BE/B Eng Bachelor of Engineering Materials Engineering 1 — Questions and Answers
Question 1: What is the crystal structure of most common metals at room temperature called?
- Face-Centered Cubic (FCC), Body-Centered Cubic (BCC), or Hexagonal Close-Packed (HCP) (Correct answer)
- Simple cubic
- Diamond cubic
- Amorphous
Correct answer: Face-Centered Cubic (FCC), Body-Centered Cubic (BCC), or Hexagonal Close-Packed (HCP)
Most engineering metals adopt FCC (e.g., aluminum, copper), BCC (e.g., iron, tungsten), or HCP (e.g., titanium, zinc) crystal structures depending on their atomic bonding.
Question 2: What is the glass transition temperature (Tg) of a polymer?
- The temperature below which a polymer transitions from a rubbery to a glassy, brittle state (Correct answer)
- The temperature at which a polymer melts completely
- The temperature at which a polymer begins to oxidize
- The temperature at which a polymer crosslinks
Correct answer: The temperature below which a polymer transitions from a rubbery to a glassy, brittle state
Below Tg, polymer chain segments lose mobility and the material becomes rigid and brittle (glassy); above Tg, the polymer is rubbery and flexible.
Question 3: What is the purpose of alloying in metals?
- To improve mechanical properties such as strength, hardness, or corrosion resistance (Correct answer)
- To reduce the melting point to near room temperature
- To make metals transparent
- To eliminate electrical conductivity
Correct answer: To improve mechanical properties such as strength, hardness, or corrosion resistance
Alloying adds one or more elements to a base metal to alter its microstructure and enhance properties like strength, ductility, toughness, or corrosion resistance.
Question 4: What does a phase diagram for a binary alloy system show?
- The equilibrium phases present at various temperatures and compositions (Correct answer)
- The mechanical strength as a function of temperature
- The electrical conductivity versus composition
- The diffusion rate of atoms in the alloy
Correct answer: The equilibrium phases present at various temperatures and compositions
A binary phase diagram maps the stable phases (solid, liquid, or mixtures) present in a two-component system across a range of temperatures and compositions.
Question 5: What is the Vickers Hardness Test used to measure?
- A material's resistance to permanent deformation by indentation (Correct answer)
- A material's tensile strength
- A material's resistance to fracture
- A material's thermal conductivity
Correct answer: A material's resistance to permanent deformation by indentation
The Vickers hardness test presses a pyramid-shaped diamond indenter into the material surface under a defined load and measures the size of the resulting indentation to calculate hardness (HV).
Question 6: What is the difference between thermoplastic and thermoset polymers?
- Thermoplastics can be remelted and reshaped; thermosets permanently harden after curing (Correct answer)
- Thermosets are always softer than thermoplastics
- Thermoplastics cannot be recycled under any conditions
- Thermosets have lower melting points than thermoplastics
Correct answer: Thermoplastics can be remelted and reshaped; thermosets permanently harden after curing
Thermoplastics (e.g., polyethylene, nylon) soften when heated and can be remolded repeatedly; thermosets (e.g., epoxy, polyester resin) form irreversible crosslinks when cured and cannot be remelted.
BE/B Eng Bachelor of Engineering Materials Engineering 1
What is the crystal structure of most common metals at room temperature called?