The Age of Composite Materials: History, Classification & Applications

A composite material is a blend of two or more materials with different chemical and physical properties. Upon combination, they aim to serve a specialized purpose: increasing strength, reducing weight, improving electrical resistance, and more.

Engineers often come across problems that call for unique solutions. They usually require multiple improved physical properties like weight, strength, etc. simultaneously.

Unfortunately, many naturally occurring contenders often lack in one aspect or the other. This increases the number of materials needed as well as the cost of procuring them. Add to that the added costs of modifying them according to needs and logistics, and now you have budget issues to deal with.

Composite materials have swooped in and shown immense promise in unifying multiple production and manufacturing sectors. Easily available materials like glass fiber, carbon fiber, and polymers are brought together in a mesh known as a matrix. Many other alternatives like nano-particles and graphene are also widely used in a matrix.

In this piece we aim to cover these aspects of composite materials:

• History
• What are composite materials?
• Types by matrix material
• Types by reinforcement structure
• How composite materials are made
• Examples in use

Because of their huge potential, the production of composite materials is one of the fastest-growing businesses out there. Many factors make composites the avant-garde of the manufacturing industry. This piece aims to signify the huge role it plays in our present and potentially even bigger in the future.

Let us dig into it.

History

The concept of composite materials first came into existence when over 6000 years ago some Egyptian engineers came together and mashed straw and mud to form bricks. Around a similar era, Mesopotamians in Iraq glued strips of wood on top of each other at various angles to create plywood. During the 17th century, the traditional bows in Mongolia were replaced by composite bows made of horn, wood, and sinew. It was called the ‘Mongol bow’. The bow was capable of storing more energy than the regular wooden bow of the same length.

Fast forward to the industrial revolution and the rise of polymers and plastic. It led to widespread applications especially due to its high resistance to heat and electricity. The glass fiber resins invented in the 1930s are still a prominent technology in today’s composite market.

But it was the invention of carbon fiber in the 60s that opened up a lot of potential applications of this composite technology.

In the last few decades, scientists and researchers have developed and classified composite materials on multiple bases. Let us take a look.

What Are Composite Materials?

Composite materials, by definition, comprise at least two materials. In a combination, each takes up a distinct phase: the matrix phase or the dispersed phase.

The matrix phase

The primary phase with a continuous character is called the matrix. It holds together the dispersed phase, sharing a load with it. The matrix is often more malleable and ductile.

The dispersed phase

The secondary phase that is embedded in the matrix in a discontinuous form is the dispersed phase. Since it is often stronger than the matrix, it is recognized as the reinforcing phase.

Now the classification of composites is largely based on the materials of the matrix phase and the dispersed phase. In the next section, we will classify composites based on matrix material and reinforced material structure.

Types of Composite Materials by Matrix

1. Metal Matrix Composites (MMC)
2. Ceramic Matrix Composites (CMC)
3. Polymer Matrix Composites (PMC)

Metal Matrix Composites (MMC)

As the name suggests, the matrix of this composite material is made from metal. A lighter metal is preferred for structural applications, like aluminum, magnesium, or titanium. This provides compliant support for the reinforcement and the structure as a whole. The image below of a turbofan is manufactured out of MMC material. It is lightweight, which helps in improving the fuel efficiency of the aircraft.

Ceramic Matrix Composites (CMC)

In this type of composite, ceramic fibers are embedded in a ceramic matrix phase. This type of structure overcomes the low crack resistance problems faced by conventional ceramic structures. Materials like carbon, silicon carbide and alumina are prime candidates for both the matrix and the dispersed phase.

In the image below, the shaft sleeves for big pumps were manufactured using SiC-fiber reinforced SiC material via chemical vapor infiltration.

Polymer Matrix Composites (PMC)

This type of composite consists of polymer matrices that bind together various short or continuous fibers. The matrices are most often thermosets of resin systems like epoxies, phenolics, and polyamides. PMCs are known for their lightweight, high stiffness, and high strength.

Types of Composite Materials by Reinforcement

1. Particle-reinforced composites: dispersion strengthened, particulate
2. Fiber-reinforced composites: continuous fiber, discontinuous fiber
3. Structural composites: laminar, sandwich structure

Particle-reinforced composites

These are one of the most widely used classes of composite structures due to their ease of availability while being economical. They can be further distinguished based on the strengthening mechanism: particulate and dispersion-strengthened.

Dispersion strengthened

The size of the particles is comparatively smaller, ranging from 0.01 to 0.1 µm. The strengthening occurs at the atomic and molecular level, similar to precipitation hardening in metals. Examples: thoria (ThO2) dispersed nickel alloys have high-temperature strength; Sintered Aluminium Powder (SAP), where minute flakes of alumina are dispersed on an aluminum matrix.

