ME Polymers and Composite Materials

Question 1

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

Accepted Answer

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

Answer

The polymer melts and becomes a liquid

Answer

Crystallization of the polymer begins

Answer

Crosslinks between polymer chains begin to break

Question 2

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

Accepted Answer

Transfer load to fibers and protect them from the environment

Answer

Carry the majority of applied tensile loads

Answer

Increase the stiffness of the fibers

Answer

Reduce the density of the composite

Question 3

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

Accepted Answer

Thermoset

Answer

Thermoplastic

Answer

Elastomer

Answer

Semi-crystalline polymer

Question 4

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

Accepted Answer

E_c = E_f × V_f + E_m × V_m

Answer

E_c = E_f / V_f + E_m / V_m

Answer

E_c = (E_f × E_m) / (V_f × V_m)

Answer

E_c = V_f / E_f + V_m / E_m

Question 5

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

Accepted Answer

Covalent sulfur crosslinks between polymer chains

Answer

Hydrogen bonds between polymer chains

Answer

Van der Waals forces between polymer segments

Answer

Ionic bonds within individual polymer chains

Question 6

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

Accepted Answer

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

Answer

Low cost and easy repairability

Answer

Superior electrical insulation

Answer

Better fire resistance than aluminum