ME Polymers and Composites

Question 1

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

Accepted Answer

Amorphous regions transition from glassy to rubbery behavior

Answer

The polymer melts and flows freely

Answer

Crystalline regions begin to melt

Answer

Chain scission occurs

Question 2

Thermoplastics differ from thermosets in that thermoplastics:

Accepted Answer

Can be repeatedly melted and re-formed

Answer

Are permanently cross-linked after curing

Answer

Cannot be recycled

Answer

Have higher service temperatures

Question 3

In a fiber-reinforced polymer composite, the primary function of the matrix material is to:

Accepted Answer

Transfer loads to fibers and protect them

Answer

Carry the main tensile load

Answer

Provide electrical conductivity

Answer

Increase density

Question 4

The rule of mixtures predicts the longitudinal elastic modulus of a continuous fiber composite as:

Accepted Answer

E_c = V_f x E_f + V_m x E_m

Answer

E_c = V_f x E_f x V_m x E_m

Answer

E_c = E_f / V_f + E_m / V_m

Answer

E_c = (V_f + V_m) / (E_f + E_m)

Question 5

Epoxy resins used as matrix materials in aerospace composites are classified as:

Accepted Answer

Thermosets

Answer

Thermoplastics

Answer

Elastomers

Answer

Semicrystalline polymers

Question 6

Carbon fiber reinforced polymer (CFRP) composites are favored in aerospace because they have:

Accepted Answer

High specific strength and specific stiffness

Answer

High density and high modulus

Answer

Low strength but excellent thermal resistance

Answer

Low cost and high toughness