### 13.5.1. Verification of Bond Status

You can verify the status of the bonds in your analysis in several different ways, outlined in the following sections.

- Using the Prt File Output
- Using Preprocessing Output
- Using Post Processing Output
- Bonded Contact Warning Messages

#### 13.5.1.1. Using the Prt File Output

Verification of the initialized bonds can be done by inspection of the prt file. A summary is given which lists the number of candidate nodes for bonding and the actual number of nodes that were bonded. If the percentage of nodes to be bonded is 0% it means none of the nodes are actually bonded. Please consider increasing the Maximum Offset in this case.

#### 13.5.1.2. Using Preprocessing Output

In order to visualize the bonds it is possible to use the following advanced procedure. Please note that this is only available in the Autodyn component system and that a backup of your model file at cycle zero needs to be made because beam elements are added to the model to visualize the bonded connections.

1. Define and set the environment variable:

   ATD_GROUPPLOT_BONDED_CONTACT = ON

2. Start Autodyn and open the model (make sure you do this after defining the environment variable).

3. Save your model as, for example, <admodel_db_0.ad>

4. Run the model for 1 cycle.

   This will generate output like:

5. Go back to cycle 0 and import the files via menu: Import -> Import from Nastran (BDF).

6. During import, make sure you select the checkbox Convert Properties to Autodyn Parts.

7. You will now have a new part containing the definition of the bond used in the simulation. If the bonds are not offset it is best to visualize them by activating the Grid tick box under Additional Components and by reducing Opacity of the corresponding parts.

8. In the example pictured here, the black dots visualize the bonds which are the end nodes of tiny beams in this case. Note the two new parts that were created upon import of the dat files.

#### 13.5.1.3. Using Post Processing Output

Additional verification can be done via the element variable BOND_STATUS. It is used to record how many nodes are actively bonded to the faces of an element. This variable can be contoured to verify that bonds are correctly defined. If a bond fails during the simulation the bond status will show a reduction in the number of active bonds. When an element has no remaining bonds the value of BOND-STATUS is set to -1.0.

#### 13.5.1.4. Bonded Contact Warning Messages

During initialization of the bonded connections the solver will do some definition checks because a candidate node can only be bonded to one target face. The solver does allow a face to be the target for multiple nodes, which makes it possible to always resolve the warnings. The warnings may not always be problematic, but it is wise to inspect the model setup to make sure the definition was done properly. Two checks are in place:

- A candidate node can exist in multiple bonded connection definitions. Ultimately the solver will only pick the closest face to the node and disregard all the other faces. If a node is a candidate in multiple definitions the user will be warned in the log-file with the message: "There are n bonded connection(s) that contain the same node(s) in the scoped Contact geometry."

  An example of this is a plate that is bonded asymmetrically between two solid geometries. The nodes of the plate will only bond to one side. In this case it is wise to also (or only) bond the nodes of the solid to the plate. Bonding the nodes of the solid geometries only asymmetrically to the plate will most likely yield the most robust results and will resolve the warning message.

- By default, the maximum offset is defined as 1e-4 mm. This allows bonding when geometry faces are coinciding. In cases where (small) offsets are existing between the faces, this maximum offset will be too small to generate any bonds. If this situation occurs, you will be warned in the log file with a message: "There are n bonded connection(s) where none of the Candidate nodes found a target face."

  Typically this situation can be resolved by increasing the maximum offset. Also, it is wise to double check the scope of both the Contact and Target definition. You may have selected the same face or edge in both the contact and target scope, which results in no bonded contact pairs. A third item to check is the overall definition of all bonded connections. If candidate nodes in the contact scope list are also used in other bonded connections they may take precedence over the definition at hand. In the latter case the message will always co-exist with the message in the first bullet. Defining the bonded connections asymmetrically gives you full control over the bonding definition and will resolve the warning messages in the latter case.

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