Bolt Extension

[daparojo]

Just a quick cry for help.
I have a bolt that is subject to a load hydraulically, so in that I know precisely what the loading is on the bolt.
Once stretched, the nuts are locked and the pressure released.
Obviously, the bolt has extended slightly to retain the load. I need to double check the theoretical compared to the actual results. Could someone help in guiding me to the calcs to work the theorectical?
Thanks

 

[PriamEngineering]

you need to calculate the bolt stiffness for a start. Look at VDI 2230. it's quite deatiled in this respect.

Bickford is also useful and gives the calculation as

L = PL*(1/Kb)

where
L= change in lengh
PL = Preload
Kb = bolt stiffness

good luck

http://www.priamengineering.co.uk

 

[desertfox]

Hi daparojo

You can estimate the amount of elongation of the bolt assuming thats what your trying to check

x= P*L/A*E

x = change in bolt length

L = original bolt length

A = area of bolt cross section (you may want to use the pitch dia to get this area)

P = known preload

E = modulus of elasticity of bolt material

desertfox

 

[MintJulep]

It's common to apply desertfox's formula to the threaded and unthreaded lengths of the bolt separately, using different areas.

 

[daparojo]

cheers guys

 

[tbuelna]

daparojo,

You'll need to consider the stiffness of both the fastener assembly and the clamped structures in your analysis.

If you want to have an accurate validation of both your analytical model and your fastener installation process, you should check the strain of an installed fastener. Or better yet, a statistically relevant sample of several installed fasteners. This can be done by careful dimensional measurements of the parts, or by other methods such as ultrasound:

http://www.gammatecsa.com/-bolt-tension-monitoring-

Good luck.
Terry

 

[desertfox]

As I understand the OP post, he is using a hydraulic tensioner to tighten the joint, what he requested having already estabilished the axial load on the bolt was a check on the bolt elongation which I believe my formula provides.
He is not trying to analyse the joint as I see it otherwise I would agree about considering flange stiffness.

http://208.106.143.171/Portals/0/pdf_docs/HowItWorks_Tensioning.pdf

desertfox

 

[desertfox]

In a nut shell what I was trying to say that the OP already as the tension force of the fastener which should include a "load Transfer Factor" for transfering load to nut and flanges etc

see this link:-

http://www.group-vector.com/Media/SPO-Installation&Assembly.pdf

 

[unclesyd]

As a friend of the this thread questions abound. Agree that the information as given is correct, but the OP can get into trouble if this joint has a large bolt spread and he is using only one tensioner, he doesn't specify. I've seen it too many times where one tensioner is tried and not worked.
Knowing the physical parameters of the bolted connection would be interesting such as number of bolts, pattern, size and operating conditions.