NCEES Materials Science 3 — Questions and Answers
Question 1: The Charpy impact test is used to measure a material's:
- Hardness
- Fatigue resistance
- Notch toughness (Correct answer)
- Creep rate
Correct answer: Notch toughness
The Charpy test measures impact energy absorbed by a notched specimen, characterizing the material's notch toughness and susceptibility to brittle fracture.
Question 2: Austenite in steel is the FCC phase stable above approximately:
- 727°C (Correct answer)
- 912°C
- 1148°C
- 1538°C
Correct answer: 727°C
For plain-carbon steels, austenite (FCC iron) becomes stable above the eutectoid temperature of approximately 727°C (A1 line on the Fe-C diagram).
Question 3: Which process involves heating steel above the critical temperature and then cooling it in still air?
- Annealing
- Quenching
- Normalizing (Correct answer)
- Tempering
Correct answer: Normalizing
Normalizing consists of austenitizing steel and allowing it to air-cool, producing a finer, more uniform pearlitic microstructure than full annealing.
Question 4: Galvanic corrosion occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte. Which metal corrodes preferentially?
- The more noble (cathodic) metal
- The metal with higher electrical conductivity
- The more active (anodic) metal (Correct answer)
- The metal with higher thermal conductivity
Correct answer: The more active (anodic) metal
In a galvanic couple, the more active (less noble) metal acts as the anode and undergoes preferential oxidation and corrosion.
Question 5: The glass transition temperature (Tg) of a polymer is the temperature at which:
- The polymer melts into a viscous liquid
- The amorphous regions transition from glassy to rubbery behavior (Correct answer)
- Crystallization begins
- Thermal degradation starts
Correct answer: The amorphous regions transition from glassy to rubbery behavior
At Tg, the amorphous phase of a polymer transitions from a rigid, glassy state to a soft, rubbery state as chain mobility increases.
Question 6: Which failure mode is characterized by crack growth under cyclic loading at stresses well below the yield strength?
- Creep failure
- Fatigue failure (Correct answer)
- Ductile fracture
- Stress corrosion cracking
Correct answer: Fatigue failure
Fatigue failure occurs due to progressive crack initiation and growth under repeated cyclic loading, often at stresses far below the static yield strength.
Question 7: Fick's second law of diffusion describes how:
- Diffusion flux relates to concentration gradient at steady state
- Concentration profile changes with time during non-steady-state diffusion (Correct answer)
- Temperature affects the diffusion coefficient
- Grain boundaries enhance atomic diffusion
Correct answer: Concentration profile changes with time during non-steady-state diffusion
Fick's second law (∂C/∂t = D ∂²C/∂x²) governs the time-dependent change in concentration distribution during transient (non-steady-state) diffusion.
NCEES Materials Science 3
The Charpy impact test is used to measure a material's: