BME Materials Science 3

Question 1

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

Accepted Answer

Static fatigue (stress corrosion cracking)

Answer

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

Question 2

The Avrami equation is used to describe:

Accepted Answer

Kinetics of phase transformations

Answer

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

Question 3

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

Accepted Answer

In parallel (isostrain condition)

Answer

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

Question 4

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

Accepted Answer

Vacancy diffusion

Answer

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

Question 5

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

Accepted Answer

Below this stress amplitude, fatigue failure will not occur

Answer

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

BME - Bachelor of Mechanical Engineering Practice Test

BME - Bachelor of Mechanical Engineering Practice Test

BME Materials Science 3