Thermoplastic Composites Taking-off into a Clearer Future
Composites have had an incredible story from being just 4% in 1970s to having more than 50% share in aircraft structural weight now. Known for its demanding requirements, the aerospace industry has driven significant advancements in material science. In recent years, the spotlight has turned to thermoplastic composites (TPCs). During 2024-2030, the A&D industry is projected to generate a cumulative demand of ~27 million lbs. for thermoplastic composites.
Published: 11 Sep 2024
In
early 2024, production of the world’s largest thermoplastic composite aircraft
fuselage segment was successfully completed by welding two 8-meter-long CFRP (Carbon fiber reinforced plastics)
half-shelf. This feat was achieved under the aegis of EU-funded Clean Sky
2/Clean Aviation project ‘Large Passenger Aircraft’ (LPA) by the Fraunhofer- Gesellschaft in Stade, Germany, together
with international project partners, which joined together a true-to-scale
upper and lower shell of the ‘Multi-Functional Fuselage Demonstrator’ (‘MFFD’) using automated positioning and
joining processes.The
almost rivet-less structure and the automated pre-integration resulted in 10% savings on each, weight, and cost.Another
interesting EU-funded project is the DOMMINIO
project (Digital Method for Improved Manufacturing of Next-generation
MultIfuNctIOnal airframe parts) which aims to demonstrate technologies enabling multifunctional,
intelligent airframe parts that would also have benefits in repair and
recycling at the end of life (EOL). The project bets on thermoplastic
composites using Toray Advanced Composites TC 1225 unidirectional (UD) tape
comprising carbon fiber and LM PAEK polymer by Victrex.There
are more such projects where prominent companies in the aerospace and
composites industries have joined forces to promote thermoplastic composites and
bring them into the mainstream.Known
for its demanding requirements, the aerospace industry has driven significant
advancements in material science. In recent years, the spotlight has turned to thermoplastic
composites (TPCs), a material class that has the potential to revolutionize
the way we approach aircraft system design. The
Impressive Story of Composites in Aerospace & Defense (A&D)Composites
have had an incredible story from being just 4% in 1970s to having more than 50% share in structural weight now. From A300 to A350XWB for
Airbus, and from 757/767 to 787 for Boeing, the composites usage has taken a
big leap, now accounting for 53% of the material mix of A350XWB and 50% of 787.
(Check Figure.1. for composites usage trends in different
aircraft programs)The
usage of composites in aircraft, however, can be traced back to the World War I
& II eras with notable examples like ‘the flying boat’ and ‘the Mistel
(mistletoe)’. However, specific details on the type and quantity of composites
used in these aircraft are limited.It
was also noted that Glass fiber reinforced plastic (GFRP) was the composite
structural material used in a wide range of aircraft and missile applications
between the 1940s and 1960s. According to the Defense Technical
Information Center (DTIC), the A-1E was the first production aircraft
to incorporate composite GFRP. Grumman Aircraft produced fiberglass
vertical tail structures for this military aircraft. This occurred
during the mid-1960s when another breakthrough - ‘Boron fiber reinforcement’
was introduced to the A & D industry.During
the 1970s, metals like aluminum, steel, and titanium dominated the aerospace
manufacturing industry, comprising ~70% of the average aircraft’s structure.
In contrast, the share of composites was infinitesimal, accounting for
just 4% of materials used in aircraft manufacturing.The
benefits of composites were numerous, and impressive, but there wasn’t any rush
in adapting composites in this industry. Gradually, after a lot of research and
analyzing the long-term benefits of composites, the industry embarked upon the
usage of composite materials.In
the early 2000s, the Boeing 787 Dreamliner broke new ground
as the world’s first major commercial airliner to feature a primary airframe
constructed from composite material. The aircraft is notable for its
extensive use of composite materials, comprising ~80% of its volume and 50% (that
is approximately 32,000 kgs of carbon fiber reinforced composite) of
its total weight. Each Boeing 787 aircraft then used composites for wings,
tails, doors, fuselage, and interior.Not
just Boeing, but other aviation giants like Bombardier, BAE systems, Raytheon,
Lockheed Martin, and GE Aviation gradually jumped on the bandwagon of using
composites in their aircraft.
Figure1: Composites Usage Penetration Trend in Different Aircraft Programs Evolution
of Thermoplastic CompositesThroughout
this transition, thermoset composites and autoclave processing have been
the predominant choices for manufacturing aircraft components. Since the outset
of this century, out of autoclave (OOA) processing techniques have begun
attracting interest owing to the possibilities of faster production and lower
fabrication costs, which is the industry’s priority. Owing to their properties,
the surge in interest in OOA paved the way for the adoption of new materials - thermoplastic
composites - which are well-suited to these processing methods.Applications
of thermoplastic composites date back to the US military’s F-22 jet fighter’s
landing-gear and weapons-bay doors in the 1980s, and the outer wing trailing
edge skin panel or shroud for the Fokker 50 passenger aircraft in the 1990s.
(Check the evolution of TPCs in Figure.2.)Figure
2: Evolution of TPCsToday,
most of the modern aircraft feature thermoplastic composites in several
applications, such as clips, cleats, fixed-wing leading edges, J-nose leading
edges, panels for fuselage, profiles & brackets, ribs & angle brackets,
control surface parts, seat backs, window panels, and cockpit floor.Clips
and cleats are considered to be the largest applications of thermoplastic
composites in the industry and are made from carbon fibers with either PPS or
PEEK resins. There are about 8,000 clips and cleats used in each A350XWB and
about 10,000-15,000 clips and cleats in a B787 aircraft.
Figure 3: Key Applications of Thermoplastic
Composites in an Aircraft Thermoplastics
Vs ThermosetsCurrently,
thermoset composites dominate the A&D composites market; however,
thermoplastic composites are successful in marking their presence in the
structural sections of an aircraft by replacing both thermoset composites as
well as traditional metals.Unlike
their thermoset counterparts, thermoplastics are capable of being reheated and
reshaped repeatedly without losing their structural integrity. Known as thermoplasticity,
this unique property enhances thermoplastic composites’ recyclability.Here’s
a quick rundown of the differences between ‘thermosets’ and ‘thermoplastics’ -
Properties
Thermosets
Thermoplastics
Viscosity
Low
High
Chemical
Resistance
High
Moderate
Toughness
Moderate
High
Age
(Shelf life)
Moderate
Infinite
Reusability
(Thermoformable)
Low
High
Cost
Medium
High
Melting
Point
High
Low
Molecular
Weight
High
Low
Overall
Cost Savings
Low
High
Table 1: Property Comparison of Thermosets & Thermoplastics Owing
to their many benefits, thermoplastic composite materials in the A&D
industry are witnessing an illustrious journey. Valued at US$ 330 million in
2023, the global aerospace thermoplastic
composites industry is
expected to reach US$ 870 million in
2030, growing at a skyrocketing annual growth of >14%.It
is important to note that the above figure represents only a fraction of the overall
composite usage in the A&D industry. Despite the impressive growth,
thermoplastic composites (TPCs) still account for merely 2% of total
composites usage in the A&D industry which is around 34.5 million pounds.Once
considered unsafe for even structural components, TPCs are now being applied
to critical control surfaces too.
Figure
4: Thermoplastic Composites Contribution in the A&D Composites Market in
2023 (Volume)
