The Importance of Composite Materials in Aerospace and Defense

Industry Information|

Since man first took to the air, aerospace engineers have concentrated on improving lift to weight ratios of aircraft. The goal has been to design and produce more powerful engines but, overall, lighter aircraft. For this reason, composite materials in Aerospace and Defense (A&D) have become a critical element in the industry.

A composite is a material created from two or more materials with different physical or chemical properties that, when combined, are stronger together than as individual materials by themselves. The component materials do not entirely blend or lose their unique properties but instead reinforce each other’s valuable and powerful traits to improve the outcome or end product. Usually, the engineers determine the resulting composite’s properties based on the anticipated application.

The A&D sector is one of the most regulated industries in the world. Any materials used are also subject to high regulatory and performance standards to ensure they meet the strict demands of the situation they are used in. Composite was up to the mark because of its high strength-to-weight ratio, crucial for aircraft design. It has been used in the aerospace and defense industry for a long time but with limited application. The first conspicuous use of aerospace composites was on a military craft, and this facilitated substantial weight reduction. In 2011 this extended to commercial service with Boeing’s introduction of the 787 Dreamliner model, which was stated to be made of 80% composites by volume.

Other advantages of using composite in aerospace and defense include:

  • They provide higher strength at a lower weight
  • High thermal stability
  • Improved impact resistance
  • Resistance to fatigue and corrosion
  • Complex design capabilities
  • Composite materials are also easier to assemble, which makes the manufacturing process more efficient and less costly.

Types of Composite Materials

Today, nearly half of all the parts in newly built aircraft are made from composite materials. Investments in material development and design help continually improve composites’ application while introducing new options for the aerospace and defense industry. Common types of composite materials include:

Fiber-Reinforced Polymers (FRP)

These are composite materials consisting of solid fibers embedded in a resin matrix. Fibers are necessary to provide strength and stiffness to the composite and generally carry most applied loads. Conversely, the matrix offers bond and protection to the fibers while allowing for stress transfer from fiber to fiber through shear stresses. The fiber determines the strength of the composite, and the composite is named after the fiber. Popular fibers include glass, carbon, and aramid, while matrices commonly used include epoxy and vinyl ester.

There are several types of FRP composites with the three most popular being glass fiber-reinforced polymers, carbon fiber-reinforced polymers, and aramid fiber-reinforced polymers. These polymers have a low density and are preferred in structural applications to replace more conventional materials like aluminum, steel, and alloys to produce lighter products. They are also low maintenance, strong and durable.

Metal Matrix Composites (MMC)

MMCs are engineered combinations of two or more materials, one metal and the other typically a ceramic or organic compound. Polymers consisting of three materials and including more than one metal are called hybrid compounds. Desirable attributes associated with MMCs include increased specific strength, stiffness, wear resistance, high-temperature performance, corrosion resistance, and thermal and mechanical fatigue resistance.

Metal matrix composites usually use three reinforcements: particulate, fibrous and continuous. They are becoming increasingly essential in aerospace and defense due to their improved physical properties, including excellent specific performance. In addition, the materials can directly influence performance benefits such as energy savings and extended component life.

Ceramic Matrix Composites (CMC)

Ceramic matrix composites are engineered with ceramics serving as reinforcement and matrix material. In some cases, the same ceramic is used for both parts of the structure, and additional secondary fibers may be included. Typical reinforcement fibers in CMCs include carbon, silicon carbide, alumina, and mullite and can take different forms, including the more traditional continuous fiber or short fibers, particles, whiskers, and nanofibers.

Ceramic matrix composites behave differently from conventional ceramics and are much better than high-performance metal alloys. Like ceramics, they are rigid and stable at higher temperatures but are also very lightweight and possess significantly more excellent fracture toughness and thermal shock resistance.

Composite Materials Manufacturing Techniques

Aerospace and defense industries use different composite fabrication methods depending on the intended application and required benefits. Some of the most popular composite manufacturing techniques include:

Hand lay-up

This is the most basic composite manufacturing method. It involves laying pre-impregnated piles onto a tool by hand to form a laminate stack. Once the lay-up is complete, the resin is applied to the layer of plies. A variation of the hand lay-up is the wet lay-up, which involves coating each ply with resin before layering them together.

Resin Transfer Molding (RTM)

This is achieved by putting dry reinforcement into a mold and then pumping a mixture of resin and catalyst under low pressure. The pressure is maintained until all the resin cures, and the part is removed. The process is suitable for complex and highly loaded components.

Vacuum Infusion

Vacuum infusion unlike other composite manufacturing methods does not require the use of heat or pressure. The vacuum causes low-viscosity resin to permeate a fibrous preform. This process is suited for large making large components such as boat hulls and wind turbines as it is inexpensive, and the tooling does not have to carry substantial loads during the process.

Autoclave Curing

This method combines vacuum and external pressure to ensure an optimal final product. The vacuum removes air and volatiles trapped within a laminate while the external pressure suppresses any vapors into the resin matrix to avoid the formation of voids. The cure pressure also consolidates the plies to yield high-quality parts.

Composite Materials Applications in Aerospace and Defense

Airplanes and Helicopters

Commercial airplanes like the Boeing 777 weigh about 20% of composites. Components like horizontal stabilizers, wing fairings, engine fairings, vertical fans, and passenger floor beans use composite materials. Composites are also used to make helicopters with the perfect strength from weight ratio. For example, the modern v22 tilt-rotor aircraft relies on composites for its structural elements, making the helicopter composite amount by weight 50%. They also help reduce production costs by reducing the number of parts needed.

Missiles and Space Vehicles

Many missiles and space vehicles have parts such as rocket motor cases, nozzles, and control surfaces made from composite to help reduce weight and improve performance. Composite properties such as high dimensional stability, low thermal expansion, and excellent thermal and environmental stability make it worthwhile for such uses.

Armor and Protection

Due to their lightweight nature and high compressive strength, composites are highly suitable for producing high-performance armor and protective gear. Not only can they offer protection, but they also increase the productivity and efficiency of those wearing them by allowing them the flexibility to carry other vital tools and equipment.

Satellites

Composite materials have proven to perform well even in the harshest of environments imaginable such as near vacuum at temperatures approaching zero to the highest levels of solar radiation. This makes them ideal for producing those mission-critical components such as satellites to be used in space, where conditions can be extremely unforgiving.

Challenges and Future Developments

The increasing fuel costs have put pressure on aerospace manufacturers to enhance aircraft performance, which can be realized with weight reduction. Based on the developments being made in composite fabrication techniques, it is likely that future aircraft will be made using more composite materials. However, for that to happen, some obstacles must be overcome first. They include

  • High cost of raw materials
  • If a repair is needed, the cost can be very high. Also, it is challenging to identify weaknesses and damage to composites raising safety concerns.
  • Some composites involve a complex and lengthy fabrication process, which costs time and money.
  • There is still a lot to learn and improve with composites meaning engineers and manufacturers must invest time and money to achieve the desired results.

Final Remarks

Aerodine Composites specializes in the design application of high-performance lightweight composite structures that can be used in motorsports, aerospace, and defense industries. We work as a seamless extension of your internal teams to help you achieve your business goal and meet customers’ expectations. We will walk every step of the journey with you, from concept development, design for manufacturability, tooling, prototyping, and manufacturing to the final stage of quality assurance. Contact us today to experience our collaborative approach from the first interaction until the end, when your needs have been met.

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