Composite Materials

The Fiber-Matrix Interface

· In a composite material, the interfacial area between the fibers and the matrix is normally large compared to the external surface area of the material.
· In a cube of composite with linear dimensions of 1 cm, a volume fraction of 60 % fibers with a diameter of 25 mm has an interfacial surface area of 940 cm² compared to an external surface area of 6 cm².
· Interactions between the matrix and the fiber take place across this internal interface and its properties will be important in load transfer, and fiber pullout during fracture.
· Because the thermal expansion of the matrix and the fiber will generally be different, the interface may be in a state of shear even under zero external load conditions if the composite is fabricated at elevated temperatures and used at room temperature.