ME or MEng Master of Engineering Master of Engineering Machine Design 3

Question 1

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:

Accepted Answer

125

Answer

L10 = (C/P)³ = (25/5)³ = 5³ = 125 million revolutions for ball bearings (exponent = 3).

Question 2

In the design of a power screw, self-locking occurs when the lead angle λ satisfies:

Accepted Answer

λ < φ (friction angle)

Answer

A power screw is self-locking when the lead angle is less than the friction angle (λ < φ = arctan μ).

Question 3

Which type of gear provides the highest power density and is most efficient for parallel shaft applications?

Accepted Answer

Spur gear

Answer

Spur gears have the highest efficiency (~99%) for parallel shafts due to pure rolling contact and no axial thrust component.

Question 4

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:

Accepted Answer

194 MPa

Answer

Se = ka·kb·kc·Se' = 0.8 × 0.9 × 0.897 × 300 ≈ 194 MPa.

Question 5

A thin-walled pressure vessel has internal pressure p, radius r, and wall thickness t. The hoop (circumferential) stress is:

Accepted Answer

pr/t

Answer

Hoop stress σ_θ = pr/t is twice the longitudinal stress pr/(2t) in a thin-walled cylindrical vessel.

ME or MEng Master of Engineering Practice Test

ME or MEng Master of Engineering Practice Test

ME or MEng Master of Engineering Master of Engineering Machine Design 3