Shafts

When only power or torque transmission is to be considered, solid shaft will transmit more power but there are other factors also which needs to be considered for shaft design. Shear and bending stresses can be calculated for solid and hollow shafts as below:

Shear (t) and bending (s) stresses on the outer surface of

a shaft, for a torque (T) and bending moment (M)

For solid circular section od =d:

t = T / J* r= T / (π d⁴/32) *d/2 =16T/ π d³

s = M/I * r =M/(π d⁴/64) *d/2 =32M/ π d³

For hollow circular section Od= d_o , ID= d_i :

t = T / J* r= T / {π( d_o⁴ - d_i⁴)/32} *d_o/2 =16Td_o/ π(d_o⁴- d_i⁴)

= 16T/ π d_o³ (1- λ⁴) where λ= d_i / d_o

s = M/I * r = M / {π( d_o⁴ - d_i⁴)/64} *d_o/2 =32Md_o/ π(d_o⁴- d_i⁴)

= 32M/ π d_o³ (1- λ⁴) where λ= d_i / d_o

when comparing a solid and hollow shaft of the same diameter, of course the solid shaft will transmit more torque, but i think you mean't to say what's more durable and practical. when two shafts , "hollow vs. solid", that are designed to transmit the "same" amount of torque, the hollow shaft will be more durable due to it's fexibiaty. solid shafts will eventually fail due to stress fatique from twisting, untwisting,vibration,etc.

i've broken alot of axles racing, but never a drive shaft. i scribe a straight light line along the length of the axles "torsion steel", and drive shaft. the scribe line indicates when the axle or drive shaft has twisted. i twist axles all the time. the scribe line on the drive shaft is still straight.

TOTALLY wrong. If you broke it is because they were not well designed considering all application constrains. From the loading point of view a shaft is a shaft, from the behavior point of view a shaft which is not matched to the loading is a bad design and will fail being full or hollow. Some times full shafts break because of a higher stress local factor again due to bad design.