Master of Engineering Machine Design Flashcards
7 cards from real ME or MEng Master of Engineering practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Master of Engineering Machine Design flashcards as text
A ball bearing has a basic dynamic load rating C = 25 kN and carries a radial load of 5 kN. The expected life at 90% reliability in millions of revolutions is:
Answer: 125
L10 = (C/P)³ = (25/5)³ = 5³ = 125 million revolutions for ball bearings (exponent = 3).
In the design of a power screw, self-locking occurs when the lead angle λ satisfies:
Answer: λ < φ (friction angle)
A power screw is self-locking when the lead angle is less than the friction angle (λ < φ = arctan μ).
Which type of gear provides the highest power density and is most efficient for parallel shaft applications?
Answer: Spur gear
Spur gears have the highest efficiency (~99%) for parallel shafts due to pure rolling contact and no axial thrust component.
The endurance limit of a steel part is reduced by surface finish, size, and reliability factors. If Se' = 300 MPa and ka=0.8, kb=0.9, kc=0.897, the corrected endurance limit Se is:
Answer: 194 MPa
Se = ka·kb·kc·Se' = 0.8 × 0.9 × 0.897 × 300 ≈ 194 MPa.
A thin-walled pressure vessel has internal pressure p, radius r, and wall thickness t. The hoop (circumferential) stress is:
Answer: pr/t
Hoop stress σ_θ = pr/t is twice the longitudinal stress pr/(2t) in a thin-walled cylindrical vessel.
In Hertzian contact between two cylinders with parallel axes, the contact stress distribution across the contact width is:
Answer: Elliptical
Hertzian contact between cylinders produces an elliptical (semi-elliptical) pressure distribution across the contact width.
When designing a welded joint under fatigue loading, AWS and AISC specifications reduce allowable stress primarily because:
Answer: Welds introduce stress concentrations and residual stresses
Weld toes and roots act as stress raisers, and tensile residual stresses from cooling significantly reduce fatigue strength.