Bolt Extension
Bolt Extension
(OP)
Firstly, it's a long time since I have calculated this, so I need a little refreshing.
I have a bolt M48 that is in a coupling hole 65 dia. Bolt is xxx mm long.
It is tensioned hydraulically at one end, nut tightened and then pressure released. The bolt has stretch xxx mm
The load is xxx kN
Am I right that the extension would be.
Extension = Force x Effective Lenth Of Bolt
-------------------------------
Youngs Modulus Elasticity x Tensile Stress Area Of Bolt
The bolt is threaded at both ends and from the undercut of thread, the diameter of the bolt increases in the coupling is 1mm less than the hole size i.e. bolt shank
What is the effective length of the bolt, is it the coupling width or the length of the bolt shank?
And what is the tensile stress area? the area of bolt shank, hole or thread undercut?
Thanks
Paul
I have a bolt M48 that is in a coupling hole 65 dia. Bolt is xxx mm long.
It is tensioned hydraulically at one end, nut tightened and then pressure released. The bolt has stretch xxx mm
The load is xxx kN
Am I right that the extension would be.
Extension = Force x Effective Lenth Of Bolt
-------------------------------
Youngs Modulus Elasticity x Tensile Stress Area Of Bolt
The bolt is threaded at both ends and from the undercut of thread, the diameter of the bolt increases in the coupling is 1mm less than the hole size i.e. bolt shank
What is the effective length of the bolt, is it the coupling width or the length of the bolt shank?
And what is the tensile stress area? the area of bolt shank, hole or thread undercut?
Thanks
Paul





RE: Bolt Extension
Where:
DL = Total elongation of fastener (inch)
F = Design preload tension (lbs)
Lb = Bolt shank (unthreaded) length + ½ bolt head height (inch)
Ab = Cross sectional area of the unthreaded bolt shank (inch2)
Ls = Bolt effective thread length + ½ nut height (inch)
As = Cross sectional area of the threaded bolt shank (Stress area) (inch2)
E = Modulus of elasticity of bolt (psi)
RE: Bolt Extension
-------------
-----/ 64mm \-----
48mm 48mm
(Profile)
The bolt is hydraulically load, with nuts on either end. As the bol streteched, the nut backs off slightly, at load, the pressure is held, and the nut tightened. Once tightened the pressure is released.
RE: Bolt Extension
Modify the formula accordingly then.
RE: Bolt Extension
RE: Bolt Extension
Yes your formula is correct altough am I correct in assuming its the 65mm dia thats being stretched and not the 48mm and 65mm as thats a slightly different story.
desertfox
RE: Bolt Extension
The tensioner is on one end and stretches the stud slighly at a predetermined load. Am I right in presuming that the 48mm thread diameter and 64mm diameter will stretch? Or should I base it on the shank i.e. undercut of the stud?
What happens if the bolt is fitted in the coupling
i.e.
Cplg Width
1----1---1
X /----\
---------- 65mm --------
I 48mm 48mm I
I---Y-----I
x=tensioned side
Is the effective length the same as the the coupling width or the length from the end of the stud to where it starts to become fitted i.e. Y?
Also is the stress area now the undercut of the stud?
RE: Bolt Extension
If the tensioner is gripping on the thread then both diameters will stretch in length.
The stud will stretch from the point at which it is anchored ie from the underside of the nut or washer at the point of first restraint.
desertfox
RE: Bolt Extension
desertfox
RE: Bolt Extension
RE: Bolt Extension
I would ignore any bolt length that protrudes outside the nut.
desertfox
RE: Bolt Extension
Cheers desertfox and others, it has refreshed my ageing mind.
RE: Bolt Extension
If I understand your last post correctly it is not good practice to leave the studs inside the nuts, the stud should have full thread engagement within the nut and protrude past the end of the nuts by a minimum of two threads.
desertfox
RE: Bolt Extension
For a stud I suggest half the nut height at each end.
RE: Bolt Extension