## General Mechanical

Topics relate to Mechanical Enterprise, Motion, Additive Print and more

#### Deformation of a simple bolt connection with bolt pretension

• Tim Dietl
Subscriber

Hello everybody, I want to measure the total bolt deformation of this connection and I don't know how. I hope you can help me.

The Problem is the bolt pretension which compresses in ansys the clamp length to simulate the preload force.

I thought that I can just measure deformation in y-direction from the two surfaces and take the average value of it and then substract then from each other to get the total deformation in y-direction.

Well this dosesnt work. Calculation says that the whole bolt should have a deformation of about 0,1429511mm.

Because of the bolt pretension the clamp length gets compressed and I can't measure the real deformation.

Any ideas?

• peteroznewman
Subscriber

Drag the Bolt Pretension boundary condition and drop it on the Solution branch. That will create a Bolt Pretension result.  The result shows you the Adjustment Reaction in mm and the Bolt Pretension in N.

In the image below, the bolt was tightened in Step 2, but that usually happens in Step 1.

It looks like the bolt shank body is already split at three planes.

Which face is the one where the threads on the shank first touch threads in a hole?

The shank length L that gets stretched goes from just under the head to the plane where the first threads start in the hole.

The face on which you applied the Bolt Pretension load will automatically split the shank in half to apply a displacement (Adjustment Reaction) between two new circular faces to create the Bolt Pretension F. The pretension force F stretches the shank length L to give the Total Bolt Deformation = FL/AE where A is the cross-sectional area of the bolt and E is the Young's Modulus of the bolt.

• Tim Dietl
Subscriber

When the red face ends, thats the point wher the threads on the shank touch the threads in the hole.

First step: bolt pretension

second: working load ( 5,5MPa Pressure)

Here it says adjustment reaction: 0,1736mm.

And deformation = FL/AE = 48458N*42mm/(2*10^5MPa*PI/4*12^2) = 0,089977mm

I am confused?

• Tim Dietl
Subscriber

Calculation says that the whole bolt is supposed to have a total resilience of 2,95*10^-6 mm/N so that would be a total deformation of 0,1429511mm.

• peteroznewman
Subscriber

Adjustment is the total displacement needed to stretch the bolt, compress the flange material and deform the head and threads.

The equation FL/AE is only the stretch of the bolt shank, so the difference between bolt shank stretch and adjustment is for the other deformations.

• Tim Dietl
Subscriber

So adjustment is equally to the total deformation of the bolt? But why says calculation 0,1429511mm?

• peteroznewman
Subscriber

What calculation says total deformation of the bolt is 0.14295 mm?  What is the definition of "total deformation" of the bolt?

I gave you an equation for the stretch of the bolt shank and it is very easy to understand the physics of why it is correct.

• Tim Dietl
Subscriber

VDI 2230 says that the bolt is supposed to have a resilience of 2,95*10^-6 mm/N which equals a total  deformation of 0,14295mm. (Preload force is 48458N)  resilience*Force= deformation.

My goal is to measure that deformation of the bolt in ansys so that I can compare the value with different mesh sizes.

Do you know what I mean?

• peteroznewman
Subscriber

I haven’t read VDI 2230 so I don’t know how the bolt stiffness value was determined.

I will add in another contributor to the Adjustment total that I didn’t mention above: Penetration in Frictional Contacts. As you can see in the image below, this model has some Penetration that could be reduced by adjusting the stiffness of those Frictional Contacts.

• Tim Dietl
Subscriber

What value for penetration tolerance would you recommend? Or do I have to change the friciton coefficient for that?

• peteroznewman
Subscriber

In the Details window for the Frictional Contact is an item called Normal Stiffness which is set to Program Controlled. Change that to Factor and then set the Factor to 10 (the default is 1). This should make the penetration about 10 times smaller, but it will require more iterations to get there.

This has nothing to do with the friction coefficient.

• Tim Dietl
Subscriber

Thank you! It looks better know.

• Tim Dietl
Subscriber

Why is value for bolt pretension increasing when the mesh size gets smaller?

• william Lucking
Subscriber

Larger elements stend to be a little stiffer in general.

• peteroznewman
Subscriber

I agree with Mr. Lucking. Smaller elements are more flexible than larger elements so a 1% increase in adjustment is required to maintain the same bolt pretension force.

• Tim Dietl
Subscriber

Okay that would make sense. Thank you!