Particulate

This class of composite contains relatively large amounts of coarse particles. They are often designed to produce unusual combinations of properties rather than necessarily improve them. They can be used with all three matrix types: MMC, CMC and PMC. Example: tungsten carbide or titanium carbide embedded with cobalt or nickel, used to make power-cutting tools.

Fiber-reinforced composites

Fiber-reinforced composites provide improved mechanical properties such as strength and strength-to-weight ratio. They incorporate strong, stiff but brittle fibers into a softer, ductile matrix. The matrix acts as a medium to transfer the load to the fibers, which do the majority of the heavy lifting. They are further classified as either continuous or discontinuous fibers.

Continuous fiber-reinforced composites

In continuous fiber composites, the length of the fibers can vary from a few feet to several thousand feet long. A large advantage is that by allowing a uniform orientation of the raw composite fiber, important design criteria (strength, Y-modulus, CTE) can be enhanced and customized. As a whole, continuous fiber composites tend to be more expensive than their short, discontinuous counterparts. But they make up for it by providing significantly improved performance.

Discontinuous fiber-reinforced composites

This sub-division breaks down further into discontinuous aligned fibers and discontinuous randomly oriented fibers.

• Discontinuous aligned fiber composites have shorter lengths of highly condensed fibers aligned in one fixed direction in a matrix. They can demonstrate mechanical properties comparable to unidirectional continuous fiber composites, but the shorter fibers result in diminished ductility, making them ideal for high-strength, low-ductility applications.
• Discontinuous randomly-aligned fiber composites are made up of short, condensed fibers embedded in all directions of a matrix. Aligned fiber composites have heightened mechanical properties only in the direction of the reinforcement; this anisotropy can be avoided by randomly embedding the fibers equally in all directions. While this may result in decreased peak strength, it provides increased formability at a reduced cost.

Structural composites

Structural composites are a special class of composites. Their properties depend not just on those of the constituents but also on the geometrical design of various structural elements. Two widely used classes are laminar composites and sandwich composites.

• Laminar composites are composed of two-dimensional sheets or layers that have a preferred strength direction. According to specific needs, these layers are stacked and cemented together. Materials like metal sheets, cotton, paper, and woven glass or carbon fibers are embedded in a plastic matrix.
  Thin coatings, thicker protective coatings, claddings, bimetallics and laminates are some examples.
• Sandwich structures consist of thin layers of a facing material joined to a lightweight filler core. Each individual material has either high strength or directional rigidity, and the composite possesses both. The core separates the faces, resisting deformation while providing shear rigidity along the planes perpendicular to the faces. Typical face materials include aluminium alloys, fiber-reinforced plastics, titanium, steel and plywood, while core materials are often foamed polymers, synthetic rubbers, inorganic cement, aluminum honeycomb and balsa wood.

How Composite Materials Are Made

Fabrication of composite materials often includes wetting and mixing the reinforcement with the matrix. It then goes through a heat or chemical reaction to bind them into a rigid structure. Preset molds are formulated according to characteristics like the type of materials used, the order and ways of introducing material, the required constituents, and more. Our own manufacturing processes draw on several of the methods below.

Conventional methods

• Wet layup
• Filament winding
• Pre-preg layup (manual or automated)
• Resin transfer molding (or modified, like VARTM) (can be used for chopped fiber composites as well)

Modern methods

• Advanced fiber placement
• Fiberglass spray lay-up process
• Z-pinning

Let’s have a look at a few of these.

Wet layup

Possibly the oldest and still most widely used process for composite fabrication, the wet layup is done by laying down the reinforcement material on the mold, then pouring, mixing or applying the resin material on it using a brush, a roller, or even by hand.

Filament winding

This technique is mostly used for manufacturing open-end structures such as cylinders. Filaments are wound under tension over a rotating mandrel. Glass and carbon are the most common filaments, impregnated with resin as they wind onto the mandrel. As with advanced fiber placement, the angle of the fiber wound affects the properties of the final composite, and it is one of the processes in our own composite manufacturing technology.

Pipes, bicycle spokes, power poles, aircraft fuselages, rocket ignitors and lamp posts are among the applications where filament winding is fast finding a home.

Advanced fiber placement

This can be said to be the 3D printing of a continuous fiber composite. One of the more advanced processes, its claim to fame is offering lighter materials with equivalent or greater strength than metals.

It is an automated process where synthetic resin-impregnated fibers are heated on complex tooling molds. A few bundles of carbon fibers impregnated with epoxy resin are fed to a heater and roller on the fiber placement machines. The angle of placement of these bundles is determined according to the type of fiber-reinforced composite required. This is the family of processes our own automated fiber placement technology belongs to.

Fiberglass spray lay-up process

This method, also called the chop process, conjures fiberglass objects by spraying strands of glass out of a pneumatic gun.

