Subtopic: Measurement of force, stress, torque, speed, displacement and acceleration on machine elements – shafts, couplings, keys, bearings and knuckle joints
Question Statement:
Which of the following statements regarding square and rectangular sunk keys used in farm machinery shafts are CORRECT?
Options:
(A) A sunk key fits into keyways cut into both the shaft and the hub of the mating element.
(B) The primary failure modes of a sunk key are shear along the interface and crushing against the sides.
(C) A Woodruff key is an adjustable key capable of tilting in a semi-circular key seat.
(D) A taper key is used only when relative axial sliding motion between hub and shaft is required during operation.
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
Statements A, B, and C are correct:
- Sunk keys are half in the shaft and half in the hub.
- Key failure is assessed by shearing stress ($\tau = F / (w L)$) and crushing/bearing stress ($\sigma_c = F / ((t/2) L)$).
- Woodruff keys are semi-circular and can adjust their angle in the keyway.
- Statement D is incorrect: taper keys prevent axial sliding; feather keys or splines are used when axial sliding is permitted.