Which term describes extremely strong single-crystal reinforcement with very small diameter and high length-to-diameter ratio, and is known for being very expensive and difficult to disperse?

• A. Whiskers
• B. Fibers
• C. Wires
• D. Polymers

Answer: (A)

Whiskers are extremely strong, single-crystal reinforcement particles with very small diameters and a high length-to-diameter ratio. That ultra-thin, single-crystal structure gives exceptional strength and stiffness along their length, which is why they’re valued for boosting a composite’s mechanical properties. The tiny diameter allows for a very high aspect ratio, which improves load transfer and the effectiveness of the reinforcement in the matrix. But that combination also makes dispersion in the matrix challenging—whiskers tend to clump or align and are notoriously difficult to distribute uniformly. They are also costly to produce because growing defect-free single crystals at such small scales requires precise, elaborate processes.

Fibers can be strong reinforcements too, but they typically have larger diameters and are not necessarily single-crystal and ultra-expensive. Wires are larger-diameter metallic forms, not the ultra-thin single-crystal reinforcement described here. Polymers are not single-crystal reinforcements and usually don’t exhibit the same high stiffness per cross-section as whiskers.