Turkish Aerospace

Fahrettin Ozturk

Composite materials have got great attention over metals in recent years especially in aerospace industry due to their high strength to weight ratio. In general, they are made of thermoset resin reinforced with stronger and stiffer fibers. As of today, considerable amount of knowledge and processing methods have been developed for thermosets composite materials. However, there are several limiting factors and difficulties for these types of materials. While difficulties in repairing damaged parts can be shown as a limiting factor, at the same time recycling of faulty products prevents them from achieving the status of an environmental friendly material. Therefore, researchers have been working on the development of alternative greener resin materials. In this context, the composite materials market has recently been focusing on thermoplastic composites (TP) due to their easy use and recyclability potentials. It is clear that, without any doubt, the biggest role in the development of this market is aerospace industry. On the other hand, fossil fuels and their effects on the environment are forcing regulators to find new solutions to keep our world safe. For this reason, there have been an intense effort for more environmentally beneficial products by reducing carbon emissions both in production and products. Considering that electric aircrafts and automobiles are becoming more and more common today, there are an increasing trend in using composite materials in main structures, since weight reduction is one of the priority key issues to improve the fuel consumption performance of vehicles. In this context, composite materials come to mind when an environmentalist solution is sought, especially in terms of lightness, which has been considered in aerospace industry for years. According to the published data, it can be seen that the investments to be made for the future, especially in the aerospace industry are increasing rapidly. For example, based on BOEING’s market analysis, it is predicted that a total of 38 thousand new aircraft will be needed as regional jet, single/double aisle passenger aircraft and wide body aircraft between 2015-2034 years (Ref 1).

It is clear that thermoplastic composites (TP) are candidates to replace polymeric composites with thermoset resins, which are used extensively in the aerospace industry. They have been a great effort in the development of this material both in the academia and industry. The developed candidate materials are PPS, PEEK, PEKK, LM-PAEK, which can tolerate high temperatures and are advantageous in terms of high strength to weight ratio. Technological developments show us that these materials can be used in parts that are exposed to structural loads in the near future. It is expected that these materials have become widespread in aerospace and also in other sectors. Manufacturing methods have been studied to reduce the production time of parts, which is also an important aspect of environmentally friendly Product Life Cycle (LCA). New companies have emerged in production-oriented issues such as (TPSF) , Automated Fiber Placement (AFP) , Thermoplastic Additive Manufacturing (TPAM) , etc., and studies in this area have gained momentum.

"Thermoplastic composites (TP) are candidates to replace polymeric composites with thermoset resins, which are used extensively in the aerospace industry. They have been a great effort inthe development of this material both in the academia and industry"

All the advantages of thermoplastics are important driving factor and motivation source in concentrating on this technology, such as being suitable for rapid production, being recyclable, reshaped and repairable, and of low thermal conductivity. Also academia and industry take advantage of these advantages to make many product-specific improvements. Of course, in addition to the advantages of thermoplastic composites as a product on a detail basis, when a product consisting of more than one piece is considered, its compatibility with similar and dissimilar materials is a critical issue that should be emphasized. Since systems such as automotive or aircraft are composed of many sub-components which are made of different materials, it is of great importance that parts made of thermoplastic materials are assembled seamlessly and accurately into parts made of other similar or dissimilar materials. It is vital that the relevant assemblies can also withstand external influences such as temperature and forces on the system. For example, it is compatible with metal surfaces when combined with both bonding and welding methods.

Despite all its advantages, the most important drawback of TP known for now is that it is a much more expensive material than thermosets. An improvement is expected here as such materials are used even more widely in industrial applications. However, as mentioned above, the easy compensation of the lines encountered during the production phase and the ability to reproduce the related parts up to a certain level will significantly affect the costs and, contrary to popular belief, the cost loss will be even less. Another important technical disadvantage compared to thermoset composites (TS) is that they soften when heated. This can impose restrictions on application areas.

It is obvious that the increasing number of scientific publications in the current researches carried out to take the properties of thermoplastic materials one step further. For example, their physical properties are significantly improved by combining them with nano materials. Different forms of nano additives are added to thermoplastics for thermal management, electrical conductivity, structural health monitoring, and higher structural strength. Therefore, the commercialization of these studies will have a multiplier effect on the increase in the use of the material in the future.

It is not known yet that if TP composites can completely replace TS composites in the future, but definitely there will be a significant change.