BME Materials Science 4

Question 1

In the iron-carbon phase diagram, cementite (Fe3C) contains what weight percentage of carbon?

Accepted Answer

6.70 wt%

Answer

Cementite (iron carbide, Fe3C) has a fixed stoichiometric composition of 6.70 wt% carbon.

Question 2

Which type of bonding is responsible for the unique properties of graphite, including its lubricity and electrical conductivity?

Accepted Answer

Covalent bonding within layers and van der Waals forces between layers

Answer

Graphite has sp2 covalent bonding within hexagonal layers and delocalized π electrons that provide conductivity, with weak van der Waals forces between layers enabling easy shear.

Question 3

A material tested in tension shows a distinct upper and lower yield point followed by Lüders band propagation. This behavior is characteristic of:

Accepted Answer

Low-carbon steels with interstitial solute pinning

Answer

In low-carbon steel, interstitial carbon and nitrogen atoms pin dislocations; the upper yield point corresponds to unpinning, after which Lüders bands propagate.

Question 4

The glass transition temperature (Tg) of an amorphous polymer marks the transition from:

Accepted Answer

Glassy (rigid) to rubbery (viscoelastic) behavior

Answer

Below Tg, polymer chain segments are frozen; above Tg, segmental motion becomes possible, giving rubbery, viscoelastic behavior.

Question 5

Which non-destructive testing method uses high-frequency sound waves to detect internal flaws in materials?

Accepted Answer

Ultrasonic testing

Answer

Ultrasonic testing sends high-frequency acoustic waves into a material and detects reflections from internal discontinuities like cracks and voids.

BME - Bachelor of Mechanical Engineering Practice Test

BME - Bachelor of Mechanical Engineering Practice Test

BME Materials Science 4