ASME ASME Mechanical Power Transmission 2 — Questions and Answers
Question 1: In ASME/AGMA gear design, 'pitting resistance' (contact fatigue) life is primarily dependent on which stress?
- Bending stress at the tooth root
- Hertz contact stress at the pitch point (Correct answer)
- Shear stress along the pitch line
- Torsional stress in the gear hub
Correct answer: Hertz contact stress at the pitch point
Pitting resistance life depends on Hertzian contact stress at the tooth surface, which causes surface fatigue (pitting) if excessive.
Question 2: What is the advantage of helical gears over spur gears for high-speed power transmission?
- Helical gears eliminate all axial thrust forces
- Helical gears have higher contact ratio, providing smoother and quieter operation (Correct answer)
- Helical gears are always more efficient than spur gears
- Helical gears can mesh at any shaft angle without modification
Correct answer: Helical gears have higher contact ratio, providing smoother and quieter operation
Helical gears have a higher contact ratio because multiple teeth are in contact simultaneously, resulting in smoother, quieter operation at high speeds.
Question 3: In V-belt drive design per ASME/RMA standards, what does 'effective tension' represent?
- The total tension in the tight side of the belt
- The difference between tight-side and slack-side tension, equal to the transmitted force (Correct answer)
- The pre-tension applied during installation
- The tension when the belt begins to slip on the sheave
Correct answer: The difference between tight-side and slack-side tension, equal to the transmitted force
Effective tension is the net force transmitting power, equal to the difference between the tight-side tension and the slack-side tension.
Question 4: What is the primary advantage of a chain drive over a V-belt drive for power transmission?
- Chain drives operate more quietly
- Chain drives have no slip, providing a positive, constant velocity ratio (Correct answer)
- Chain drives require no lubrication
- Chain drives can operate at higher speeds without vibration
Correct answer: Chain drives have no slip, providing a positive, constant velocity ratio
Chain drives provide a positive, non-slip drive with a constant velocity ratio, unlike belt drives which can slip under overload.
Question 5: Under ASME power transmission standards, what is the purpose of a 'service factor' for chain drives?
- To account for speed variation above nameplate RPM
- To modify the rated chain load capacity for the type of driven load and power source (Correct answer)
- To define the chain lubrication interval
- To specify the minimum sprocket diameter for a given chain pitch
Correct answer: To modify the rated chain load capacity for the type of driven load and power source
The service factor for chain drives modifies the chain's rated load capacity to account for the type of load (smooth, moderate shock, or heavy shock) and the type of prime mover.
Question 6: In shaft design per ASME standards, which failure criterion is most commonly used for ductile shaft materials under combined loading?
- Maximum normal stress theory
- Maximum shear stress theory (Tresca)
- Distortion energy theory (von Mises) (Correct answer)
- Fracture mechanics approach
Correct answer: Distortion energy theory (von Mises)
The distortion energy theory (von Mises criterion) is the most commonly used and most accurate failure criterion for ductile materials under combined loading.
ASME ASME Mechanical Power Transmission 2
In ASME/AGMA gear design, 'pitting resistance' (contact fatigue) life is primarily dependent on which stress?