, and other marine objects made from composites must make the most of their capital and operating costs to use composite materials viably.
Marine composites provide advantages such as high strength and low weight. In addition, they are corrosion-resistant and simple to fix (thus saving money on repairs). Since their flexibility is customisable, making structures with complicated shapes and geometry using composites is not hard compared to traditional materials.
However, they are also punctuated by weaknesses such as low impact resistance, reduced heat resistance among some composites, and lower resistance to UV rays. Additionally, they cost more than some traditional materials at conception.
Ferro-cement, glass-reinforced plastic, wood/adhesive composites, aramid fibre composites, and carbon fibre are some common marine composites.
Ferro-cement: This is likely the oldest composite material used in the marine industry. It was used to make low-cost barges. A steel frame made of reinforcing rods and chicken wire is used as a “template” for the hull. Cement is poured around the template to form the hull. Then, it is covered using ferro-cement and left to dry. Even though it is a cheap composite, its armature corrosion is a common problem in marine environments that are chemically aggressive. But ferro boats are still used by some people today.
Glass-reinforced plastic: Just after the invention of polyester resins came the glass fibres. Soon, people started making boats out of glass-reinforced plastic. These boats have been around since the early 1950s and are still a big part of Marine composite construction today.
Wood/Adhesive Composites: War requirements pushed people to come up with the “hot moulded” and “cold moulded” methods of building boats by laying thin pieces of wood over a frame. On the other hand, many high-performance adhesives based on urea have been made for moulding boat hulls and making aeroplanes. This helps speed up production and lessens the need for aluminium and steel.
Aramid Fibre Composites: They are often used to strengthen parts of sailing yachts like the keel and bow. Aramid Fibre composites are also better at absorbing shock, which makes them perfect for ocean racing.
Bennington-based Fothergill Composites Inc. has made a safety cell cockpit out of carbon and aramid fibres with an aramid honeycomb core to protect the driver in any situation, especially in a high-speed crash. This structure can survive a 100-foot drop without significant damage.
Carbon fibre: These are increasingly being used in sailboats, superyacht furniture, and high-strength interior mouldings because they help keep the boat stable and perform well while being light. Carbon fibre is also seen as a trendy material. It is often used instead of woven materials that have better material properties or look better.
Carbon fibre reinforced epoxy composites are increasingly being used in honeycomb or foam-covered boat hulls, structural frames, keels, masts, poles, booms, and even carbon winch drums and shafting. Using composites can help improve performance and reduce the chance of a boat breaking down in harsh sailing conditions. More than any other marine structures, racing yachts use advanced polymer composites to save weight and make them last longer.
Bright Path Ahead
Materials science and composite technology are making fast progress, and new composites like epoxy mixtures that use carbon nanotubes are becoming more popular as the need for high-performance marine structures grows.
Composites are very important in marine applications because they are light, easy to make, durable, and strong. Composite materials will play a big role in the future of Marine construction as the Marine industry continues to look for ways to be more efficient and cut costs overall.
Girish Linganna is an Aerospace and Defence Analyst & Director ADD Engineering Components (India) Pvt Ltd.