# Tied Contact (/INTER/TYPE2)

Interface TYPE2, also called tied interface is a nodal constraint to rigidly connect a set of secondary nodes to a main surface. The secondary nodes forces and moments are transferred to the main nodes, and then secondary nodes are positioned kinematically according to the motion of the main nodes.

This interface ensures a full force and moment equilibrium.
There are four formulations are available to describe this connection.
• Default spotweld formulation
• Optimized spotweld formulation
• Formulation with failure
• Penalty formulation

## Default Spotweld Formulation

Spotflag=0
When the flag is set to 0, the spotflag formulation is a default formulation:
• Based on element shape functions
• Generate hourglass with under-integrated elements
• Give a connection stiffness function of secondary node localization
• Recommended with fully-integrated shells (main)
• Recommended for connecting brick secondary nodes to brick main segments (mesh transition without rotational freedom)

## Optimized Spotweld Formulation

Spotflag=1
When the flag is set to 1, the spotflag formulation is an optimized formulation:
• Based on element mean rigid motion
• No hourglass problem
• Constant connection stiffness
• Recommended with under-integrated shells (main)
• Recommended for connecting beam, spring, and shell secondary nodes to brick main segments

## Formulation with Failure

Spotflag=20, 21 and 22

Using these options, these two failure criteria can be defined:
Rupt= 0 (independent rupture parameters):
Failure when Max_N_Dist or Max_T_Dist are reached (default)
Rupt= 1 (coupled rupture parameters):
Failure when $\sqrt{{\left(\frac{N_Dist}{Max_N_Dist}\right)}^{2}+{\left(\frac{T_Dist}{Max_T_Dist}\right)}^{2}}>1$

During the computation, a normal stress, shear stress, normal displacement and tangential displacement are computed and compared to the maximum values defined in the interface. As soon as the maximum criteria have been reached, the normal stress and shear stress will be set to 0.

## Penalty Formulation

Spotflag=25

The main goal for interface TYPE2 using penalty method is to tie secondary node to main segment without any kinematic constraints. Using the penalty method may avoid
"INCOMPATIBLE KINEMATIC CONDITIONS"
.