Tighten bolt beyond yield point - Preload the bolt in the plastic area 2

[KenoFr]

Hello everyone, I'm new here, let me quickly introduce myself.

I'm a research engineer, and I'm working on "the behavior of an assembly subjected to tightening beyond its elastic capabilities"

To do this, we will carry out tensile tests with different stages of pre-load/tightening. However, before starting all this, I'm looking for articles on the tightening of bolts beyond their elastic limit and haven't found many. It's been about a month now that I've been searching, and apart from a small list of 9 articles, I have nothing else. So, if anyone has information/articles on this subject, I would be happy to discuss it with you.

 

[dik]

I'll rely on my own understanding of things...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[r6155]

In the shop, how can you know if the desired bolt tension has been achieved?

Regards

 

[desertfox]

Hi r6155

You can’t be 100% sure unless you strain gauge measure it or use a tensioner

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[r6155]

Thanks, desertfox
The strain gauge must be in contact along the entire length of the bolts. The elongation is correct and easy.
Ultrasonic is best practice for 25mm diameter studs. and more, and no length limit.
I'm not sure about many of the papers we see.
My intention is for best practice during installation (not in the lab) in the field.
I had a good experience with elongation control, on nuclear components.

Best regards

 

[desertfox]

Hi r6155

Actually the strain gauges don’t have to contact the bolt for the whole length, typically cylindrical strain gauges are bonded to the bolt or screw through drilling a small blind hole through the centre of the bolt head and down into the shank after which the strain gauge is inserted. If you Google measuring bolt elongation with strain gauges you see what I mean

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[TugboatEng]

The strain gauge portion of the bolt will have controlled diameters to produce predictable results. Ther is no need to instrument the entire length.

 

[r6155]

But this is for lab work, not production work.
Example: pressure vessel with 36 studs d=76 mm x L= 700 mm with strain gauge?

Regards

 

[cherish]

Hi desertfox,

The joint in this example has value of load sharing ratio of 0.19, so bolt will feel 19% of external load in additional to preload as long as joint is not seperated.

Diagrams of test 4 (external 85 kN and 120 kN)with a scaled view for load case has external load 120 kN:

In common sizing of bolt on the safe side and to avoid finding stiffness of the joint, limit external load maximum up to preload value is selected. However, some applications like lifting, available threaded holes can be used is quite limited and therefore utilizing bolt capacity as much as possible will need for finding joint stiffness...

In case preloaded at 70% yield for 8.8 & 10.9, with external load equals to preload:

Engineering is a journey of thousand miles begins with a single step

 

[r6155]

The numbers, the graphs... are pretty. But in manufacturing things are different.
I worked with reactor pressure vessel (nuclear): 76 studs M220 mm x L= 2500 mm 850 kg each, all tensioned at the same time.

Regards

 

[desertfox]

Hi Cherish

Thanks I’m with it now .

Hi r6155
I don’t think the OP is after what’s done in the field, I believe he/she is looking for theoretical information reading his original post. What happens in the field is as you say completely different to a laboratory.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Stress_Eng]

On a pure theoretical / investigation basis, my interest would be how the thread axial load distribution changes as increasing preload increments progressively makes the first and subsequent threads yield and go plastic in the highly stressed regions. Test results for both static and fatigue would be interesting to see.

 

[KenoFr]

Hello everyone, to clarify things, I'm looking for information in the literature on tightening bolted assemblies in the plastic field, indeed as some discuss here sometimes it is beneficial to tighten an assembly in the plastic field. Here are a few references where authors were able to demonstrate this result through pure tensile tests: [Chapman et Al, 1986], [Yamashita et al., 1985], [P. J. Gill, 1975], [Nagata et Al, 2009].

For my part, I'm looking for additional articles because in the coming months I'll be carrying out pure tensile tests to determine whether clamping in the plastic zone has a beneficial effect or not, and I wanted more information so that I'd know what to expect or what to compare myself with.

 

[Tmoose]

"I'll be carrying out pure tensile tests"

Tests of bolted assemblies?
Tested to joint separation?
Fatigue?

 

[KenoFr]

Pure tensile tests on bolted assemblies, firstly to characterize my screws, in order to identify the elastoplastic behavior law of the screw material.

Secondly, fatigue tests.

I'm going to do this with different tightening levels:
75% Re
Re
Re + 30% (Rm-Re)
Re + 60% (Rm-Re)
Re + 90% (Rm-Re)

→ 3 fatigue tests per tightening level
(15 tests)

 

[desertfox]

Hi KenoFr

What about the clamped materials? Whatever materials you intend to clamp will affect how much you can tighten the bolt, surely you have to take account of the clamped material properties in terms of there stiffness, hardness etc[pre][/pre]

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[KenoFr]

We're going to clamp a traditional steel assembly. For the bolts, we'll be using stainless steel and traditional steel.

If you're interested, I'll be back here in a few months to discuss the results with you.

 

[desertfox]

Hi KenoFr

Yes will be interesting to hear what you find.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[dik]

Let us know... this has been one of the more interesting posts of late.

The old expression, "Tighten 'er until she cracks, then back off half a turn, comes to mind."

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Stick.]

I'm pretty interested in the results, particularly how stainless compares to carbon steel, given the differences in stress/strain curves between the two.

 

[Double-Edged]

For some interesting reading google search:

"torque to yield bolt"
or
"Torque-to-yield bolts"

Typically used in high cyclic loading applications.