- #1
Understanding Composite Bar Angle of Twist: Material Differences Explained
- Thread starter chetzread
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Discussion Overview
The discussion revolves around the concept of the angle of twist in composite shafts made of different materials. Participants explore why the angle of twist must be the same at junctions of the bars despite the materials differing, and how this relates to the twisting moments applied to each bar.
Discussion Character
- Debate/contested
- Technical explanation
- Homework-related
Main Points Raised
- One participant questions why the angle of twist must be the same for two bars made of different materials, suggesting that they would have different twisting angles under the same moment.
- Another participant asserts that for a composite shaft, it is necessary for the angles of twist at junctions to be equal to prevent the shaft pieces from coming apart.
- There is a discussion about the definition of twisting moments and how they apply to the bars in question, with a participant noting that the torsion applied to both bars may not be the same.
- Some participants emphasize the importance of the angles of twist being equal at the junctions to ensure the integrity of the composite shaft.
- One participant references specific equations from a document to support their points regarding the angles of twist at junctions.
- There is a suggestion that the composite shaft is a single entity rather than two separate shafts, implying that they are connected in some manner.
Areas of Agreement / Disagreement
Participants express differing views on the necessity of equal angles of twist for composite shafts, with some supporting the idea while others question it based on material differences. The discussion remains unresolved with multiple competing viewpoints.
Contextual Notes
Participants have not reached a consensus on the definitions and implications of twisting moments and angles of twist, leading to uncertainty about the conditions under which the angles must be equal.
- #2
BvU
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For a composite shaft, it is useful if the shaft pieces do not come apart at junctions (like point B) 
. That means ##\phi_1 = \phi_2## !
. That means ##\phi_1 = \phi_2## !- #3
chetzread
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Why?BvU said:For a composite shaft, it is useful if the shaft pieces do not come apart at junctions (like point B)
- #4
chetzread
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why the twisting angle are the same? they are different materials, when same twisting moment applied to them , both of them will have different twisting angle,right?BvU said:For a composite shaft, it is useful if the shaft pieces do not come apart at junctions (like point B)
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BvU
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What about T = T1 + T2 + T3 + ... ?
Can you check how 'twisting moment' is defined ?
Can you check how 'twisting moment' is defined ?
- #6
chetzread
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ok,i noticed that the torsion(moment ) applied on both bar are not the same,but why are the twisting angle same?BvU said:
- #7
BvU
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If they are not the same, then the parts of the shaft have rotated wrt one another. That's not good at all.
Are we talking abouthttp://www.colorado.edu/engineering/CAS/courses.d/Structures.d/IAST.Lect07.d/IAST.Lect07.pdf here ?
Work out (7.10) and (7.11) for your composite bar ABC. Surely, at point B you want ##\phi## from bar AB to be the same as ##\phi## from bar BC at point B ?
I think that's what he means: at point B ##\phi## from bar AB is ##\phi_1## and ##\phi## from bar BC is ##\phi_2##.
Are we talking abouthttp://www.colorado.edu/engineering/CAS/courses.d/Structures.d/IAST.Lect07.d/IAST.Lect07.pdf here ?
Work out (7.10) and (7.11) for your composite bar ABC. Surely, at point B you want ##\phi## from bar AB to be the same as ##\phi## from bar BC at point B ?
I think that's what he means: at point B ##\phi## from bar AB is ##\phi_1## and ##\phi## from bar BC is ##\phi_2##.
- #8
chetzread
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so, the torsion here don't allow the parts of the shaft have rotated wrt one another?BvU said:
It's not stated in the question, how do we know that?
- #9
BvU
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They mention a (one) composite shaft - not two separate shafts that happen to be in each other's neigborhood. . So they are welded (or glued or screwed, or ..) together.
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