Threaded Inserts - load into member 1

[dag113]

I have a joint comprised of a bolt, a washer, a steel plate, and an aluminum plate. The aluminum plate contains an MS51830 threaded insert; the bolt is threaded into the insert. A specified torque is applied to the bolt to clamp up the joint.

I can calculate the preload developed in the bolt by using:
T = kFD,
where T = torque, k = coefficient of friction, F = preload, D = bolt diameter.

My question (which may be insanely simple but I've gotten myself wrapped around the axle overthinking things) is: is the axial load between the insert and the aluminum plate the same as the preload developed between the insert and the bolt?

(Ultimate goal: check the threads of the aluminum member and ensure they won't strip under loading.)

Also, if anyone has any sources for "threaded inserts calculations," I'd be very grateful.

Thank you very much for any help you could provide in straightening me out!

 

[desertfox]

Hi dag113

Yes the preload in the bolt is the same as the clamping force holding the components together, however and maybe this is what your thinking, the stresses in the thread will be different than those in the aluminium and steel plate.

http://school.mech.uwa.edu.au/~dwright/DANotes/threads/preload/preload.html#top

http://www.roymech.co.uk/Useful_Tables/Screws/Thread_Calcs.html

http://www.roymech.co.uk/Useful_Tables/Screws/index_screws.htm

these sites might help

desertfox

 

[drawoh]

dag113,

I just Googled MS51830. Your fastener is known commerically as a Keensert. You should be able to search for and find manufacturer's literature telling you how strong the fastener is.

JHG

 

[dag113]

Desertfox and Drawoh,

Thank you both very much for your replies, as well as for the fastener links.

My issue really isn't the keensert but the threads on the aluminum plate where the insert is installed. When the bolt is installed into this joint (torqued into the insert in the Al plate), do the Al plate threads see a load equal to the preload (clamp load) applied by the bolt?

E.g., if T = 60 ft-lbs, k = .15, and bolt d = .5,
Preload = T/(kd) = (60 x 12)/(.15 x .5) = 9600 lbs.

So, 9600 lbs. is the load that the bolt and the internal threads of the insert sees. Now, do the external threads of the insert and the threads of the Al plate also see that same load? Or is it possibly less because now we would use .625in. as the diameter (external diameter of insert)? Or less for some other reason, such as how the members of the joint (the two plates) are compressed due to the preload?

Again, thanks for the replies and to anyone else who might chime in here to set me straight.

 

[desertfox]

Hi dag113

The external threads on the insert in the aluminium plate see the pre-load of the bolt, however because the external thread of the insert has a larger area than the internal threads, the stress on the external threads is less.

 

[dag113]

Thanks again, Desertfox. That was what I thought (before I started overthinking; very bad habit). Yes, the stresses drop down due to the increased diameter, but my aluminum plate is the weak link in this joint and the bigger diameter doesn't buy me enough to make up for the low material strength.

Thanks for the help.
Dag

 

[drawoh]

dag113,

I have never tried to engineer Keenserts.

If you make any kind of an effort to look up helicoil thread inserts, you will find a table showing the required length of the insert in various materials that ensure a given screw will fail in tension. The Keenserts almost certainly have a table like this too.

JHG