Torque of a Shaft

  • Thread starter 1question
  • Start date
  • #1
67
0

Homework Statement


The question wants me to find the maximum torque.
I do not understand why the solution uses the radius of the smaller part of the shaft rather than the radius of the thicker part of the shaft. Please see the attached image.

Homework Equations



shear stress = (max torque)(maximum radius)/J where J = polar moment of inertia.

J = π/2c^4 where c = max radius of the rod

The Attempt at a Solution



I want to use 37.5mm as the radius (radius of larger part of the shaft), but it is not correct. The formula above directly relates torque T and c (radius), which is why I would assume it would be correct to use the largest c value possible. I would appreciate any insight. Thanks.
 

Attachments

  • shaft.bmp
    228.3 KB · Views: 297

Answers and Replies

  • #2
Simon Bridge
Science Advisor
Homework Helper
17,874
1,655
I do not understand why the solution uses the radius of the smaller part of the shaft rather than the radius of the thicker part of the shaft.
Probably because the diagram shows the torque being applied to the thin part of the shaft.

It's shear stress you are calculating - the bigger part of the shaft may get a torsional (corkscrew) and a centrifugal stress - but to get a shear stress, something has to be pulling on the surface.
I suspect you are just taking your equation too literally - go back to the definition of a shear force and see how that applies to a torque. i.e. what if you applied the torque to the inner surface of a hollow shaft?
 
  • #3
67
0
Probably because the diagram shows the torque being applied to the thin part of the shaft.

Should have seen that, haha. Thank you.
 
  • #4
SteamKing
Staff Emeritus
Science Advisor
Homework Helper
12,798
1,670
The smaller radius shaft must transmit the same torque as the larger radius part.
 

Related Threads on Torque of a Shaft

  • Last Post
Replies
14
Views
1K
Replies
2
Views
1K
  • Last Post
Replies
5
Views
3K
Replies
1
Views
5K
Replies
25
Views
4K
Replies
5
Views
3K
Replies
3
Views
4K
  • Last Post
Replies
4
Views
3K
  • Last Post
Replies
1
Views
7K
Top