What is the primary role of fibers in a fiber-reinforced composite?

• A. They reduce weight but do not affect strength
• B. They serve only as fillers
• C. They determine color
• D. They provide significant strength improvement due to high tensile strength

Answer: (D)

The key idea is that fibers act as the main load-bearing phase in a fiber-reinforced composite because their tensile strength (and stiffness) is much higher than the surrounding matrix. When the material is pulled, the fibers carry most of the tensile load, while the matrix binds them, distributes stress, and protects the fibers from damage. This combination yields a much stronger, lighter material than the matrix alone, with performance strongly dependent on fiber orientation and the effectiveness of the fiber–matrix interface. So the primary role of the fibers is to provide a significant strength improvement due to their high tensile strength, not to act as fillers or determine color.