It is an open-molding process where resin and reinforcements are sprayed onto a reusable mold. The spray-up is used to compact the laminate, following which a secondary spray-up layer embeds the core between the laminates.

This is one of the most economical processes for production of small to medium volume parts.

Z-pinning

True to its name, this technique inserts reinforcing fibers along the Z-direction of the plastics. Metals are the preferred choice of fibers for this method.

It can dramatically improve the strength and durability of several materials, especially resistance to delamination. It has found a niche in the automotive and aircraft industries because of its ability to perform under high-pressure conditions.

There are many more methods used for composite fabrication. These are mostly variations or a mix of those mentioned above.

Examples of Composite Materials in Use

The digital revolution of the last few decades has substantially altered the perception of technology, and the possibilities seem boundless with every new day.

Advances in the composites market and its manufacturing technologies have seen a surge in range of applications: aerospace, drones, construction, corrosion-resistant equipment, consumer appliances and more.

Drones

In just a few years, drones have found applications from surveillance to food delivery and photography. The payload of a drone has a huge impact on flight time and power usage. To improve the weight reduction of UAVs, composite materials play a crucial role in design and manufacturing. They are capable of substituting conventional materials like aluminum, which is convenient for drone fabrication but causes higher overall weight.

Aerospace

The lightweight and high specific strength is a huge plus if one wants to dominate the aerospace industry. Add characteristics like fatigue and corrosion resistance, a higher degree of optimization, and potential economy, and composite materials fit like a glove.

The image above depicts the overall composition of materials used in a typical Airbus A350. 53% of the materials account for the use of composite materials.

According to the above graphic, the last half a century has seen a massive shift in the methods of production of aircraft parts. The red dotted line depicts the percentage of composites used in an aircraft. Nearly 80% of an aircraft in 2020 uses a composite material of some kind, compared to about 5% in the 1980s. AFP (automated fiber placement), ATL (automated tape laying), wet layup, filament winding (FW), HLU (hand layup) and other fabrication processes are mentioned in the legend.

Construction

The civil and construction business has found a home for composite materials for a long time. Cladding, drywalls, furniture, building cores and foundations have all been aided by the versatility of composite material.

Fiber-reinforced plastic composites possess high tensile strength, fatigue resistance and low mass, all of which are requisite for a civil engineer.

Floors, bearing pads, concrete structures with steel plates or bars in a sandwich structure, beams and bars, and wood panels are a few examples of composite presence in the construction arena.

Sports

There are hardly any aspects of life untouched by composites. An interesting area where they have taken a stronghold is sports and recreation: from racing helmets and protective gear to tennis rackets and hockey sticks. You would be hard-pressed to find a sport where composites have failed to rear their head.

Consumer appliances

Electronic appliances like phones, home appliances, insulator boards, component systems, circuit breakers, lighting devices and insulated wires all contain composite materials in some form or another.

Conclusion

With every passing day, the composite industry is becoming more lucrative. The global composite materials market is projected to grow at roughly 8% a year through 2033, with carbon fiber the fastest-growing product segment at close to 9%, according to Grand View Research.

To sum up, a composite material is a blend of two or more materials with different chemical and physical properties.

With applications ranging from aerospace and automotive to healthcare and electronics, from papier-mâché articles to skyscrapers, composites have taken over the world. The processes that make them are changing just as fast: see our piece on automated composite manufacturing for where that is heading.

If you are looking for an alternative material for your manufacturing project, there is likely a composite that fits your needs, whether that is a marine structure, a robotics component, or something nobody has built before.

Working out whether a composite is right for your part? Talk to our team.

Frequently Asked Questions

What are composite materials?

Composite materials combine two or more materials with different properties (such as a fiber and a resin) to produce one that is stronger, lighter or more durable than either on its own. The materials stay distinct within the finished part rather than dissolving into each other.

What are some examples of composite materials?

Carbon fiber, fiberglass, reinforced concrete and plywood are all composites, as are mud-and-straw bricks, the earliest known example. Each pairs a reinforcement with a matrix that holds it in place and transfers load to it.

What are the main types of composite materials?

Composites are grouped two ways. By matrix: metal (MMC), ceramic (CMC) or polymer (PMC). By reinforcement structure: particle-reinforced, fiber-reinforced (continuous or discontinuous), and structural composites such as laminar and sandwich panels.

What is a fiber-reinforced composite?

A composite that embeds strong, stiff but brittle fibers such as carbon or glass in a softer, ductile matrix. The matrix transfers load to the fibers, which carry most of it, giving a high strength-to-weight ratio.

How are composite materials made?

The reinforcement is wetted and mixed with the matrix, then cured through heat or a chemical reaction into a rigid structure. Common methods include wet layup, filament winding, pre-preg layup and resin transfer molding, alongside newer automated processes such as advanced fiber placement.