Pretension Bolted Connection

LouisB · 2021-02-22 18:13:50

Hello,

I am trying to simulate a bolted connection with a pretension with the following steps:

1. I pull on one side of the bolt with a traction force and fix the other side from t= 0s to 100s (resnonlin0 in my .mess file)

2. Then I want to put a contact between the nut and the bolt and a tie connection at t=100s until the end of the simulation (200s in my example) to simulate the tensioner release. (resnonlin1 in my .mess file)

The problem is that the first step is working well when I run it independently but when I want to add my contact and my tie connection with the nuts I am getting a "NonConvergenceError" which is giving me some advise that I tried to follow (like increasing the ITER_GLOB_MAXI ...) but I still have this error.

Could someone help me to debug my problem ? give me some advise and/or send me an example that I can study ?

Unclosed a .zip file with the .hdf, .comm and .mess of my simulation.

Regards,
Louis

Attachments:
BoltedCo 2.zip, Size: 1.23 MiB, Downloads: 374

mf · 2021-02-23 07:52:38

Hello,

try the attached example for a start.
1) the TIE must be a DIDI, as it refers to the already tensioned state, not the zero state (untensioned)
2) no need for a contact yet. It would be necessary when you put 2 pieces to connect in between your nuts.
3) I created a partition of the nut on the bolt.
4) it could be even better with just fixing the lower ring-shaped part of the nut--> you'll also get the forces in the nut, now it is rigid because you fix the whole nut.
5) your time frame of 100s or whatever does not make sense because everything is linear (material..). There is no time dependence in the material, also this 'time' in static-nonlinear is just a way of ordering forces etc. It is an artificial simulation time that has nothing to do with real time in the most cases.
Just a little advice for non-convergence: if everything is linear and convergence is hard to reach, there is for sure something wrong in the definition of the model (conflicting BCs, moving bodies, or 'rattling' contacts in non_linear etc.). If convergence is not reached within 10-20 iterations, it probably never will. It is easy to see with RESI_GLOB_RELA, if it starts at ~10^⁻12-->good, if it starts at 1-->bad,

Mario.

Last edited by mf (2021-02-24 07:58:22)

Attachments:
StudyF.zip, Size: 1.42 MiB, Downloads: 437

mf · 2021-02-23 13:06:28

Hello Louis,

the above posted .hdf is SM2020.

Here are .med (in .med 3.3 not 4.0 as in SM2020) and .comm. Let me know if you can import it in SM2019. Both files need to be imported separately,

Mario.

Last edited by mf (2021-02-23 13:11:19)

Attachments:
CurrentCase.zip, Size: 686.17 KiB, Downloads: 400

LouisB · 2021-02-23 17:48:47

Hello Mario,

Everything is working with the .comm and the .hdf file.
Thank you for your help.

Louis

alealbanesi · 2021-02-25 21:24:07

Hi, I have some questions on using bolts with a preload in Code_Aster. I have been reading many posts in the forum and testing some examples. Apparently, there are many ways to simulate a preload or tightening in a bolt.

I have two steel plates that are connected one on top of the other by 4 bolts. The bolts don't have nuts, the threads are glued with LIAISON_MAIL on the lower plate. I am using contacts with a Coulomb coefficient.

* One option is with AFFE_CHAR_MECA - PRE_EPSI. For what I've read, this is a pre-deformation. However, I don't see that the steel plates are pushed or pressed together as expected on a preload.

* Another option I found is using CREA_CHAMP - TYPE_CHAM='ELNO_SIEF_R'. However, I suspect that this creates a stress field compatible with the preload, but it is not a preload. Again, I don't see that the steel plates are pushed against each other.

* Another is with AFFE_CHAR_MEC_F, and LIAISON_GROUP. I have not tested this option but is in one of the tests on the Code_ASter web page.

Can anyone tell me if one of these options will create pressure between the plates? Which could better suit my need?

