how to calculate shear area on taper thread?

[yudhichen]

Dear folks,

anyone knows how to calculate shear area on taper thread? i'm trying to calculate shear capacity for taper thread.
so far i've only seen shear area determination for straight thread, not taper.
any idea?

thank in advance

yudhi

 

[rb1957]

conservative ... use the minimum area

more realistic ... figure out where the first thread into the nut is, use this area

Quando Omni Flunkus Moritati

 

[tbuelna]

Do you want the shear area along the helical engaged length at the internal or external thread root diameter? For example, the thread root shear area that would be of concern with an axial load applied to the thread joint?

If so, one issue with tapered pipe threads is that since they are tightened to an interference fit the total engaged thread length can vary a bit from one joint to another. Also, due to how the tapered threads are produced, the threads in any given connection may not be equally loaded along the engaged length.

The taper angle in NPT threadforms is just 1:16 per side. So the variation in thread pitch diameter along the engaged thread helical length should not have too significant an effect with a simple shear area calculation.

 

[yudhichen]

my aim is i wanna know the shear capacity of both (external & internal thread) in case axial load applied to the thread joint.
i had some thinking like what rb1957 says for conservative to 'use minimum area'.
but if i calculate it in that way, means that i disregard the advantage of taper thread
(i'm not study it in detail, but i believe taper thread is one of the attempt to improve thread joint connection).

i'm looking for some sample how people determine shear capacity of taper thread (by hand calculation, if possible).

anyway, thanx for reply.

 

[tbuelna]

So it's not a tapered pipe thread that you are asking about, but simply a tapered screw thread in general.

I have not seen an example where a tapered screw thread provided better axial load capacity. But I have seen where the threads in a tapped hole were created with a continuously variable pitch to equalize the stresses in the threaded connection.

 

[hydtools]

Calculate the length of the spiral of the area centerline at the radius of the shear area of interest. Multiply that length by the width of the thread at the shear area of interest to calculate the total shear area.

Ted

 

[hydtools]

See also:

http://books.google.com/books?id=go...#v=onepage&q=length of conical spiral&f=false

Ted

 

[Compositepro]

It should simplify to the same equation as a straight thread, just use the average diameter of the taper.
It also depends on how detailed you want to get. The first few threads will carry most of the load unless you allow for plastic deformation to spread the load.