Which statement best defines a composite material?

• A. Two or more materials combined to create a material with superior properties
• B. Only metals combined
• C. A single-phase crystalline solid
• D. A polymer with a single reinforcement

Answer: (A)

Composite materials are formed when two or more constituent materials with distinct properties are combined to create a new material that has properties not present in any of the constituents alone. This idea is captured by saying that two or more materials are combined to produce a material with superior or tailored properties. It also explains why many useful materials use a matrix and a reinforcement, such as carbon fiber in a polymer matrix or concrete (cementitious matrix with aggregates). The other statements are too limiting: composites are not restricted to metals only, they are not just a single-phase crystalline solid, and while a polymer with a reinforcement is a type of composite, the general definition is broader and encompasses many matrix materials and reinforcements.