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Which correctly describes the main role of the matrix in a fiber-reinforced composite?

  1. AThe matrix carries most of the load, and the role of the fibers is limited to stopping cracks from growing in the matrix and raising toughness
  2. BIt binds the fibers to hold the shape, transfers load to them through interfacial shear, and protects them from the environment
  3. CIts only role is to cancel the thermal expansion of the fibers, and it has no effect on mechanical properties such as strength and stiffness
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Answer: B. It binds the fibers to hold the shape, transfers load to them through interfacial shear, and protects them from the environment

In a fiber-reinforced composite, the strong, stiff fibers carry most of the load, while the matrix holds the fibers in their intended positions and orientations and gives the part its shape. External loads are transferred from the matrix to the fibers through shear at the fiber–matrix interface. The matrix also protects the fibers from damage, moisture and chemicals, and when one fiber breaks it keeps the crack from running straight into neighboring fibers. Saying the matrix carries most of the load reverses the roles of fiber and matrix. The matrix strongly influences the strength perpendicular to the fibers, the compressive strength and the interlaminar strength, so saying it has no effect on mechanical properties is also wrong.

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More Composite materials questions

  1. A composite of carbon fiber and epoxy has a carbon fiber mass fraction of 70%. Taking the density of carbon fiber as 1.80 g/cm³ and that of epoxy as 1.20 g/cm³, and assuming no voids, which value is closest to the fiber volume fraction?
  2. For a composite of aligned continuous fibers, which correctly describes when to use the isostrain and isostress forms of the rule of mixtures?
  3. A composite of glass fibers (Young's modulus 72 GPa) aligned in one direction at a volume fraction of 40% in a resin (Young's modulus 3.0 GPa) is loaded in tension parallel to the fibers. In the elastic range, which value is closest to the fraction of the load carried by the fibers?
  4. A composite contains glass fibers (Young's modulus 72 GPa) aligned in one direction at a volume fraction of 50% in a resin (Young's modulus 3.0 GPa). Using the isostress rule of mixtures, which value is closest to the Young's modulus perpendicular to the fibers?
  5. Which correctly compares carbon-fiber-reinforced plastic (CFRP) and glass-fiber-reinforced plastic (GFRP)?