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Unconnected Region in Flange Model

Unconnected Region in Flange Model

Unconnected Region in Flange Model

(OP)
Hi,
I'm currently modelling an axi-symmetric flange pair with a single bolt and gasket and having issues with contacts.
The contact pairs specified are:
1) Between the underside of the bolt heads and the upper and lower surface of the flange
2) Between the raised faces and the gasket
3) Between the two flange hubs

The contact properties that are specified are:
1)Normal behaviour with Pressure-Over-closure of hard contact, Constraint enforcement method of default and have allowed separation after contact
2)Tangential behaviour with friction formulation of penalty with a friction coefficient of 0.2.

The boundary conditions constrains the mid-plane of the gasket in the vertical direction.
With this model set-up, I am getting the following issues:
1. An error "There are 3 unconnected regions in the model".
2. Flange hubs are penetrating (despite the contact properties)

I can only seem to overcome this issue by applying tie constraints on the same surfaces as those to which the contacts are applied... However, the model must work without these tie constraints as the flange should separate from the gasket.

Attached is the input file.

Any help would be greatly appreciated!!!
THANKS IN ADVANCE

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