Subcase for Pretension Analysis

Hello,

I want to perform a step-by-step analysis as in the tutorial below.

That is, firstly, I want to tighten the ring with SPCD and then torquing the bolts. For this scenario, can't we do a preload to the pretension step? (You can think of this process as elastically deforming the ring with the press and then fixing the position with a screw.)

https://2020.help.altair.com/2020/hwsolvers/os/topics/solvers/os/contacts_and_pretensioning_bolts_os_example_r.htm?zoom_highlightsub=CNTNLSUB

Thank you.

Best Regards,

Ovunc

S_S_VER02.hm

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PaulAltair

Yes, you ought to be able to do that, you might need to use LGDISP and MODCHG (to activate/deactivate contacts) depending on the geometry, e.g. in the mocked up example you have made, the bolt head contacts need to be off in the first case and then on in the second

Ovunc

Yes, you ought to be able to do that, you might need to use LGDISP and MODCHG (to activate/deactivate contacts) depending on the geometry, e.g. in the mocked up example you have made, the bolt head contacts need to be off in the first case and then on in the second

Hello @Paul Sharp,

Firstly, thank you for support. I did't know MODCHG. This information has been very useful for me. Thank you again.

I made the additions you mentioned. In the example I created, the two steps seem to work independently of each other. So, I couldn't add preload to pretension step.

Could you please examine model?

Thank you.

Best Regards,

Ovunc

S_S_VER03.hm

PaulAltair

Hello @Paul Sharp,

Firstly, thank you for support. I did't know MODCHG. This information has been very useful for me. Thank you again.

I made the additions you mentioned. In the example I created, the two steps seem to work independently of each other. So, I couldn't add preload to pretension step.

Could you please examine model?

Thank you.

Best Regards,

Ovunc

It looks to be working ok I think... the preload is effectively much much higher then your pretension, so the bolts just stretch back due to the preload

It is clearer to understand if you add 'NLOUT' requests to the 2 steps (NINT 10), then you can view the transient progression of the steps rather than just the start and end points

You are compressing the ring by 2mm and you are specifying an initial overclosure for the ring contacts of .15mm so the compression is effectively 2.3mm so the forces are very high

The attached is a modified version, where I removed the ring overclosure and modified the ring geometry so the compression is only 0.2mm instead of 2mm and it looks much more sensible (I also added NLOUT)

S_S_VER03.fem

Ovunc

It looks to be working ok I think... the preload is effectively much much higher then your pretension, so the bolts just stretch back due to the preload

It is clearer to understand if you add 'NLOUT' requests to the 2 steps (NINT 10), then you can view the transient progression of the steps rather than just the start and end points

You are compressing the ring by 2mm and you are specifying an initial overclosure for the ring contacts of .15mm so the compression is effectively 2.3mm so the forces are very high

The attached is a modified version, where I removed the ring overclosure and modified the ring geometry so the compression is only 0.2mm instead of 2mm and it looks much more sensible (I also added NLOUT)

Hi Paul,

Thank you so much.

Best Regards,

Ovunc