Final answer:
The matrix phase in a polymer-matrix fiber-reinforced composite functions to separate the fibers and inhibit crack propagation, protect the surface of the fibers, and bind the fibers together to distribute the applied stress.
Step-by-step explanation:
In a polymer-matrix fiber-reinforced composite, the function of the matrix phase is to perform all the options listed: a) separate the fibers and inhibit crack propagation, b) protect the surface of the fibers from being damaged, and c) bind fibers together so that the applied stress is distributed among the fibers.
The matrix phase surrounds and supports the reinforcing fibers, preventing them from coming into direct contact with each other and inhibiting crack propagation. It also acts as a protective layer for the fibers, shielding them from damage. Additionally, the matrix binds the fibers together, allowing the applied stress to be evenly distributed among the fibers.