Change of volume in pure torsion

[joltu]

why change of volume in pure torsion is zero?
if you consider stress in plane with degree of 45 there is normal stress
normal stress can lead to change of volume

 

[Simon Bridge]

define "pure torsion"...

 

[joltu]

Pure torsion appears when exterior forces acting perpendicular to the bar axis
produce only moments of torsion acting along the bar axis

 

[Simon Bridge]

i.e. pure torsion is defined to be the case where the normal stresses are zero.

 

[Chestermiller]

why change of volume in pure torsion is zero?
if you consider stress in plane with degree of 45 there is normal stress
normal stress can lead to change of volume

See what you get if you evaluate the three principal stresses. Do they sum to zero?