Thank you in advance,

Alejandro

mf · 2021-02-25 22:24:09

Hi Alejandro,

it depends on what you are interested in. My calculations sometimes involve many bolts (up to 30 with different diameters and pretensions). Therefore I only model the bolts with POU_D_E. I apply a pretension with a CREA_CHAMP and then create an ETAT_INIT. The ends of these bolt elements are then glued to the parts to connect. In this example, as it is, 2 STAT_NON_LINE are not needed. But creating it like this gives flexibility, as in the second STAT_NON_LINE you could change the fixation etc... you can do what you want with it, even thermal expansion.
With this type of calculation you will only get one single value of tension in a bolt, you will not get a stress distribution. But this can come in handy also: it is, on the other hand, very easy to study the evolution of the bolt tension if you subject your bolted bodies to any kinds of loads. See attached example, every bolt consists of three groups:

1) 1D line group for bolt element
2) a 0D group that is glued to the underhead group (2D) in your first part
3) a 0D group that is glued to the thread group (2D) in your second part

If you are interested in 'realistic' bolt tensions you should design these groups (create partitions on your bodies!) with the right sizes according to the international standard of your bolt and apply the tension as regulated by this standard (e.g. VDI 2230 is a very good german standard). The length of the bolt element equals the 'free' length of the bolt. That is the length of the bolt shank that is NOT screwed in, only this way your bolt elongation will be 'correct'. The attached example is an example of such a connection, but it's a stupid example because it is a very poorly designed connection (you should never connect 2 bodies like this :-) ). Pay attention to how the bolt relaxes in t=1, so the before applied pretension is lowered by the bodies being pulled together. In this example the pretension drops from 163kN (DIN 8.8 M24 bolt) in t=0 to 127kN in t=1 when they relax.

If you are interested in the stress distribution WITHIN the bolt you should model the bolt (in 2D or 3D) itself, so it will be something similar to the above example,

Mario.

Last edited by mf (2021-02-25 23:10:12)

Attachments:
TEST51_BOLTED_BODIES.zip, Size: 887.31 KiB, Downloads: 475

alealbanesi · 2021-02-25 23:46:51

Thank you Mario for your reply and example. I will look into it now.

I'm modeling the bolts as 3D solids because I'm interested in stress distribution. The preload stress is a 75% fraction of the material yield stress. Your right, it is time-consuming not only the geometrical setup (dividing geometry and mesh) but also the nonlinear solver execution. The PRE_EPSI option required dividing the volume mesh of the shank part of the bolt to assign the negative pre-deformation.

I will try your example, and see the effect on the steel plates. Perhaps I am not being careful with the time-steps.

Kind regards,

Alejandro

alealbanesi · 2021-03-01 12:32:18

mf wrote:

If you are interested in the stress distribution WITHIN the bolt you should model the bolt (in 2D or 3D) itself, so it will be something similar to the above example

Hi Mario,

I've studying and testing your files, it is very interesting and helped me a lot. One of the key aspects is the correct use of the time-stepping, so that loads and pretensions are correctly assigned to the model.

I never used DEFI_CONTACT as in your file, I will give it a try. I assume that the COEF_PENA_CONT is imposed so that the bodies do not penetrate one on the other. I've read in the forum that the value of this coefficient is some orders of magnitude higher than the Young modulus, which is the case in your example.

Since your bolts are Euler beams, and the ends are glued to the 3D bodies, there is no need to model contact between the shank of the bolt and the hole, right? In the case of 3D bolts, this contact should be considered or at least replaced with LiASION_MAIL and 'DNOR' option.

I assume that as your modeling the bolts as Euler beams, the pretension is a CREA_CHAMP with TYPE_CHAM='ELGA_SIEF_R' and NOM_CMP=('N', ) (N if for normal I think). In case that the bolts are modeled like 3D solids, which CREA_CHAMP will be the equivalent to your example?

This pretension is then used to create an initial state ETATINIT, that is applied in INST=0.0 of resnon1.

In resnon2, the load CHARGE=glueBOLT is of the type TYPE_CHARGE='DIDI', I've read above that this is to consider the stressed state of the material.

