ME Polymers and Composites 2

Question 1

Which type of polymerization involves the repeated addition of monomers to an active chain end without byproduct formation?

Accepted Answer

Addition (chain-growth) polymerization

Answer

Addition polymerization occurs when monomers with double bonds (e.g., ethylene) add sequentially to a growing chain end initiated by a free radical, cation, or anion.

Question 2

The degree of crystallinity in a semicrystalline polymer affects which property most directly?

Accepted Answer

Density, stiffness, and optical clarity

Answer

Higher crystallinity increases density, stiffness (modulus), and opacity, while reducing impact toughness and transparency in semicrystalline polymers.

Question 3

In particulate composite materials, randomly distributed particles provide:

Accepted Answer

Isotropic property improvements

Answer

Random particle distribution makes particulate composites isotropic, meaning properties are the same in all directions, unlike fiber composites which are anisotropic.

Question 4

The critical fiber length in a short-fiber composite is important because fibers shorter than this length:

Accepted Answer

Cannot be loaded to their full tensile strength

Answer

Below the critical fiber length, shear stress transfer from matrix to fiber is insufficient to load the fiber to its full tensile strength, reducing reinforcement efficiency.

Question 5

Kevlar (aramid) fibers are particularly valued for which combination of properties?

Accepted Answer

High tensile strength, low density, and energy absorption

Answer

Aramid fibers like Kevlar have excellent tensile strength, low density, and high toughness, making them ideal for ballistic protection and lightweight structural applications.

ME - Materials Engineer Practice Test

ME - Materials Engineer Practice Test

ME Polymers and Composites 2