ME or MEng Master of Engineering Master of Engineering Machine Design 2 — Questions and Answers
Question 1: A shaft experiences a bending moment of 500 N·m and a torque of 300 N·m. Using the von Mises criterion, what is the equivalent bending moment?
- 583 N·m (Correct answer)
- 800 N·m
- 559 N·m
- 400 N·m
Correct answer: 583 N·m
The equivalent moment by von Mises is √(M² + 0.75T²) = √(500² + 0.75×300²) ≈ 583 N·m.
Question 2: In a bolted joint subjected to an external tensile load, the joint stiffness constant C is defined as:
- kb/(kb + km) (Correct answer)
- km/(kb + km)
- kb × km
- kb - km
Correct answer: kb/(kb + km)
C = kb/(kb + km) represents the fraction of external load carried by the bolt, where kb is bolt stiffness and km is member stiffness.
Question 3: Which failure theory is most appropriate for designing ductile machine components under static loading?
- Maximum Normal Stress Theory
- Von Mises (Distortion Energy) Theory (Correct answer)
- Maximum Strain Theory
- Fracture Mechanics Theory
Correct answer: Von Mises (Distortion Energy) Theory
The Distortion Energy Theory (von Mises) best predicts yielding in ductile materials and is the most accurate for static loading.
Question 4: A helical compression spring has a spring index C = 8. What is the Wahl correction factor (approximately)?
- 1.18 (Correct answer)
- 1.50
- 1.08
- 1.35
Correct answer: 1.18
The Wahl factor Kw = (4C−1)/(4C−4) + 0.615/C = (31)/(28) + 0.077 ≈ 1.18 for C = 8.
Question 5: In gear design, the AGMA service factor Ks accounts for:
- Tooth profile error
- Size effects on material strength (Correct answer)
- Pitch line velocity
- Gear ratio
Correct answer: Size effects on material strength
The AGMA size factor Ks reflects the reduction in material strength with increasing tooth and gear size.
Question 6: A key connecting a shaft to a hub fails in shear. If the key has width w, length L, and the shaft radius is r, the shear stress is:
- T/(r·w·L) (Correct answer)
- 2T/(r·w·L)
- T/(2r·w·L)
- T/(r·w)
Correct answer: T/(r·w·L)
Shear stress τ = F/(w·L) = T/(r·w·L), where F = T/r is the tangential force on the key.
Question 7: The Soderberg fatigue criterion is more conservative than the Goodman criterion because it:
- Uses yield strength instead of ultimate strength as the mean stress limit (Correct answer)
- Ignores stress concentration factors
- Uses a higher safety factor
- Applies only to compressive mean stresses
Correct answer: Uses yield strength instead of ultimate strength as the mean stress limit
Soderberg uses Sy (yield strength) as the mean stress boundary, making it more conservative than Goodman which uses Su (ultimate strength).
ME or MEng Master of Engineering Master of Engineering Machine Design 2
A shaft experiences a bending moment of 500 N·m and a torque of 300 N·m.
Using the von Mises criterion, what is the equivalent bending moment?