BME Materials Science 5

Question 1

Which corrosion type occurs when two dissimilar metals are in electrical contact in an electrolyte, causing the more active metal to corrode preferentially?

Accepted Answer

Galvanic corrosion

Answer

Galvanic corrosion occurs because the less noble (more active) metal becomes the anode and dissolves preferentially when coupled with a more noble metal in an electrolyte.

Question 2

Superelastic behavior in shape memory alloys (e.g., Nitinol) is driven by:

Accepted Answer

Stress-induced martensitic phase transformation that is fully reversible

Answer

In superelastic alloys, applied stress induces a martensitic transformation; upon unloading, the martensite reverts to austenite, recovering all strain.

Question 3

In Fick's second law of diffusion (∂C/∂t = D ∂²C/∂x²), what assumption is made about the diffusion coefficient D?

Accepted Answer

D is independent of concentration

Answer

Fick's second law in its standard form assumes D is constant (independent of concentration), simplifying the partial differential equation.

Question 4

Which microstructural feature of cast iron gives gray iron its characteristic fracture appearance and machinability?

Accepted Answer

Flake graphite in a pearlitic matrix

Answer

Gray iron contains graphite flakes that act as stress concentrators, causing fracture along the flakes and producing the characteristic gray fracture surface.

Question 5

The Weibull modulus (m) is used in ceramics to characterize:

Accepted Answer

The variability (scatter) in fracture strength

Answer

A high Weibull modulus indicates low scatter in fracture strength (reliable material), while a low modulus indicates high variability due to flaw distribution.

BME - Bachelor of Mechanical Engineering Practice Test

BME - Bachelor of Mechanical Engineering Practice Test

BME Materials Science 5