Considerations when selecting composites for aerospace and defense

As the aerospace and defense industries continue to push toward higher temperatures, lower weights, and more demanding mission profiles, more composite materials are emerging to advance thermal and structural design, enabling technologies that were previously not feasible with metal-based systems alone. In this article, we cover different types of composites commonly used and selection considerations for future designs.

Composites used in aerospace and defense

Let’s first take a look at commonly used composites and how engineers use them in aircraft design and defense applications.

Carbon fiber reinforced polymers

Carbon fiber reinforced polymers (CFRPs) continue growing in popularity due to their strength-to-weight ratio, fatigue resistance, and design versatility. These composites are typically lighter and stronger than aluminum, giving engineers design flexibility that metals cannot.

In commercial aviation, engineers use CFRPs in fuselage panels, wings, tail sections, and engine nacelles. The Boeing 787 Dreamliner fuselage, shown in the video below, is an example of CFRP’s value, resulting in a 20% weight reduction compared to conventional aluminum designs while improving fatigue and corrosion resistance. Military aircraft, including the F-22 Raptor and F-35 Lightning II, have CFRPs in skin panels, internal structures, control surfaces, and stealth-enhancing shapes, which reduce radar cross-section while boosting fuel efficiency and range.

The Boeing 787 Dreamliner airframe uses 50% composites by weight, reducing fuel consumption. Video source: Boeing

Beyond airframes, engineers use CFRPs in rotorcraft blades, UAVs, missile bodies, and satellite structures, where reducing mass directly improves performance, endurance, and payload capacity. Defense teams also use CFRPs for soldier protection gear, radar systems, and lightweight armored vehicle components, taking advantage of their strength, stiffness, and energy absorption characteristics.

Some high-performance carbon fibers have tensile strengths greater than 7 GPa (several times stronger than steel) with elastic moduli up to 350 GPa, depending on the fiber grade and manufacturing process. When combined with advanced epoxy resins, the resulting composite materials (called prepregs) can achieve very high strength-to-weight ratios.

The composite’s fiber orientation and layup sequence impact the material’s mechanical properties and performance. For example, stacking layers in different directions — such as 0°, ±45°, and 90° — creates a quasi-isotropic laminate, which balances strength and stiffness in all in-plane directions. Contrarily, laying all fibers in the same direction (unidirectional layup) provides maximum strength along a specific axis, which is suitable for parts that carry loads in one direction.

Ceramic matrix composites

Ceramic matrix composites (CMCs) are high-temperature materials engineered to overcome the brittleness of traditional ceramics while operating in extreme thermal and oxidative environments. CMCs consist of a ceramic fiber reinforcement, such as silicon carbide (SiC) or alumina (Al₂O₃), embedded in a ceramic matrix. Such materials maintain structural integrity and low density at high-temperature applications above 2,192° F (1,200° C) without requiring active cooling or heavy metallic heat shields. They are an attractive solution for lightweighting in propulsion and thermal protection systems, as they are resistant to oxidation, thermal shock, corrosion, and creep, even in chemically aggressive environments.

In aerospace, CMCs are primarily used in gas turbine engines, especially in components exposed to extreme heat, such as turbine shrouds and vanes, combustor liners and nozzles, exhaust components, and thermal barrier systems in aircraft and spacecraft. The defense sector is exploring and using CMCs in hypersonic vehicles, missile systems, and thermal protection structures, all of which experience prolonged exposure to extreme heat and aerodynamic loading. They are also being evaluated for use in rocket nozzles, scramjet liners, and next-gen reentry vehicles where conventional metals would fail or require excessive insulation.

Metal matrix composites

Metal matrix composites (MMCs) provide a middle ground between conventional metals and full composite materials. For example, aluminum reinforced with silicon carbide particles or carbon fibers improves stiffness and thermal properties. Such materials excel in applications that require dimensional stability across a wide range of temperatures, such as precision optical mounts and satellite structures.

MMCs are used in airframe structures, particularly aluminum-based composites reinforced with silicon carbide or boron fibers. These materials provide improved strength-to-weight ratios compared to traditional aluminum alloys, enabling lighter aircraft with maintained or improved structural integrity. Wing spars, fuselage frames, and landing gear components can also incorporate MMCs. In jet engine applications, titanium and aluminum matrix composites reinforced with ceramic fibers are used in compressor blades, turbine discs, and combustion chamber components.

