Master of Engineering Machine Design Flashcards

In a clutch or brake design, the uniform pressure assumption is preferred over the uniform wear assumption when:

Answer: The friction surface is new and unworn

Uniform pressure applies to new surfaces before wear occurs; after break-in, uniform wear (p·r = constant) governs.

The Lewis form factor Y in gear bending stress analysis accounts for:

Answer: Tooth geometry and the parabolic beam analogy

The Lewis form factor Y reflects the shape of the gear tooth, derived from treating it as a cantilever beam with a parabolic fillet.

A shaft supported by two bearings carries a concentrated load of 2 kN at mid-span of 600 mm length. The maximum bending moment is:

Answer: 300 N·m

For a simply supported beam with center load: M_max = PL/4 = 2000×0.6/4 = 300 N·m.

Fretting fatigue in machine components is most effectively prevented by:

Answer: Applying compressive residual stress via shot peening

Shot peening introduces compressive residual stresses that close fretting cracks and significantly improve fatigue life.

In a V-belt drive, the angle of wrap on the smaller sheave is reduced compared to a flat belt because:

Answer: The sheave groove increases effective friction, needing less wrap

The wedging action in the V-groove amplifies friction, so V-belts can transmit the same power with smaller wrap angles.

A press-fit assembly between a steel shaft and hub creates an interface pressure p. The maximum hoop stress in the hub occurs at:

Answer: The inner diameter of the hub (interface)

For a thick-walled cylinder under internal pressure, the hoop stress is maximum at the inner radius (interface).

In designing a fatigue-resistant notched component, increasing the notch root radius is beneficial because it:

Answer: Reduces the stress concentration factor Kt

A larger notch root radius reduces stress concentration (Kt approaches 1 as radius → ∞), lowering the local peak stress.