What Is a Composite Material?

Advanced composite materials have extensive uses and advantages in the design and manufacturing of products in all industry verticals, including aerospace, automotive, shipbuilding, consumer electronics, medical devices, industrial equipment, and more. Let’s take a look at what composite materials generally are, their history, what they’re made of, how they are made, the different types and their advantages, and use case examples.

A composite material is literally any material that consists of two or more materials. This includes items such as concrete, plywood, and even 6,000-year-old Egyptian mud-straw bricks.

This discussion will focus on advanced composite materials, which are typically strong fiber reinforcement placed in resin. Product development organizations use them because they can be designed for higher strength and stiffness ratios to their weight in comparison to standard materials like steel, aluminum, and titanium. They can also be manufactured to custom shapes for their applications.

Advanced composite materials as we know them are the result of the development of resin materials and fiber reinforcements. Synthetic plastic resins first developed in the modern era include:

• Polystyrene in 1839
• Polyester resins in 1847
• Polyvinyl chloride (vinyl) in 1872
• Phenolic resins in 1907

Chemical companies, scientists, and engineers developed and refined the processes for synthesizing these and other resins for decades. This work continues to this day.

Fiber reinforcement materials developed in the past century led to the use of advanced composite materials in boatbuilding, defense, aerospace, the automotive industry, consumer products, medicine, and other industries. These materials include:

• Fiberglass in 1932
• High modulus commercial carbon fibers in 1964
• Kevlar introduced publicly in 1971
• Nextel 312 ceramic fabric by 3M in 1974

The use of advanced composite materials accelerated during World War II to make aircraft lighter and house radar equipment. Post-war, composites started being used in cars, boats, and even surfboards. Since the 1970s, new materials and methods have expanded the use of composite materials all over the world.

Advanced composite materials typically consist of a fiber reinforcement and a resin (also known as a matrix). Some composite designs also contain a thick but low-density core.

Let’s talk about these in more detail.

Common fiber reinforcements include materials such as glass, Kevlar, carbon fiber, quartz, and boron.

The most common glass fibers include E-glass, known as “electrical glass,” for its insulating properties, and S-glass, high strength and stiffness fibers with high silica content. S-glass can be used in demanding environments like aircraft. Carbon fiber types include PAN (polyacrylonitrile)-based and pitch-based.

Kevlar is commonly known to the public for its use in bulletproof vests and body armor but can also be found as a non-stick ingredient in cookware. Due to its resistance to heat, radiation, and chemicals, Nomex can be found in firefighting gear, flight suits, and uniforms for combat vehicle crewmen.

The fibers can be woven or stitched into unidirectional or multiaxial fabrics, or used as a part of a chopped strand or continuous strand mat.

Resins are polymers, very large molecules that consist of long repeating branches of simpler chemical units known as monomers. Resins can be organic or synthetic. It is placed in a mold with some fibers. During the curing process, it turns from liquid to solid.

The resin matrix holds the fiber reinforcements as well as transfers structural loads from one fiber to the next. Common materials include epoxy, polycyanate, polyester, and vinyl ester.

Additional core material between layers of fiber and resin increases the stiffness and strength in bend and increases resistance to buckling by several times compared to a composite design without a core. However, the weight increases typically by only a few percent.

To keep the additional weight low but add stiffness, the core can consist of a honeycomb structure . These are often hexagonal cells, produced by an expansion method of rolled sheets, a corrugation process, or a molded method. Honeycomb cores are commonly made of Nomex or aluminum. However, there are also foam cores, such as PVC (polyvinyl chloride) and SAN (styrene acrylonitrile).

Fabricating composite products is simultaneously a science, a skill, and an art. Most composites are manufactured using either an open or a closed mold.
To get a general understanding of what’s involved with manufacturing composite products, let’s take a look at a process for Resin Transfer Molding and Vacuum Assisted Resin Transfer Molding.

1. Mix the resins. It is important to mix the resin thoroughly to avoid air bubbles.
2. Prepare the fiber reinforcements from rolls to apply resin. This can involve cutting them, placing them in the mold, and applying narrow strips where parts will meet or intersect.
3. Lay the fiber reinforcements as a dry stack in the mold. Then clamp a second mold over the first.
4. Inject resin into the mold cavity under pressure.
5. If a vacuum is applied to help draw the resin into the mold, the process is known as Vacuum Assisted Resin Transfer Molding.
6. Cure the part in the mold using room temperature, an autoclave, or an oven.
7. Cut and trim to the final shape .

Other molding methods include:

• Injection Molding
• Compression Molding
• Filament Winding
• Pultrusion
• 3D printing
• Manual methods like spray lay-up, wet lay-up, and wet lay-up with vacuum bagging.

