Composite Materials in Railways

Introduction to composites and FRPs

For a composite material to be considered a real composite, it must have two components whose combined strength is greater than that of the sum of their individual components. 1+1 doesn't equal 2 in the world of composites. A composite material can take several forms, such as particleboard, for example (wood and glue).

Figure: FRP Composites

A resin and a structural fiber are the two main components of FRP composite materials. FRP composites employ a wide range of fiber reinforcements. Composites manufacturers have traditionally relied on low-cost glass fiber (fiberglass) as their primary material. The great tensile strength of aramid fiber, such as that found in DuPont's Kevlar trademarked product, makes it excellent for ballistic and impact applications. Its high modulus-to-weight ratio makes it possible to create lightweight and strong structures with carbon fiber, another common reinforcing fiber.

Although various fibers, such as basalt, thermoplastic fibers, natural fibers, and others, are routinely utilized in composites nowadays. They are glass, aramid (a polyamide), and carbon (a carbon-based polymer).

Purely in terms of fibers, they're supple and pliable. Textile weaving and knitting machines, both traditional and updated, are used to weave or sew these fibers together into cloth. To create a strong composite material, these cloths must be saturated with resins before being used. 

Composites are the intended use for the resins. Most resins used in composites are either brittle or overly flexible when used on their own. Thermoset or thermoplastic are the two main types of resins. Composite resins have traditionally been thermoset, although thermoplastic resins are becoming more prevalent.

Polyester, vinyl ester, urethane and phenolic are just a few of the thermoset resins available. There is a chemical reaction that completely links the molecules of these resins before they solidify. The resin will wet out the structural fibers in composites, encasing and curing them.

Curing takes place in a mould, mandrel, or die, giving the completed composite the desired shape and appearance. Even a flat sheet of paper might be used to make it. Once the composite has been cured, the resin and fiber can be selected to produce qualities that are customized to the application's specific needs.

Possible Properties of FRP Composites

·         Lightweight

·         Noncorrosive

·         Fire and flame resistance

·         Toughness / Impact resistance

·         Tailored flex properties

·         Attractive Cosmetics

·         Non-conductive or extremely conductive

·         Water resistance

All across the world, composites have been hailed as a wonder material for the transportation industry. Beyond the benefits of their different mechanical features, composites give train coaches an attractive appearance, particularly when there are few joints, and the material is molded. Assimilability for modular panel type construction adds to the components' maintainability. Due to their non-recyclability, composite materials offer a distinct advantage over metals when it comes to railways in India.

Increasingly, composite materials are being used in the railway industry, where the performance gains can be substantial. Up to 50 percent for structural and 75 percent for non-structural applications bring associated benefits of high-speed, decreased power consumption and lower inertia, as well as the capacity to carry bigger payloads. Structural materials with high rigidity minimize (even eliminate) supporting framework, enhance passenger space, and readily carry fittings. Composites are easy to handle and install, and their modular design allows for quick installation. The system as a whole is protected from fire thanks to its fire-resistant properties.

Passenger coaches rely heavily on composites because of their superior structural qualities and improved looks. Glass fiber reinforced with polyesters/epoxies and phenolic resins is the most common material used in the construction of coaches. The Indian Railways have already started implementing plans to use composite materials, particularly in the cars' seating areas. Higher speeds can only be achieved with lighter coaches in a mass transit system. Until recently, steel and cast iron were replaced by stainless steel and light alloys in the construction of railroad car bodies. GFRP, which resists corrosion and is easy to work with, is becoming more and more common.

The Indian Railways have already identified composites as a promising material for use in their equipment. Composites are being introduced into numerous railway applications by the Research, Designs, and Standards Organization (RDSO) and Integral Coach Factory (ICF). Several carriage components, such as louvre and glass shutters, window sills and frames, toilets, coach interior panels, brake pads, and battery box trays, have already been well developed in FRP composite.

The trains utilize natural fiber thermoset composites for a variety of applications, including the 1.6 mm-thick roof ceilings and floors. The railroads' goal is to completely eliminate the use of wood and plywood in the carriages. In addition to the above, the Indian Railways has started using composites in the following applications: components for coaches like window frames & shutters; a wall protector in toilets; axle box covers for coaches – the latter of which is made of composites; and modular interior panel and partition; luggage bins, toilet modules, bulkheads, interior walls & doors; interior furnishing and seating; and engine room sound attenuation.

An additional number of components will be replaced with composites by the RDSO in the near future. In addition to the FRP gear case for locomotives (a weight savings of 372 kg per six-axle system), axle box covers, brake-gear bushings, berth and chair backings, roof water tanks, lavatory chutes, window guides, doors (main entrance, sliding door for first class AC compartment, inter-communication door in AC coaches), folding tables, fuel injection pump cover, luggage racks, etc.,

Figure: Lightweight composites for railway

As per the ICF General Manager Sudhanshu Mani, “The interiors of the Train 18, developed indigenously by the Integral Coach Factory (ICF) have been made up of composite materials, which are fire resistant,” 

The next step in the project's evolution will be the production of FRP sliding doors for carriage restrooms. It has been possible to make two alternative doors, one with a 'compreg' interior and FRP skins on both sides, and the other sandwich structure with FRP external skins and PU foam in the middle. The results of RRL-extensive Bhopal's testing were quite favourable.

The use of composites is likely to increase dramatically with the introduction of new coaches on the Indian Railways, and local suppliers will have high expectations for components with the highest possible quality. When it comes to bringing in cutting-edge composite fabrication technology and experience to the United States, this is an urgent need.

The development of innovative thermoset and thermoplastic composite goods would go a long way in generating new application areas and therefore extending its market reach. India can surely carve out a role in the upcoming technology of composite fabrication with its great knowledge base in diverse resins, catalysts, and curing systems, as well as its ample supply of various raw materials. Because the composites industry relies heavily on human labour, having enough highly trained workers available in the country would be an asset to its growth.

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