Is this analysis correct? Thank you for your help,

Alejandro

Last edited by alealbanesi (2021-03-01 12:36:43)

mf · 2021-03-01 14:51:40

Hello,

you're welcome. This way to model bolts has proven to be relatively economical and also quite accurate (of course this is generally questionable with bolts, as tightening bolts with a torque wrench is +-50% off in bolt tension in real life. There are BETTER methods to tighten bolts, also it is very dependable on the lubricant used! Thus, in real life, it is a guessing game....).

COEF_PENA_CONT: ~element_size*E is my starting value, it does not happen very often that I have to change that. It depends on the model itself (gaps, shape of contacting surfaces) though.

DEFI_CONTACT instead of LIAISON: I never tried, my models are too big. Could be worth testing, I think. I assume my bolt connections are a bit too stiff, thus bolt tension is overestimated a bit (gives some safety).

CREA_CHAMP for 3D bolts: there is no easy way like with the beams, I think. That's the dilemma with 3D bolts: you would have to cut them in half and pull on each half. Also, other calcs are not possible (or at least VERY difficult, e.g. thermal expansion because a simple DEPL to pull on the bolt halves would also have to thermally move somehow to keep the expansion 'correct'). Thus, the beams! Also, it is easy to evaluate if and how the bolts are loaded in a Haigh-diagram of the bolt material.

INST=0 pretension: Absolutely correct.

DIDI: Correct, as I understand it (the translation in the manual is quite difficult to understand). I just tested, somehow it does not make a difference here... not sure why. However, it is a remnant of a thermally loaded bolt calculation. If I remember correctly, it was necessary there.

Mario.

Last edited by mf (2021-03-01 15:40:50)

alealbanesi · 2021-03-02 20:02:25

Thank you Mario.

I'm about to test all this in my model. I'll let you know what happens.

Regards,

Alejandro

alealbanesi · 2021-03-15 15:07:07

mf wrote:

The attached example is an example of such a connection, but it's a stupid example because it is a very poorly designed connection (you should never connect 2 bodies like this :-) ). Pay attention to how the bolt relaxes in t=1, so the before applied pretension is lowered by the bodies being pulled together. In this example the pretension drops from 163kN (DIN 8.8 M24 bolt) in t=0 to 127kN in t=1 when they relax.
Mario.

Hi Mario, thank you for your example, it helped me a lot. I got my bolts configured as Euler beams now, and things are working just fine!

Bolts are working ok, the stress level is correct, and I can see the relaxation in the intermediate time-step. Printing the results in a text file is also very useful!

I had some trouble with thermal loads on the beams (this is something that I also found in an older post made by you). With the help of Johannes, I managed to solve that part of the problem.

Thanks for the great help, regards,

Alejandro

mf · 2021-03-15 17:36:56

Hello,

well, that's good to hear. I'm glad it worked out.

Nevertheless beware, your part model must also be absolutely precise (contact surfaces!) if you are interested in the relaxation etc. However, there is always the lame excuse with the tensions tolerance being very high in real life unless you test your bolts on a bolt test bench with YOUR lubricant (F1 engine people do that all the time) or you tension them with some kind of hydraulic device (this is done on very large bolts with >D50 or so and above),

Mario.

Last edited by mf (2021-03-15 17:37:35)

#1 2021-02-22 18:13:50

Pretension Bolted Connection

#2 2021-02-23 07:52:38

Re: Pretension Bolted Connection

#3 2021-02-23 13:06:28

Re: Pretension Bolted Connection

#4 2021-02-23 17:48:47

Re: Pretension Bolted Connection

#5 2021-02-25 21:24:07

Re: Pretension Bolted Connection

#6 2021-02-25 22:24:09

Re: Pretension Bolted Connection

#7 2021-02-25 23:46:51

Re: Pretension Bolted Connection

#8 2021-03-01 12:32:18

Re: Pretension Bolted Connection

#9 2021-03-01 14:51:40

Re: Pretension Bolted Connection

#10 2021-03-02 20:02:25

Re: Pretension Bolted Connection

#11 2021-03-15 15:07:07

Re: Pretension Bolted Connection

#12 2021-03-15 17:36:56

Re: Pretension Bolted Connection

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