In the defense sector, MMCs play crucial roles in rocket and missile propulsion systems. Beryllium-aluminum composites are used in lightweight structural components for space vehicles, while tungsten-based MMCs are used in rocket nozzles and thrust chambers for extreme heat resistance. In military electronics and avionics, MMCs provide reliable thermal management properties. Additionally, aluminum-silicon carbide composites are used for heat sinks and electronic housings in radar systems, satellite components, and military communication equipment, effectively dissipating heat while maintaining electromagnetic shielding.

Considerations for selecting composites in aerospace and defense applications

Engineers face complex considerations when selecting composite materials for aerospace and defense designs. Here is an overview of key factors that significantly influence a system’s cost, manufacturability, performance, and long-term viability based on composite type.

CFRP considerations

• Manufacturing CFRPs can involve complex layup processes and autoclave curing that require skilled labor and quality control challenges with void detection and consistent fiber orientation. However, significant advances in out-of-autoclave processing, automated fiber placement, and resin transfer molding are increasingly common and reduce costs.
• Cost considerations include high raw material costs and labor-intensive manufacturing, though these are often offset by potential lifecycle savings through weight reduction and corrosion resistance, as production volumes increase.
• Environmental and durability concerns include susceptibility to UV degradation and moisture absorption, with impact damage potentially causing internal delamination that is difficult to detect and repair.
• Design and integration challenges arise from anisotropic properties that require careful fiber orientation design, complex joining methods since welding isn’t possible, and thermal expansion mismatches when interfacing with metal components.
• Certification and qualification hurdles involve extensive testing to characterize anisotropic properties and long-term environmental effects, with regulatory agencies requiring comprehensive damage tolerance and repairability demonstrations.
• End-of-life management remains challenging due to thermoset matrix systems. Though pyrolysis and solvolysis techniques provide fiber recovery, they are not widely implemented, and incineration for energy recovery is currently the more common disposal option.

CMC considerations

• Manufacturing CMCs requires ultra-high temperature processing (greater than 1,000° C) with specialized furnaces and controlled atmospheres, limited manufacturing scalability, and challenges in achieving consistent microstructures in complex geometries.
• Extremely high initial costs come from expensive ceramic fibers and complex processing, but these are justified in critical high-temperature applications where performance requirements outweigh costs.
• Environmental and durability concerns include the potential for fiber-matrix interface degradation over extended service life in extreme environments.
• Design and integration challenges include limited ductility and notch sensitivity that require stress concentration avoidance in design, while thermal expansion matching with surrounding components presents significant engineering challenges.
• Certification and qualification are complicated by the limited availability of long-term service data, which necessitates extensive qualification programs. Additionally, establishing inspection and maintenance protocols for new material systems poses regulatory challenges.
• End-of-life management offers potential for high-value material recovery due to expensive ceramic constituents. However, separation and purification processes are complex and energy-intensive, requiring the development of specialized recycling infrastructure.

MMC considerations

• Manufacturing MMCs requires careful control of matrix-reinforcement interfaces to prevent unwanted chemical reactions and to ensure uniform reinforcement distribution.
• Cost considerations involve moderate to high material costs depending on reinforcement type and processing method, but they can provide better cost-performance ratios than CFRPs for specific applications.
• Environmental and durability concerns include galvanic corrosion risks from dissimilar materials that require careful material selection and protective coatings.
• Design and integration challenges include potential machining difficulties and potential for reinforcement damage during secondary operations.
• Certification and qualification programs must address processing variability and long-term property stability, with particular focus on interface integrity and potential for reinforcement-matrix interactions over service life.
• End-of-life management is generally favorable since metal matrix components can often be recycled through conventional processes. Though reinforcement separation may be required depending on the application, making them generally more recyclable than polymer matrix composites.

Summary

In summary, selecting composite materials for aerospace and defense applications requires careful consideration of the operational environment, performance requirements, and manufacturing constraints unique to each mission profile. While CFRPs remain the go-to material for building weight-reduced structures subject to moderate temperatures, CMCs are useful for turbine hot sections and hypersonic applications that experience excessively high temperatures. MMCs, though less prevalent in commercial aviation, are suitable for rocket propulsion systems, precision instruments, and applications demanding tailored thermal expansion characteristics. As additive manufacturing techniques mature and material costs decline, aerospace engineers will likely leverage hybrid approaches that align material capabilities, performance requirements, supply chain maturity, and costs.

Looking for more in-depth guidance on aerospace and defense applications? Download our Special Report: Design Tips For Aerospace & Defense OEM Engineers.

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Filed Under: Aerospace + defense, Materials • advanced

 

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