Question

The bolts in a rigid flange coupling, connecting two shafts transmitting power, are subjected to:

• A. Axial force only
• B. Torsion only
• C. Bending moment only
• D. Shear force and bending moment

Hint:

In most power transmission components that use pins or bolts (like couplings or keys), Shear is always the primary concern. In couplings specifically, because they are rigid, any vibration or tilt adds Bending to that shear.

Answer 1

The Correct Option is D

A rigid flange coupling uses bolts arranged in a circle to lock two flanges together, allowing torque to be transmitted from the driving shaft to the driven shaft. The forces acting on these bolts are complex during operation. 1. Primary Shear Force: The main purpose of the coupling is to transmit torque ($T$). This torque creates a tangential force ($F_t$) on each bolt: $$F_t = \frac{T}{R \times n}$$ Where $R$ is the pitch circle radius of the bolts and $n$ is the number of bolts. This tangential force acts perpendicular to the axis of the bolt, subjecting it to

Shear Stress.

2. Bending Moment Interaction: In practical applications, shafts are rarely perfectly aligned. Any slight misalignment (angular or parallel) or the weight of the shafts themselves introduces a

Bending Moment into the coupling.

• The bolts must resist these moments as they try to pry the flanges apart.

• This results in bending stresses being induced in the shank of the bolt.

3. Combined Loading: Additionally, when bolts are tightened during assembly, they are put under an initial tension (axial force). However, when considering the power transmission forces mentioned in the question, the dominant forces that the bolts must survive are the combined effects of the

Shear Force from torque and the

Bending Moment from misalignments or shaft weight.