BME Machine Design 1 — Questions and Answers
Question 1: What is the primary purpose of a factor of safety in machine design?
- To increase cost
- To account for uncertainties in load, material, and geometry (Correct answer)
- To reduce weight
- To improve aesthetics
Correct answer: To account for uncertainties in load, material, and geometry
The factor of safety accounts for uncertainties in applied loads, material properties, and geometric tolerances to prevent failure.
Question 2: Which type of stress is induced in a shaft subjected to twisting?
- Bending stress
- Compressive stress
- Shear stress (Correct answer)
- Tensile stress
Correct answer: Shear stress
Twisting a shaft induces shear stress, distributed across the cross-section with maximum value at the outer surface.
Question 3: The endurance limit of a material is the stress below which:
- Plastic deformation begins
- Fracture occurs immediately
- The material can withstand infinite fatigue cycles (Correct answer)
- Creep starts
Correct answer: The material can withstand infinite fatigue cycles
The endurance limit is the maximum cyclic stress amplitude at which a material can theoretically endure an infinite number of load cycles without fatigue failure.
Question 4: In a bolted joint under tensile load, which failure mode is checked first?
- Bearing failure
- Shear failure of the nut
- Tensile failure of the bolt shank (Correct answer)
- Bending failure
Correct answer: Tensile failure of the bolt shank
Tensile failure of the bolt shank is the most critical and commonly checked failure mode in bolted joints under direct tensile loading.
Question 5: What does the 'pitch' of a thread refer to?
- Thread angle
- Depth of thread
- Axial distance between adjacent thread crests (Correct answer)
- Thread diameter
Correct answer: Axial distance between adjacent thread crests
Pitch is defined as the axial distance measured from one thread crest to the next adjacent crest on the same helix.
Question 6: A key connecting a gear to a shaft primarily transmits:
- Axial force
- Torque (Correct answer)
- Bending moment
- Shear force along the axis
Correct answer: Torque
A key is a machine element that fits into keyways on both the shaft and hub to transmit torque between them.
BME Machine Design 1
What is the primary purpose of a factor of safety in machine design?