Change of volume in pure torsion

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Discussion Overview

The discussion revolves around the concept of volume change in the context of pure torsion, exploring the conditions under which volume change is considered to be zero. Participants examine the relationship between normal stresses and volume change in torsional loading scenarios.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions why the change of volume in pure torsion is zero, suggesting that normal stress at a 45-degree plane could lead to volume change.
  • Another participant seeks clarification on the definition of "pure torsion."
  • A further contribution defines pure torsion as occurring when exterior forces acting perpendicular to the bar axis produce only moments of torsion along the bar axis.
  • It is noted that pure torsion is characterized by the condition where normal stresses are zero.
  • The initial question about volume change is reiterated, with a suggestion to evaluate the three principal stresses to determine if they sum to zero.

Areas of Agreement / Disagreement

Participants express differing views on the implications of normal stresses in pure torsion, indicating that multiple competing perspectives remain regarding the relationship between normal stress and volume change.

Contextual Notes

There are unresolved assumptions regarding the definitions of stress states and the conditions under which volume change is assessed in torsional scenarios.

joltu
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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
 
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define "pure torsion"...
 
Pure torsion appears when exterior forces acting perpendicular to the bar axis
produce only moments of torsion acting along the bar axis
 
i.e. pure torsion is defined to be the case where the normal stresses are zero.
 
joltu said:
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?
 
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