Contact US

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!

*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

Maximum torque of aluminium thread

Maximum torque of aluminium thread

Maximum torque of aluminium thread

I am new on the forum. Unfortunately, I have never had a "Strength of Materials" lessons, that sorry if my question is silly.

I am trying to find a formula how to calculate maximum permissible torque or stripping torque of thread in aluminum (not a bolt).
My connection is steel bolt M7x1 and thread M7 and aluminum housing (Rm - Tensile strength = 240MPa, Rp0.2 0.2% proof strength = 140MPa)

I did not find a formula which include different types of materials e.g. aluminum.
Thank you for your advice.

RE: Maximum torque of aluminium thread

I tryed to calculate the torque, can you tell me where I made mistake?

Housing thread = M7
Lenght of aluminium thread = 9,3mm = 0,0093m
Rm - Tensile strength = 240MPa
Rp0.2 0.2% proof strength = 140MPa

Steel bolt = M7x1

Stress area:
S=2*pi*r*l = 2*3,14*0,0035*0,0093 = 0,0002044 m2

Stripping force:
F/S = Rm --> F = 240*10^6*0,0002044 = 49059,36 N

Stripping torque:
M = F*0,5*d = 49059,36*0,5*0,007 = 171,7 kN

The 171,7Nm is unreal result. Process measured stripping torque is 17-18Nm.

Thank you for your advice.

RE: Maximum torque of aluminium thread

I wouldn't use Ftu, maybe Fty ... but then its a shear failure (I think) so ... ?

I would not use the full thickness, three threads is a typical assumption.

Why do you want the torque to strip rather than a torque to install (1/3 of the steel bolt torque) ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: Maximum torque of aluminium thread

Hi Green strand

The stress area's you are using are incorrect, that stress area that you have calculated is for the whole cross section of the bolt. the are you need is the shear stress area of the aluminium thread. In addition the threads fail in shear and so you cannot use the value of tensile strength without multiplying it with a factor usually taken around 0.7.
have a look at this site under the heading of screw thread area's. The M7 thread is a non standard size so you will need to calculate the appropriate area's.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: Maximum torque of aluminium thread

I think you misread ... he has pi*d*t (not pi*r^2)

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

RE: Maximum torque of aluminium thread

Are you trying to determine installation torque, or required thread engagement/housing thickness, or ????

RE: Maximum torque of aluminium thread

Machinerys' Handbook has an excellent treatment of screw threads in dissimilar materials, with most of the data needed to do the calculations. The female thread is sized to exceed the strength of the male threaded member, generally a bolt or stud. You generally want the bolt to break rather than the thread to strip.



The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: Maximum torque of aluminium thread

green stand

I can tell you that I use to fix aluminum tooling plate all the time for strip threads.
aluminum will gall, corrode, because of dissimilar metals, will seize and strip out.
to prevent spark plugs from seizing on aluminum heads I would use anti seize. but no guaranty.
every time it has to be disassemble there is a chance it will gall. it's better to use
either Heli coils, or inserts.

RE: Maximum torque of aluminium thread

There are many standard fastener torque charts online.

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! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close