More complex bolt pretension analysis, load sequence in OptiStruct

Altair Forum User

Dear all,

 

I'd like to ask you a question regarding load sequence definition in case of nonlinear analysis.
It's kind of a complex, nonlinear load case which consists of: gravity load, bolt pretension and external load.

 

In the first step I'd like to consider effects related to mass influence (compression of a flange).
After the flange is compressed I'd like to apply bolt pretension and at the end consider external load.

 

There is the tutorial about bolt pretension: 
OS-1390: 1D and 3D Pretensioned Bolt Analysis of an IC Engine Cylinder Head, Gasket and Engine Block System Connected Using Head Bolts

 

What I don't understand is why do I need to specify both CNTNLSUB as well as STATSUB(Pretens) to consider bolt pretension.
Isn't it enough to calculate bolt pretension (as nonlinear case) in one load step and then using CNTNLSUB consider it in the next one?

 

In my case I'd like to have following situation:
Gravity loading results --> transfared to bolt pretension load step --> transfered (gravity +bolt pretension) to the last load step (external force)

 

Should I use STATSUB(Pretens) as it's show in mentioned tutorial?

 

Best regards
Jakub

Rahul Rajan_21763

The specific rules for sequencing pretensioning subcases are as follows:

1.            Pretensioning force (PTFORCE) can only be activated in the new or “fresh” pretensioning subcase for a given section. In other words, subcase with PRETENSION pointing to PTFORCE cannot also include STATSUB(PRETENS) referencing a subcase that had already been pretensioned this section. 

2.            Pretensioning adjustment (PTADJST) may be activated in any of the pretensioning subcases for a given section. The effect of adjustment is cumulative relative to the pretensioning status reached in the respective previous subcase, as referenced by STATSUB(PRETENS). 

In nonlinear path-dependent problems, this sequencing of pretensioning can be combined with continuation of nonlinear subcases, as controlled by subcase command CNTNLSUB, in quite arbitrary combination. STATSUB(PRETENS) controls the sequencing of pretensioning steps and CNTNLSUB controls the sequencing of nonlinear aspects (plasticity, contact with friction, etc.) for quite arbitrary loading scenarios