Subtopic: Measurement of force, stress, torque, speed, displacement and acceleration on machine elements – shafts, couplings, keys, bearings and knuckle joints
Question Statement:
In a rigid unprotected flange coupling transmitting power between an engine flywheel and a high-inertia crop chopper, the bolts are fitted into reamed holes. The primary mode of failure considered in the standard design of these coupling bolts under transmitted torque is:
Options:
(A) Direct tension due to centrifugal forces
(B) Transverse shear stress across the bolt shank at the mating flange interface
(C) Bending stress caused by flange deflection
(D) Torsional shear stress within the bolt core
Answer Key:
B
Step-by-Step Solution & Explanation
In a rigid flange coupling with fitted bolts in reamed holes:
- The torque is transmitted through the bolts primarily by transverse shearing across the interface between the two flange faces: $\tau = \frac{2T}{\pi d_b^2 n D_p}$.
- In addition, crushing/bearing stress between the bolt body and the flange hole is evaluated.
- Hence, the primary failure mode is transverse shearing across the shank at the mating interface.