What are Fiber Reinforced Composites (FRCs)?

Keywords:

Reinforcement; Matrix; Interface; Types of Composites

Introduction to Composites

All engineering materials we encounter in our daily lives can be broadly divided into three categories: (1) metals, (2) polymers and (3) ceramics. Sometimes, the properties of these materials are unable to meet our requirements, consequently, we make composites by mixing together two or more constituent materials from these categories, as shown in Figure 1, to achieve the desired properties. You should keep in mind that the composites are developed by macroscopic mixing of constituents which distinguish them from metal alloy counter parts in which constituents are soluble in each other.

Figure 1. Structural materials vs composites

Now, let us further dig into the composites constituents. One of the constituents in a composite is called the reinforcement that is embedded to the other constituent, called the matrix, to improve its properties. The reinforcement material is strong and discontinuous e.g. in the form of fiber, particles or flakes, while the matrix materials is weak and continuous. There exist a region between the reinforcement and the matrix called interface as in shown in Figure 2.

Figure 2. Composites: reinforcement, matrix and interface constituents

Types of composites

• Based on matrix materials

According to the nature of matrix material, the FRCs can be divided into metal matrix composites, ceramic matrix composites and polymer matrix composites, as shown in Figure 3. Metal matrix composites are made of metal or alloy matrices (e.g. aluminum, magnesium, titanium, copper etc.) reinforced with boron, carbon or ceramic fibers. Ceramic matrix composites are made of ceramic matrices (e.g. silicon carbide, aluminum oxide, glass-ceramic, silicon nitrides) reinforced with other ceramics fibers. Metal matrix composites and ceramic matrix composites are relatively costly and difficult to manufacture, and have specialized utilization for advance high temperature, high performance structural applications. Polymer matrix composites or simply fiber reinforced plastics composites (FRPCs) are made of polymer matrices (i.e. thermoset and thermoplastic resins) reinforced with glass, carbon, and aramid (Kevlar) or boron fibers. FPRCs are relatively less costly and easier to manufacture. They are light weight as polymer matrix has lower density than metal and ceramic counterparts. Due to their higher specific mechanical properties, they are very popular in aerospace, automotive and high-end sports applications.

Figure 3. Types of composites based on matrix materials

• Based on reinforcement materials
Based on the type, geometry and orientation of reinforcement, the composites can be classified into three broad categories, also shown in Figure 4.

Figure 4. Types of composites based on reinforcement materials

• Particulate composites

These composites consist of particle reinforcements of various size and shapes randomly distributed in the matrix. This random distribution of particles contribute to their almost quasi-isotropic performance.

• Short fibers composites

These composites consist of short fiber reinforcements of relatively longer size in comparison to the diameter, which can be directionally oriented or randomly distributed in the matrix. In the former case, the performance of composite will be highly anisotropic, while, in the latter case, it can be regarded as quasi-isotropic.

• Continuous fiber composites 

These composites are made of long continuous fiber reinforcements, thereby, called fiber reinforced composites (FRCs). If continuous fibers are directionally arranged in the matrix, then, it is called unidirectional fiber composite. If fibers are oriented perpendicular to each other in the matrix, then, it is named cross-ply or woven fabric composites. If fiber are oriented in various directions then it is called multidirectional fiber composites. The mechanical performance of FRCs outclass the particulate and short fiber composites.

About the Author: 

Dr. Khazar Hayat is a professional engineer with almost 15+ year of experience in research, design, analysis and development of products made of fiber reinforced plastics composites (FRPCs). Currently, he is working as an Associate Professor at Mechanical Engineering Department, The University of Lahore, Pakistan, and can be reached by emailing at khazarhayat@gmail.com.