Shearing stress calculation for thread 1

[salmon2]

Trying to calculate the shear stress for thread, want to understand a bit more behind the formula.

Basically the shearing area is calculated as:

Area=0.5*Pi*d*L

where d is pitch diameter and L is engagement length. What is the meaning of 0.5? Where does it come from? To me, should be no 0.5 in theory.

 

[desertfox]

Hi salmon2

Try this site:-

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

desertfox

 

[dgallup]

I believe the .5 is because half the material is cut away by the thread.

 

[salmon2]

Bingo, gallop, I think u r right.

 

[salmon2]

Desertfox, thanks for the website, it is very informative.

 

[XL83NL]

A very nice Mechanical Engineering site, mostly based on tribology, containing loads of useful calculators;

http://www.tribology-abc.com/sub9.htm

Here, you'll find several calculators for determining e.g. required thread length, boltening torque. Although youre exact question isnt really clear to me, Im sure you'll find your answer on this website. The book by the Dutch author A. van Beek is really good too, from a mechanical/tribological point of view.

Hope this helps.

 

[Tmoose]

The load distribution in a screw thread is normally considered to look something like this.

http://www.fastenal.com/web/services/engineering/articles/images/load-distribution.jpg

I guess it makes me hesitant to assign "a" shear stress to the thread. The first thread of the 6 threads is going to be loaded at 2X the average. Threads 4, 5, and 6 are under loaded. The loading varies from the values shown progressively around the screw. The portion of the female thread before the first full thread (Thread 1) might be strained even higher, yet not carry that much of the load.

I just use 1.5 diameters of engagement and torque to the appropriate value in some table or another.