Question

What do you meant by compound shaft? How compound shaft be classified?

Answer 1

Shaft made up of two or more materials are called compound shaft. These shaft may be connected in series or in parallel. 

SHAFT IN SERIES: In order to form a composite shaft sometimes two shafts are connected in series. In such cases each shaft transmits the same torque. The angle of twist is the sum of the angle of twist of the two shaft connected in series.

Total angle of twist (θ) = θ₁ + θ₂ = TL₁/C₁I_P1 + TL₂/C₂I_P2 

Where, T = torque transmitted by each shaft 

L₁,L₂ = Respective lengths of the two shafts. 

G₁, G₂ = Respective moduli of rigidity 

I_P1, I_P2 = Respective polar moment of inertia 

→ When shaft are made of same material: than G₁ = G₂ = G  than, 

θ = θ₁ + θ₂ = T/C[L₁/I_P1 + L₂/I_P2] 

SHAFT IN PARALLEL: The shaft are said to be in parallel when the driving torque is applied at the junction of the shafts and the resisting torque is at the other ends of the shafts. Here, the angle of twist is same for each shaft, but the applied torque is divided between the two shaft.

i.e. θ₁ = θ₂ and T = T₁ + T₂ 

if the shaft are made of same material than G₁ = G₂ 

Such a situation (θ₁ = θ₂ and T = T₁ + T₂) also arises when the shaft ends are fixed and are subjected to a torque at the common junction.