The word “composite” means “consisting of two or more distinct parts”. Thus a material having two or more distinct constituent materials or phases may be considered to be a composite material. Reinforcement and the matrix are the two phases of the composite material.
However, we recognize materials as composites only when the constituent phases will not dissolve into one another and have significantly different physical properties, and thus the composite properties are noticeably different from the constituent properties.
A material is considered as the composite material when
- Combination of materials should result in significant property changes
- Content of the constituents is generally more than 10 %
- In general, the property of one constituent is much greater ( ≥ 5) than the other constituent
One constituent is called the reinforcing phase and the one in which it is embedded is called the matrix. The reinforcing phase material may be in the form of fibers, particles, or flakes. The matrix phase materials are generally continuous.
Reinforcement in the Composites
Reinforcement can be fibers, fabric particles, or whiskers. these reinforcements fundamentally used to increase the mechanical properties of a composite.
The main purpose of the reinforcement is to
- Provide superior levels of strength and stiffness to the composite.
- Reinforcing materials (graphite, glass, SiC, alumina) may also provide thermal and electrical conductivity, controlled thermal expansion, and wear resistance in addition to structural properties.
- The most widely used reinforcement form in high-performance composites is fiber tows (untwisted bundle of continuous filaments).
- Fiber monofilaments are used in PMCs, MMCs, and CMCs; they consist of a single fiber with a diameter generally ≥100 μm.
- In MMCs, particulates and chopped fibers are the most commonly used reinforcement morphology, and these are also applied in PMCs.
- Whiskers and platelets are used to a lesser degree in PMCs and MMCs.
Matrix material in the Composites
The matrix material is the homogeneous and monolithic material in which a reinforcement system of a composite is embedded and is completely continuous.
The main purpose of the Matrix is to
- To bind the reinforcements together by virtue of its cohesive and adhesive characteristics.
- To transfer the load to and between reinforcements, the matrix allows the strength of the reinforcements to be used to their full potential by providing effective load transfer from external forces to the reinforcement.
- The matrix provides a vital inelastic response so that stress concentrations are reduced dramatically, and internal stresses are redistributed from broken reinforcements.
- To protect the reinforcements from environments and handling.
- The matrix also provides a solid form to the composite, which aids handling during manufacture and is typically required in a finished part.
- As a continuous phase, the matrix, therefore, controls the transverse properties, interlaminar strength, and elevated-temperature strength of the composite.
- Because the reinforcements are typically stronger and stiffer, the matrix is often the “weak link” in the composite, from a structural perspective.
We have discussed what is the main purpose of the reinforcement and the matrix in the composite materials. If you still have any thoughts in this topic, let us know in the comment section below.