Polymers and Composite Materials Flashcards

Particle-reinforced composites differ from fiber-reinforced composites in that particle reinforcements:

Answer: Are approximately equiaxed and do not provide directional reinforcement

Particle reinforcements are equiaxed (similar dimensions in all directions), so they reinforce approximately isotropically rather than providing the high anisotropic reinforcement of fibers.

Cemented carbide (WC-Co) cutting tools are an example of which composite type?

Answer: Cermet (ceramic-metal composite)

WC-Co is a cermet: tungsten carbide (ceramic) particles embedded in a cobalt (metal) binder, combining ceramic hardness with metallic toughness.

In polymer crystallinity, the degree of crystallinity affects which property most directly?

Answer: Density, stiffness, and melting point of the polymer

Higher crystallinity increases polymer density, stiffness (modulus), and melting point because ordered crystalline regions pack more efficiently and resist deformation.

Which manufacturing method is used to produce continuous fiber composites with constant cross-sections, such as rods, tubes, and structural shapes?

Answer: Pultrusion

Pultrusion continuously pulls fiber rovings through a resin bath and a heated die, producing composite profiles with constant cross-sections.

The primary advantage of using Kevlar (aramid) fibers in composites compared to carbon fibers is:

Answer: Better impact and ballistic resistance with lower density

Kevlar fibers excel in tensile strength-to-weight ratio and energy absorption, providing superior impact/ballistic resistance compared to carbon fibers, though they have lower compressive strength.

Sandwich composite structures consist of:

Answer: Thin, stiff face sheets bonded to a lightweight core material

Sandwich composites have thin, high-stiffness face sheets (e.g., CFRP or aluminum) bonded to a low-density core (e.g., honeycomb or foam), providing high bending stiffness at low weight.