Composite materials are materials which are a combination of two or more distinct individual materials. These combinations are formed to obtain a more desirable combination of properties. This is called the principle of combined action. One example of this principle is the use of composites for aircraft structures. These composites are designed to be lighter weight with comparable strength to metal structural elements that they are replacing. Typically, a composite is formed with a continuous phase called the matrix. As shown in the figure below, the matrix phase surrounds another phase which is discontinuous and referred to as the dispersed phase.
The purpose of the matrix phase is to keep the dispersive phase in place, transfer stress to the dispersed phase, and protect the dispersed phase from the environment. The purpose of the dispersed phase typically depends on which material type it is composed of:
- Metal dispersive phases are typically used to increase yield strength, tensile strength, and/or provide stability over the life of the product.
- Ceramic dispersive phases are typically used to produce materials which resist fracture.
- Polymer dispersive phases are typically used to increase the modulus of elasticity, yield strength, tensile strength, and/or provide stability over the life of the product.
Composites are typically classified by the type of dispersive phase used: particle reinforced, fiber reinforced, or structural. Further details on these different types of dispersive phase types will be forthcoming in the reading for this lesson, but first please watch this short four-minute video introducing composites. Note that in this video what we are calling the dispersive phase they refer to as the reinforcement phase.
Now that you have watched this video, please proceed to the next section.