Polymers and Composite Materials Flashcards

The glass transition temperature (Tg) of a polymer is the temperature at which:

Answer: The amorphous regions transition from a glassy, rigid state to a rubbery state

Below Tg, amorphous polymer chains are frozen in place (glassy); above Tg, they gain sufficient mobility to produce rubbery, viscoelastic behavior.

In fiber-reinforced polymer composites, the primary function of the matrix is to:

Answer: Transfer load to fibers and protect them from the environment

The matrix in a composite holds the fibers in position, transfers applied loads to the fibers, and protects them from environmental damage.

Which type of polymer has a three-dimensional crosslinked network that makes it infusible and insoluble once cured?

Answer: Thermoset

Thermosets form irreversible covalent crosslinks during curing, creating a rigid 3-D network that cannot be re-melted or reshaped.

The rule of mixtures for a unidirectional fiber composite loaded parallel to the fibers gives the composite modulus as:

Answer: E_c = E_f × V_f + E_m × V_m

For loading parallel to fibers (isostrain condition), the composite modulus is the volume-fraction-weighted sum: E_c = E_f·V_f + E_m·V_m.

Vulcanization of rubber introduces which type of bonds to improve strength and reduce creep?

Answer: Covalent sulfur crosslinks between polymer chains

Vulcanization uses sulfur to form covalent crosslinks between rubber polymer chains, greatly improving strength, elasticity, and resistance to creep and permanent set.

Carbon fiber reinforced polymer (CFRP) composites are preferred in aerospace applications primarily because they offer:

Answer: High specific stiffness and specific strength (high stiffness/strength per unit weight)

CFRP composites offer exceptional specific strength and specific stiffness (properties per unit density), enabling significant weight savings in aerospace structures.