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For many years, carbon-fiber composites have been the materials of focus for the design and manufacture of aircraft and aerospace components. While they have received success and widespread adoption, a new breed of materials has begun to disrupt the sector.
Reinforced polymers have entered the aerospace industry, with engineers developing their use, which has resulted in drastically changing how aircraft are designed and built. The interest in reinforced polymers continues to gain traction, with NASA recently investing $15 million into the development of next-generation materials for use in deep space missions.
Below, the ways in which reinforced polymers are being used in aerospace assembly will be discussed, as well as what the future of the market looks like.
The Growing Use of Reinforced Polymers in Aerospace
Recently, the use of traditional plastics has become widely adopted in the design and manufacture of aircraft. While aluminum was once the focus of this industry due to being low-cost, lightweight, as well as corrosion and fatigue resistant, aluminum is beginning to be replaced by polymers, especially in the production of structural components of the aircraft.
Acrylonitrile butadiene styrene, polyphenylene sulfide, and polyetheretherketone (PEEK) are polymers that have already been established within a number of applications. In addition, the aerospace industry has particularly focused on developing the use of polyetherimide for the production of a range of parts because it is able to produce components while meeting the flame, smoke, and toxicity requirements laid out by the FAA.
Polyetherketoneketone (PEKK), a high-temperature engineering polymer with desirable mechanical properties, thermal stability, chemical resistance, and flame retardancy has also become a competitive alternative to aluminum.
Plastic is already used to create a number of interior components such as air ducts, floor panels, cabin partitions, overhead luggage bins, avionics sensor plates, ventilation impeller blades, and electronic component mounting brackets. Polymers are also being used to create structural components such as wing ribs and spars, as well as external components such as fuel tank covers, pylon fairings, landing gear hubcaps, and radomes.
Engineers are continuing to work with polymers to explore their full potential for use as aerospace materials. Because of their numerous advantages over traditional aluminum, including being strong, lightweight, and durable, plastics may be able to replace aluminum in other areas of aerospace assembly.
One way in which these plastics are already transforming the assembly of aircraft is that PEEK plastics are replacing metal fasteners and screws because of their noncorrosive properties. These plastic components can act as direct replacements because their use does not require changes to the aircraft’s overall design.
Because of their thermal and mechanical stability, zero flammability, low outgassing in a vacuum, and insulation properties, polymers have the potential to replace metals in various other areas of aerospace assembly.
Research is leading to more new plastics being created each year to replace the metals used in aircraft construction. Plastics have many advantages that make them suitable for use in aerospace applications, and these advantages often make them a better choice than metals.
Their weight-to-strength ratio, corrosion resistance, and the ability to produce them in small quantities make plastic ideal to use for producing aircraft components. Plastic parts are also self-lubricating and, therefore, reduce the risk of fire and explosions. Plastics are being developed that overcome the load-bearing, torque handling, and gear drive limitations of previous technologies.
A substantial trend in the use of plastics in the aerospace sector is in replacing traditional metallic structures with carbon-fiber-reinforced thermosetting polymer composites. The aim of this transition has been to reduce the weight of the aircraft by constructing its components from lighter materials, and, therefore, saving on fuel costs. Significant amounts of research are currently underway exploring the use of thermoplastic carbon-fiber composites. Much of this work is based on PEEK, with the aim of increasing manufacturing productivity and building aircraft at greater speeds.
The next two decades are expected to see the launch of 35,000 new aircraft. With such a high expected production volume, the adoption of thermoplastic composites will be more important than ever in solving the cost and weight challenges posing the industry.
Self-Healing Carbon Fiber Reinforced Polymer
Recently, advances have been made in the development of carbon fiber reinforced polymers with self-healing properties that overcome the effects of damage in composite materials, which is particularly important in aircraft design and assembly.
Engineers have been able to reduce the vulnerability of aircraft components to impact damage. Research has demonstrated that particular fiber spacings and polymer combinations are especially effective at producing minimal degradation in flexural strength and ply disruption, giving carbon fiber-reinforced polymers their self-healing characteristics.
Overcoming the Limitations of Reinforced Polymers
There are some limitations, however, to adopting the use of reinforced polymers in the aerospace sector. For example, polymer composite panels are harder to manufacture in comparison to those made of aluminum, which makes their manufacture more expensive. There is also a reluctance to switch from aluminum to reinforced polymers by engineers who have been working with aluminum for long periods as they have developed expertise and trust in the material.
In addition, reinforced polymers still face problems in drilling. When holes are drilled into fiber-reinforced polymer composites for rivets and bolts to join parts, it weakens the strength of the material, leading to part rejection at the assembly stage.
The use of polymer composites is currently in its earlier stages, and there is still much to be learned about how they behave under a variety of conditions. The impact of long-term aging due to moisture, ultraviolet radiation, and elevated temperatures, for example, is still not fully known and needs to be explored further. Gaining deeper insights into the behavior of reinforced polymers will give engineers the confidence they need to fully adopt this material and to recognize its full potential in the aerospace industry.
References and Further Reading
Aamir, M., Tolouei-Rad, M., Giasin, K., and Nosrati, A. (2019). Recent advances in drilling of carbon fiber–reinforced polymers for aerospace applications: a review. The International Journal of Advanced Manufacturing Technology, 105(5-6), pp.2289-2308. https://link.springer.com/article/10.1007/s00170-019-04348-z
The Growing Role of Plastics in Aerospace Assembly. Available at: https://www.assemblymag.com/articles/94125-the-growing-role-of-plastics-in-aerospace-assembly
Williams, G., Trask, R. and Bond, I. (2007). A self-healing carbon fibre reinforced polymer for aerospace applications. Composites Part A: Applied Science and Manufacturing, 38(6), pp.1525-1532. https://www.sciencedirect.com/science/article/pii/S1359835X07000152