×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Torsion Shaft Calculations

Torsion Shaft Calculations

Torsion Shaft Calculations

(OP)
We had the output shaft of a torque wrench fail.  The torque wrench is rated for 3200 ftlbs.  The square output shaft is practically 1.08 inches square.  According to the formula I used [ Max Torque = (2/9)x shear stress x(width of square)^3, where shear is .42*yield], the shaft would have to be made of 417ksi material.  Hardness testing a new shaft resulted in HRC between 42-46 on the outside, suggesting a yield of around 217ksi at best.

I'm I looking at this wrong, or is the torque wrench over-rated?  We found the same problem with another top brand as well.

RE: Torsion Shaft Calculations

Max shear stress in a square section (from Roark) is in the center of the flat side,

Max. Τ = 0.601 T / a3

where 2a is the length of the square side.

so, for a 1.08 square, at 3200 in-lb, the max shear stress would be 12 ksi and a bit; well within the allowable shear for even a mild steel tool (but not much margin there).  At 3200 ft-lb, the max. shear is 146 ksi and a bit; this would require 300 ksi material not to yield, and no margin of safety.

Are you sure about the tool's rating?  Most common 1" drive socket tools have a max. torque rating closer to 1000 to 1200 ft-lb., though I've seen one rated a little over 2000 ft-lb.

RE: Torsion Shaft Calculations

Possible strain hardening?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources