Abaqus warning with connector elements

[Tinni1]

Hello,

I am performing the post-buckling analysis of a cold-formed steel stud and track assembly that are connected to each other by a self-tracking screw.

In Abaqus, I modeled the screw stiffness using the connector elements. I have defined reference points on the stud and track surface, in the screw locations and connected these points with wire elements following that I have applied the screw stiffness. These reference points may not coincide with the corner nodes of the meshes in the stud and tracks (Based on available literature this is OK and we need not connect the connector elements with the nodes).

While running the analysis, I got the below warning:
*WARNING: AT LEAST ONE OF THE NODES OF CONNECTOR ELEMENT 1 (ASSEMBLY) DOES
NOT HAVE ANY MASS ASSOCIATED WITH IT. THIS COULD LEAD TO AN EQUATION
SOLVER ISSUES (ZERO PIVOTS, NUMERICAL SINGULARITIES, etc.) AND
HENCE TO INCORRECT SOLUTIONS WHEN THE CONNECTOR ELEMENT IS
ENFORCING KINEMATIC CONSTRAINTS (FROM EITHER INTRINSIC, CONNECTOR
STOP/LOCK, or CONNECTOR MOTION). PLEASE ATTACH THE CONNECTOR NODES
TO ELEMENTS FOR WHICH MASS IS DEFINED (SUCH AS ELEMENTS TYPE MASS
WITH A SMALL MASS) TO RESOLVE THE PROBLEM.

Could you please advise, if I need to connect the wire elements with the corner nodes of the meshes, to resolve this warning?

 

[FEA way]

Do the connectors behave (deform and carry forces) as expected ? If yes, it should be fine and you can just consider applying point mass to eliminate this warning message.

 

[g.alshamsi]

How are you defining the reference points? Is your model partitioned at screw locations i.e. does every screw location contain a vertex that you can connect wire elements to? If you don't want complex partitions in your model you can achieve that connections by using mesh-independent fasteners in conjunction with connector elements. Unrelated but since you're trying to simulate self-tapping screws I'm assuming you're using a cartesian connector element?

 

[Tinni1]

Hello,
Thanks for your response.
Yes, I am using cartesian connector elements.
I have not used any partitions.
How to achieve mesh-independent fasteners in conjunction with connector elements, in Abaqus? Is that different from wire connectors?

 

[FEA way]

Check the documentation chapter "Mesh-Independent Fasteners", paragraph "Defining Fasteners Using Connector Elements". In Abaqus/CAE it’s automated and you just have to assign the connector section.

 

[Tinni1]

Great!, Many thanks.

 

[Tinni1]

Hello FEA way,

I am exploring mesh-independent fasteners.

I just wanted to understand, if I want to apply some point mass (As suggested in your first response), should I apply it in the property tab of the edit fastener dialog box? (Picture attached as a ready reference)
[URL unfurl="true"]https://res.cloudinary.com/engineering-com/raw/upload/v1664539541/tips/mesh_independent_fastener_mpevt6.docx[/url]


Also, as I am simulating self-tapping screws, should I apply the mass for the screw here? That would be very small.

Many thanks!

 

[FEA way]

According to the warning message, the mass should be applied to elements to which connector nodes are attached but you can try entering it in the fastener settings window - check if the message disappears then.

 

[Tinni1]

I applied point mass but the Abaqus error came that it is no more supported by Abaqus.

However, usage of the mesh-independent fasteners (instead of wire elements with cartesian connectors) removed the warning of zero pivots.
Many thanks, both!

 

[g.alshamsi]

Are you still getting errors regarding the mass? What do you mean "error came that is no more supported by Abaqus"?

 

[Tinni1]

No, I am not getting any error regarding mass.
That error appeared when in I put a small mass in the edit fastener dialog box, property tab, in additional mass input(below the physical radius, please see attachment in my previous response).Other than zero , no additional mass is supported by Abaqus anymore. That's where the error message came from.

 

[FEA way]

Then try assigning mass to elements to which connectors are attached.