ME or MEng Master of Engineering Master of Engineering Machine Design 4 — Questions and Answers
Question 1: In a clutch or brake design, the uniform pressure assumption is preferred over the uniform wear assumption when:
- The friction surface is new and unworn (Correct answer)
- The friction surface is fully run-in
- The contact pressure is very low
- The rotational speed is high
Correct answer: The friction surface is new and unworn
Uniform pressure applies to new surfaces before wear occurs; after break-in, uniform wear (p·r = constant) governs.
Question 2: The Lewis form factor Y in gear bending stress analysis accounts for:
- Tooth geometry and the parabolic beam analogy (Correct answer)
- Pitch circle velocity
- Material hardness
- Gear ratio effects
Correct answer: Tooth geometry and the parabolic beam analogy
The Lewis form factor Y reflects the shape of the gear tooth, derived from treating it as a cantilever beam with a parabolic fillet.
Question 3: A shaft supported by two bearings carries a concentrated load of 2 kN at mid-span of 600 mm length. The maximum bending moment is:
- 600 N·m
- 300 N·m (Correct answer)
- 1200 N·m
- 150 N·m
Correct answer: 300 N·m
For a simply supported beam with center load: M_max = PL/4 = 2000×0.6/4 = 300 N·m.
Question 4: Fretting fatigue in machine components is most effectively prevented by:
- Increasing surface roughness at contact interfaces
- Applying compressive residual stress via shot peening (Correct answer)
- Using softer mating materials
- Increasing contact area
Correct answer: Applying compressive residual stress via shot peening
Shot peening introduces compressive residual stresses that close fretting cracks and significantly improve fatigue life.
Question 5: In a V-belt drive, the angle of wrap on the smaller sheave is reduced compared to a flat belt because:
- V-belt drives require larger center distances
- The sheave groove increases effective friction, needing less wrap (Correct answer)
- V-belts are stiffer and cannot conform to small radii
- The speed ratio is always greater than 1
Correct answer: The sheave groove increases effective friction, needing less wrap
The wedging action in the V-groove amplifies friction, so V-belts can transmit the same power with smaller wrap angles.
Question 6: A press-fit assembly between a steel shaft and hub creates an interface pressure p. The maximum hoop stress in the hub occurs at:
- The outer diameter of the hub
- The inner diameter of the hub (interface) (Correct answer)
- Mid-thickness of the hub wall
- The neutral axis
Correct answer: The inner diameter of the hub (interface)
For a thick-walled cylinder under internal pressure, the hoop stress is maximum at the inner radius (interface).
Question 7: In designing a fatigue-resistant notched component, increasing the notch root radius is beneficial because it:
- Increases the stress concentration factor Kt
- Reduces the stress concentration factor Kt (Correct answer)
- Increases the material's endurance limit
- Reduces the mean stress
Correct answer: Reduces the stress concentration factor Kt
A larger notch root radius reduces stress concentration (Kt approaches 1 as radius → ∞), lowering the local peak stress.
ME or MEng Master of Engineering Master of Engineering Machine Design 4
In a clutch or brake design, the uniform pressure assumption is preferred over the uniform wear assumption when: