Composite material: a solid product consisting of two or more independent physical phases, including a matrix material and a reinforcing material. Composite materials are divided into three categories: natural composite materials such as wood, bone, muscle, etc.; mesoscopic composite materials such as alloys, reinforced plastics, etc.; macroscopic composite materials such as reinforced concrete. Composite materials suitable for engineering structures have the following three characteristics:

(1) Contains two or more materials with different physical properties that can be separated by mechanical means;

(2) it is possible to artificially control the distribution of one material over other materials to achieve the best performance;

(3) Performance is better than individual component materials and has unique properties.

Composite materials produced and used in mechanical engineering include two types of materials: reinforcing materials and matrix materials. For example, FRP composite material, the matrix material is resin, which is a dispersion medium, the reinforcing material is glass fiber, which is a dispersed phase, in addition, there is a third phase between the reinforcing material and the matrix. resin, which is their interface. The organic combination of these three components gives the FRP composite material superior properties that individual components cannot possess. This is also one of the main reasons for the rapid development of composite materials.

Reinforcement: Provides strength and rigidity. Form: predominantly fibrous. Material: fiberglass, carbon fiber, kevlar fiber, boron fiber, silicon carbide fiber, etc.

Matrix material: bind the reinforced material together, protect the reinforced material, transfer the load and prevent the crack from expanding.

Material: synthetic resin (divided into thermoset resin and thermoplastic resin), metal, ceramic, cement, etc.

According to the different composite materials of the matrix, it can be divided into:

Polymer matrix composites, also known as fiber-reinforced plastics. Divided into thermoset plastics reinforced with FRP fiber and thermoplastics reinforced with FRTP fiber. The most widely used fiberglass reinforced plastic GRP (Glass Reforced Plastics);

Metal matrix composite materials: such as continuous or discontinuous boron fiber, aluminum, magnesium, titanium, nickel and other carbon fiber reinforced metal matrices;

Composite materials with ceramic matrix: e.g. carbon fiber, ceramic reinforced with silicon carbide (SiC) whiskers, which significantly increases the impact strength of ceramics (up to 9 times higher fracture toughness);

Composite materials on the baseve of cement: such as carbon fiber, glass fiber, vegetable fiber reinforced cement, etc.; carbon matrix reinforced with carbon fiber is called C/C composite material.

The above composite materials, polymer-based composite materials, are currently the most widely used in the world.