Composites

Composites are materials formed from two or more constituent materials with different physical or chemical properties, designed to produce a material with characteristics not available in a single component. Typically a composite consists of a matrix and a reinforcement. The matrix binds the reinforcement, transfers loads, and protects against environmental damage, while the reinforcement provides strength, stiffness, and sometimes toughness.

Common matrix materials include polymers (such as epoxy, polyester, and vinyl ester), metals, and ceramics. Reinforcements include fibers (glass, carbon, aramid), particles, or whiskers. When combined, composites are broadly categorized as polymer matrix composites, metal matrix composites, and ceramic matrix composites. They can also be described by structure: fiber-reinforced, particulate, laminated, or sandwich configurations. Fiber-reinforced composites are the most widely used, with unidirectional, bidirectional, or randomly oriented fibers.

Manufacturing methods vary and include hand lay-up, prepregs, filament winding, pultrusion, resin transfer molding, compression molding, and additive manufacturing. Processing is typically followed by curing or heat treatment to harden the matrix and develop the final properties.

Key properties of composites include high specific strength and stiffness and the ability to tailor performance for specific applications. They often exhibit anisotropy because properties differ with direction. Other considerations include cost, moisture sensitivity, and challenges related to recyclability and end-of-life disposal.

Applications span aerospace, automotive, wind energy, sports equipment, construction panels, and electronic housings. The field has roots in ancient reinforced materials and expanded rapidly in the 20th century, with ongoing research aimed at improving durability, sustainability, and manufacturability.