ME or MEng Master of Engineering Master of Engineering Machine Design 5

Question 1

The Palmgren-Miner rule is used in machine design to:

Accepted Answer

Predict cumulative fatigue damage under variable amplitude loading

Answer

Miner's rule states failure occurs when Σ(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?

Accepted Answer

Corner radius at the groove bottom

Answer

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:

Accepted Answer

5 mm

Answer

Gear has 80 teeth; total teeth on centers: m(N1+N2)/2 = 250 → m×100/2 = 250 → m = 5 mm.

Question 4

In hydrodynamic journal bearing design, the Sommerfeld number S is used to determine:

Accepted Answer

Minimum film thickness, friction, and flow characteristics

Answer

The Sommerfeld number S = (r/c)²(μN/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:

Accepted Answer

Sy / 2.5

Answer

Design (allowable) stress = Sy / n = Sy / 2.5, ensuring the working stress stays well below yielding.

ME or MEng Master of Engineering Practice Test