ME or MEng Master of Engineering Master of Engineering Machine Design 5 â Questions and Answers
Question 1: The Palmgren-Miner rule is used in machine design to:
- Calculate bearing load ratings
- Predict cumulative fatigue damage under variable amplitude loading (Correct answer)
- Determine gear contact stress
- Estimate stress concentration at notches
Correct answer: Predict cumulative fatigue damage under variable amplitude loading
Miner's rule states failure occurs when ÎĢ(ni/Ni) = 1, summing cycle ratios across all stress levels.
Question 2: Which snap-ring groove feature most critically affects the fatigue life of a shaft?
- Groove width
- Groove depth
- Corner radius at the groove bottom (Correct answer)
- Snap-ring material
Correct answer: Corner radius at the groove bottom
A sharp corner at the groove bottom is a severe stress concentration that dominates fatigue crack initiation on the shaft.
Question 3: A spur gear pair has a velocity ratio of 4:1 and a center distance of 250 mm. If the pinion has 20 teeth, the module is:
- 4 mm
- 5 mm (Correct answer)
- 2.5 mm
- 10 mm
Correct answer: 5 mm
Gear has 80 teeth; total teeth on centers: m(N1+N2)/2 = 250 â mÃ100/2 = 250 â m = 5 mm.
Question 4: In hydrodynamic journal bearing design, the Sommerfeld number S is used to determine:
- Bearing temperature rise only
- Minimum film thickness, friction, and flow characteristics (Correct answer)
- Maximum load capacity only
- Oil viscosity grade selection
Correct answer: Minimum film thickness, friction, and flow characteristics
The Sommerfeld number S = (r/c)Âē(ΞN/P) consolidates design variables and maps to bearing performance parameters via charts.
Question 5: When a machine component is designed using a safety factor of 2.5 based on yield strength, the design stress is:
- 2.5 Ã Sy
- Sy / 2.5 (Correct answer)
- Sy à 2.5 / Su
- Su / 2.5
Correct answer: Sy / 2.5
Design (allowable) stress = Sy / n = Sy / 2.5, ensuring the working stress stays well below yielding.
Question 6: In a leaf spring, adding more leaves (laminations) of the same width and thickness primarily:
- Increases stiffness and load capacity without changing stress (Correct answer)
- Reduces stiffness and stress proportionally
- Increases load capacity with no change in stiffness
- Reduces maximum deflection only
Correct answer: Increases stiffness and load capacity without changing stress
Additional leaves increase the effective second moment of area, raising both stiffness and load capacity while the bending stress formula remains the same.
Question 7: The critical speed of a rotating shaft is most effectively raised by:
- Increasing shaft length
- Reducing shaft diameter
- Shortening the shaft span or increasing shaft diameter (Correct answer)
- Adding more bearings at mid-span only
Correct answer: Shortening the shaft span or increasing shaft diameter
Critical speed â â(EI/m) per unit length; a shorter, stiffer (larger diameter) shaft raises the critical speed.
ME or MEng Master of Engineering Master of Engineering Machine Design 5
The Palmgren-Miner rule is used in machine design to: