Types of Composite Materials

A composite material, commonly shortened to composites, describes material that results from at least two other components, often to form one with superior properties. Yet, despite this bonding, in composites the constituent components are still distinctly identifiable. Traditional materials may serve a limited range of applications, whereas compositional materials are more suitably adapted to address various, often taxing, environments. More advanced than the constituents, composites take on new properties such as strength, stretch, durability, lightness, or resistance to moisture, or electricity, or corrosion.

The resulting composite creates a superior material that is tailored for more advanced applications. Composites can, for example, be engineered to answer the safety critical demands of high-speed motorsport. Another example of superior performance, barrier fabrics and textiles, subjected to hard compliance by the FAA, represents a more advanced application of composites to enhance aerospace activities.

Structure of composites

Composites can be identified based on their structures, or assembly, which can be engineered in different ways to result in unique properties. These commonly include:

  • Those reinforced with particles
  • Those reinforced with chopped strands
  • Laminates
  • Unidirectional composites
  • Fabric reinforcements
  • Honeycomb structures

What are the common types of composite materials?

Though there are many, some more familiar examples of composites include:

Composites woods like plywood

Created from thin layers of overlapping wood, plywood is one of the earliest examples of a composite material. As a common application, these can appear in everyday scenarios from small DIY projects to larger structural ones.

  • Reinforced plastics like fibreglass

A common composite where a polymer matrix is reinforced with fibres. Due to its versatility, its applications can range from industries like aerospace to ballistics.

  • Reinforced concrete

From adding in reinforcements, concrete can be strengthened through steel, polymers and other alternative composites. For more advanced applications, reinforced concrete nowadays feels necessary in building projects, like construction.

  • Ceramic matrix composites

Commonly a subgroup of both ceramics and composites, these consist of ceramic fibres in a ceramic matrix.

  • Metal matrix composites

A composite that is composed of at least two constituents: one is a metal, and the other can be another metal, ceramic, or other compound.

Advanced Applications of Composites

From motorsport to aircraft, aerospace and military application, composites have grown in popularity to answer to the demands of a modern world transitioning into the future. As progressive characteristics are engineered, a composite material becomes uniquely custom to address the pressures and demands of new and exciting industries, which are often those pushing boundaries.

Though it takes an engineer’s trained eye to spot, the applications of a composite are broad and varied, including:

  • Land defence applications: popular ballistic technology has been historically serving the safety of deployed troops and other ground military activities.
  • Energy provision: mission critical to the cultivation of high energy resources, composites provide safety and protection amidst these demanding environments.
  • Automotive: similar to other applications, composites fortify safety protocol, but also enhance performance.

What are the constituents of a composite?

Fibres

Reinforcement fibres can either be classified as a natural fibre (a mineral, for example) or a synthetic one (such as glass). Comparatively, glass fibres are the most popular reinforcement fibre. Its common applications usually target larger, if cost-effective, constructions, such as ships and wind turbines. An example of modern composites – and widely known as the original fibre reinforcement – fibreglass was largely embraced as a textile reinforcement. After continued innovation, fibreglass grew in recognition in the larger global composites market in the US and beyond.

Examples of fibres

The outcome of a fibres properties is shaped not only by the manufacturing process, but the constituent materials and chemistries used.

  • Glass
  • Carbon
  • Aramid
  • Boron
  • Quartz
  • Ceramic
  • Basalt
  • Other natural fibres

The process

When thin strands of silica-based material, lime, alumina and magnesia are heated in a furnace at about 800oC, imparting a viscosity-like consistency into the paste. As the temperature rises, the impurities disappear from the glass, which is then passed along as a transparent mass. Pressured through dies, or platinum plates with small holes, fibres are extruded with small diameters of 5-24μm (the thinner the diameter, the less irritant the product feels against skin). This is produced as glass thread, which is ‘sized’ and dried. This is known to be particularly useful for its insulated and resilient properties, especially to high temperatures.

Other types of glass include:

  • R glass
  • D glass
  • AR glass (alkali resistant)
  • C glass

Glass fibres that are textile-grade are produced from silica (SiO2) sand that’s put under high heat and then cooled. The dynamic between quick cooling rates and risen temperatures, essentially applied heat, results in glass. SiO2 brought to 1720oC, then cooled off, prevents crystallisation which is essential in the formation of glass.

Unlike the lower-costing glass fibres, carbon fibres are engineered to bolster performance-based activities. Progressively more everyday in automotive use, carbon fibres have been used in aerospace applications too. Carbon fibre, also known as graphite fibre, is made form thin crystalline filaments of carbon, twisted and strengthened. It has a greater strength and stiffness than steel, though is lighter weight.

Aramid fibres (aromatic polyamide) is a strong contender for any activity where impact resistance is desired, such as armour and defence. It has a specific type of strength, owed to a low density.

Resins found in composites

Resins, as in composites, are polymers and come in two major groups: thermosets and thermoplastics.

  • Thermoset resins – They feature in the majority of composites, and go through a process called polymerization (sometimes cross-linking), moving from a liquid state into a solid. Thermosetting resins are, then, ‘cured’ through a catalyst or heat. Common examples include polyester, vinyl, and epoxy. They exhibit a useful chemical resistance, amongst other mechanical properties.
  • Thermoplastics – Known for their malleability, thermoplastic resins are recognised for being able to be shaped and reshaped whilst semi-fluid, before returning to a rigid form upon cooling. Common examples range from nylon, PP, and PET – whilst higher performing include PEI or PEEK.

Unsaturated polyester resins (known as UPR) are the most applied in the composites industry. Yet, epoxy resins have a reputation for yielding a variety of performances to match its demand. Resins exist across a variety of systems.

Improving composites with Fillers, Additives & Reinforcements

Fillers materials can improve certain properties, often enhancing a material, whilst reducing its cost (as fewer resins are required). Popularly, fillers are used in everyday applications, or recipes, such as plastics, rubber, paints and even coatings. Balancing additives and filers, material can be engineered with agents that introduce strength and toughness or UV absorption.

What are Intermediate Materials?

Some manufactured commodities require further processing, such as fibres which are engineered into fabrics – whether through knitting, braiding, or needle punched, or woven. Composites, through the likes of textile engineering and other manufacturing, can become more deliberate, if precise, in how they are optimised.

A prepreg is shorthand for a (reinforcing) fabric that has been impregnated with a resin system, such as carbon fibre. Prepregs come ready for curing as tape, cloth, or mat sheets. Typically, prepregs have thermostats that can severely shortened, or limit, the shelf life when exposed to room temperature.

Composites can be expertly engineered and manufactured to address the demands and challenges of many advanced industries. Delivering bespoke material solutions, Permali has a history and reputation for making composites that protect, perform, and are precise. Whatever your application – get in touch to discuss how we can help.