Polymers and Composites Flashcards

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

Answer: Amorphous regions transition from glassy to rubbery behavior

Below Tg, amorphous polymer chains are frozen in a glassy state; above Tg, segments gain sufficient mobility to exhibit rubbery, viscoelastic behavior.

Thermoplastics differ from thermosets in that thermoplastics:

Answer: Can be repeatedly melted and re-formed

Thermoplastics consist of linear or branched polymer chains that soften when heated and solidify when cooled, allowing repeated processing and recycling.

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

Answer: Transfer loads to fibers and protect them

The matrix binds and protects the fibers, transfers applied loads to the fibers via shear, and maintains fiber alignment.

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

Answer: E_c = V_f x E_f + V_m x E_m

The longitudinal (isostrain) rule of mixtures gives composite modulus as the volume-fraction-weighted sum of fiber and matrix moduli: E_c = V_f times E_f + V_m times E_m.

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

Answer: Thermosets

Epoxy resins are thermosets that form a three-dimensional cross-linked network upon curing with a hardener, providing high stiffness, strength, and temperature resistance.

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

Answer: High specific strength and specific stiffness

CFRP provides extremely high strength-to-weight (specific strength) and stiffness-to-weight (specific stiffness) ratios, enabling significant weight savings in structural applications.