Bolt Extension Help

[Daparojo252]

Hi people.
I have a problem in that I need to look at.
I have a bolt that is threaded both ends with nuts on the end. The bolt goes through two coupling halves. The middle portion is bigger in diameter of the thread, a slight clearance in the hole. The bolt is hydraulically tensioned, and then whilst under tension the nut is nipped up to the coupling face.
The pressure is released and the bop tensioner removed. The bolt has a retained load in it which I roughly know.
The thread is 45mm with a small undercut at both coupling faces of 37.5mm dia. and the bolt length is 330.50mm, the hole size is 60mm.
The coupling width is 120mm + 120mm.
The Young Modulus is 210000 N/mm2
The Applied Losd is 750kN
The Retained Losd is 550kN

How can I find the theoretical bolt extension?

Please help

 

[JohnRBaker]

This has the 'smell' of a classroom assignment. Well...

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

 

[desertfox]

Hi

well the extension of the bolt is equal to the compression of the joint, when the joint is first made with its preload, so assuming that the 550kN is the preload and knowing the cross sectional area of the bolt and Youngs Modulus the bolt strain can be found from:-
X/L = E.A/F. Where E = modulus of elasticity
A= bolt cross section

F= bolt preload (550kN)

L = bolt length between the nuts

X = bolt elongation

Once you have calculated the strain multiply it by L to get bolt stretch.

 

[Daparojo252]

John, it's not a classroom assignment. I am trying to put a theoretical equation to a mechanical test.

I tried to implement the equation of

Dl= FL
--
EA

But it seems a little way off, but not much.

F = 750 kN
L = I have turned the whole bolt length, or the clamping length between the nuts ie 240mm
E = 210 000 N/mm2
A = I have tried the thread dia! and the the thread undercut area.

Any help would be appreciated.

 

[Daparojo252]

Thanks desert fox.
The cross sectional area would be the thread dia? Undercut of thread? Or the bolt area in the hole I.e 60mm? Thanks

 

[desertfox]

Hi

I would use the minor diameter of the thread, what sort of accuracy are you looking for on the thread extension.

 

[Daparojo252]

As accurate as possible Desertfox. I am trying to relate some pre calculated figures against actual tensioned figures, and trying to get my head round how the theoretical figures are calculated. What is apparent is that the calculated figure is marginally lower than the actual tensioned figure which is good.
Thanks for your help.

 

[Daparojo252]

Is there anything else that could improve accuracy?

 

[desertfox]

Hi

This might help

http://www.brammer.com.pl/DOWNLOAD/SKF_napinacz_srub_Hydrocam_podrecznik.pdf?download=172