Full definition
Composite materials are engineered substances created by combining two or more distinct constituent phases, resulting in properties that are superior to those of the individual components. Typically, these materials consist of a reinforcement, such as fibers or particles, which provide enhanced strength, embedded within a matrix, often made of resin or metal, that offers shape and load transfer capabilities. The combination allows for the exploitation of the strengths of each material while mitigating their weaknesses, creating a product that is more effective in specific applications. For example, glass fibers, with a tensile strength of around 3,400 MPa, are economical and widely used, while carbon fibers can achieve tensile strengths ranging from 3,500 to 7,000 MPa, offering the highest stiffness-to-weight ratio. Aramid fibers, such as Kevlar, are renowned for their exceptional impact and cut resistance, making them suitable for applications requiring high durability.
The matrix phase can be categorized into thermosetting resins, which include epoxy, polyester, and vinyl ester, common in industrial fiber-reinforced plastics (FRP), and thermoplastic materials like PEEK and PPS, which provide recyclability and are increasingly used in aerospace applications. Manufacturing methods for composite materials include hand lay-up, filament winding, pultrusion, compression molding, autoclave curing, and resin transfer molding (RTM). Each method has unique advantages that can influence the final properties of the composite.
One of the standout features of composite materials is their anisotropic nature, allowing fibers to be oriented in specific directions to match the anticipated load paths. This can lead to a specific strength that is 3 to 5 times greater than steel while weighing only one-fifth as much, providing design flexibility and corrosion resistance. Common standards that govern the testing of composite materials include ASTM D3039 for tensile strength and ASTM D2344 for shear strength, ensuring consistent quality and performance across applications. Industries utilizing composite materials range from aerospace and automotive to sports equipment and construction, where they are found in components such as wind turbine blades, aircraft structures, FRP tanks, pipes, and gratings.