Fundamentals of Engineering Materials Science 1 — Questions and Answers
Question 1: What crystal structure does α-iron (ferrite) have at room temperature?
- Face-centered cubic (FCC)
- Body-centered cubic (BCC) (Correct answer)
- Hexagonal close-packed (HCP)
- Simple cubic
Correct answer: Body-centered cubic (BCC)
α-iron (ferrite) has a BCC crystal structure at room temperature, transitioning to FCC austenite above 912°C.
Question 2: Young's modulus (modulus of elasticity) is defined as:
- The stress at which permanent deformation begins
- The ratio of stress to strain in the elastic region (Correct answer)
- The energy absorbed before fracture
- The material's resistance to surface scratching
Correct answer: The ratio of stress to strain in the elastic region
Young's modulus E = σ/ε is the slope of the linear portion of the stress-strain curve where deformation is fully recoverable.
Question 3: A vacancy (point defect) in a crystal lattice is best described as:
- An extra atom squeezed between lattice sites
- An atom displaced to an interstitial site leaving its original site empty
- An atom missing from its normal lattice position (Correct answer)
- A foreign atom substituting for a host atom
Correct answer: An atom missing from its normal lattice position
A vacancy (Schottky defect) is simply a missing atom at a normally occupied lattice site.
Question 4: What is the coordination number (number of nearest neighbors) for an atom in a face-centered cubic (FCC) structure?
- 6
- 8
- 12 (Correct answer)
- 4
Correct answer: 12
In an FCC structure each atom touches 12 nearest neighbors: 4 in its own layer, 4 in the layer above, and 4 in the layer below.
Question 5: The Burgers vector of a dislocation represents:
- The direction of crack propagation in brittle fracture
- The magnitude and direction of the lattice distortion caused by the dislocation (Correct answer)
- The critical resolved shear stress for slip
- The angle of misorientation across a grain boundary
Correct answer: The magnitude and direction of the lattice distortion caused by the dislocation
The Burgers vector characterizes a dislocation by quantifying the magnitude and direction of the lattice slip associated with it.
Question 6: Which of the following is a thermosetting polymer?
- Polyethylene
- Polypropylene
- Epoxy resin (Correct answer)
- Nylon 6,6
Correct answer: Epoxy resin
Epoxy resin forms permanent covalent cross-links upon curing and cannot be remelted or reshaped, making it a thermosetting polymer.
Question 7: Which atomic bonding type is primarily responsible for the high electrical conductivity of metals?
- Ionic bonding
- Covalent bonding
- Metallic bonding (Correct answer)
- Van der Waals bonding
Correct answer: Metallic bonding
Metallic bonding involves a 'sea' of delocalized electrons that are free to move, enabling high electrical and thermal conductivity.
Fundamentals of Engineering Materials Science 1
What crystal structure does α-iron (ferrite) have at room temperature?