Composite parts can also be manufactured from “prepreg,” with is a fabric of fiber reinforcements that come pre-impregnated with a partially cured resin matrix and curing agent. The prepreg can directly be laid into the mold . To complete the curing process, you need heat and pressure.

There are many variations to the processes used to manufacture composite parts. New techniques and processes are being developed every year.

Given the wide variety of materials that can be used as fiber reinforcements and resins, there are numerous classes of composites . Let’s explore a few.

Metal Matrix Composites have a metal like aluminum, magnesium, or titanium as the resin (matrix). The fiber reinforcement can be a metal or a ceramic, such as steel, carbon fiber, silicon carbide, or alumina. The fiber reinforcement can be continuous, discontinuous, or particulates. These composites have high strength-to-weight ratios, strength in both tension and compression, high creep resistance, and lower expansion at high temperatures. They can be found in transmissions, gearboxes, vehicle bodies, and even sports equipment.

Ceramic Matrix Composites, like the name implies, have ceramics as both the fiber reinforcement and resin matrix. Ceramics are solid inorganic non-metallic materials generally characterized by their hardness and resistance to corrosion. The fiber and resin can be either or both carbon, silicon carbide, alumina, or other materials. Given their resistance to both heat and corrosion, they have many applications in engines, turbines, automotives (brakes), and aerospace.

Although fiberglass is a component of GFRPs, the term fiberglass is often used interchangeably as the name of the composite material. One of the first non-military uses of composites was a fiberglass boat hull in 1942. Because of its low cost, it can also be found in storage tanks, piping systems, and various home applications.

These composites are probably the most recognizable to people for their distinct black hatched pattern. The carbon fibers are held in polymer or plastic matrices like the ones listed in the resin section above. Because of the ability to mold them in a wide variety of shapes, they can be found in many industries and applications, including aerospace, automotive, construction, consumer electronics, sporting goods, medical devices and implants, and more.

Composite materials can be found in products of every type because they can be designed to the size, shape, and strength for their use.

Composites can be cured to shapes that are less expensive to machine and result in less waste than the same parts produced in traditional subtractive manufacturing methods (e.g., milling, turning, casting, and injection molding).

Composite parts can be designed to the necessary loads that they will encounter. The incorporation of honeycomb three times the thickness of the fiber-resin thickness can increase stiffness by 30-40 times and strength by over nine times compared to the same structure without honeycomb. This comes at a weight increase of a few percent. This is one reason that composite structures can have higher strength-to-weight ratios than similar parts made of traditional continuous metals like steel, aluminum, copper, brass, bronze, iron, or titanium.

Composite fibers can come in continuous strands, woven rolls, chopped, and particulates. Resins are manufactured into composites in a liquid form that cures to solid form. Therefore, composites can be formed into whatever shapes can be constructed by the mold. Composite materials can also be 3D printed (such as with additive manufacturing).

Depending on the selection of materials for the fiber and resin as well as coatings applied during the manufacturing process, composite materials can be resistant to chemical exposure, corrosion, and moisture penetration.

Depending on the fibers, resin, coatings, and manufacturing processes, composite materials can be engineered to withstand the conditions of their operating environments. This can include resistance to temperature, radiation, and fatigue loading. Composite materials often require less maintenance than similar parts made from metals, plastics, or concrete.

Composites such as CMCs and GFRPs can be made from materials that are electrical insulators, and therefore are incapable of carrying an electrical charge. Other composites are manufactured from materials with low coefficients of thermal conductivity, making them excellent thermal insulators.

Since the 1940s, advanced composite materials have been used in practically every industry. Let’s take a look at a few.

Every aerospace company is concerned with reducing weight. Lower mass directly translates into a vehicle’s performance and capabilities. Rocket companies track the cost per pound or gram. Any weight savings will improve the product. Composites can be found in every area of aircraft, launch vehicles, and satellites, including fuselages, flight surfaces, structural frames, engines, turbines, landing gear, and avionics. The Boeing 787 Dreamliner is the first airliner with an airframe made primarily of composite materials.

There’s a good chance that the highways and bridges you drive your car over are made with composite materials like asphalt concrete, composite pavement, and fiberglass rebar. Although more expensive than concrete, composites are also used in building construction for their weight savings, durability, and corrosion resistance. They are also used in public utilities like power grids and water supplies.

Composite materials can be engineered for heat resistance, electrical conductivity or insulation, and appearance. This makes them ideal for a wide variety of applications, including printed circuit boards, motors, switches, circuit breakers, transformers, housings, shields, antennas, and lighting components.

Are you interested in designing with advanced composite materials? Creo is a best-in-class 3D Computer Aided Design (CAD) solution that will empower your engineers and designers to realize the benefits of composites in your products. You can find more information at PTC’s Composite Part Design and Manufacturing page.