Materials Science Flashcards

Which ceramic failure mode is associated with slow crack growth under sustained static loading below the fracture toughness?

Answer: Static fatigue (stress corrosion cracking)

Static fatigue in ceramics involves subcritical crack growth driven by chemical attack at crack tips under sustained stress.

The Avrami equation is used to describe:

Answer: Kinetics of phase transformations

The Avrami (JMAK) equation models the fraction of material transformed as a function of time during nucleation and growth processes.

In fiber-reinforced composites, the rule of mixtures predicts longitudinal stiffness when fibers and matrix are loaded:

Answer: In parallel (isostrain condition)

Under isostrain (parallel) loading along the fiber axis, both constituents experience the same strain, giving the upper-bound rule of mixtures for stiffness.

Which diffusion mechanism dominates in metals at temperatures near the melting point?

Answer: Vacancy diffusion

At high homologous temperatures, vacancy concentration is large and vacancy diffusion (substitutional diffusion) dominates bulk transport.

A steel component undergoes cyclic loading. The S-N curve shows an endurance limit at 10^7 cycles. This means:

Answer: Below this stress amplitude, fatigue failure will not occur

The endurance limit is the stress amplitude below which steel can theoretically withstand infinite fatigue cycles without failure.

Which type of polarization in dielectrics has the slowest response to an alternating electric field?

Answer: Space charge polarization

Space charge polarization involves migration of free charges to interfaces and has the lowest frequency response, occurring only at very low frequencies.

The Pilling-Bedworth ratio (PBR) predicts oxidation resistance. A PBR value between 1 and 2 indicates:

Answer: The oxide layer is protective and adherent

A PBR between 1 and 2 means the oxide volume slightly exceeds the metal volume consumed, creating a continuous, protective barrier.