excessive stress after bolt pre-load in abaqus simulation

[opethian]

hi to all
We are try'n to make a thermal analyze aprox. 15 cm long heavy exhaust
Manifold head and part of engine block where the part is attached.
Problem that we encountered recently is excessive preload at the bolt neck.
In the model we have pre-load at the middle section and bolt is ties to engine block from below and there is a contact between the
bolt head and exhaust manifold.
Our questions are;
1 ) what is the possible reason of having 3000 MPA stress value ( is it that important value to care that much )
just for preload step with a preload value of 41600 kN for M10 bolt?
2 ) just for a trial we add a test load as a pressure from the turbo section that causes
Bending on the bolts for any pressure load value our contacts in the model do not converge.
So the solves does not go through the load step after bolt load step .

Although we have tried to change master and slave load definitions and different type of contacts for our contact regions

Unfortunately we did not get a satisfactory result yet.

Contact definition still seem to be a problem for 6.7 version of abaqus
but anyway may be one of the most difficult part of simulation for all CAE programs.
Thanks for you replies.
Write you soon.

 

[MrMyers]

Two things - check your units. Unless my back-of-the-fag-packet calcs are rubbish, applying 41,600 kN to an M10 bolt will result in a stress of around 530 GPa - likely not very realistic.

applying 41.6 kN should result in a general stress of ~530 MPa. You could be getting 3000 MPa due to a singularity caused by the mesh near the head.

What sort of elements/model are you using?