Learning Forum

[Tiisora]

Hi everyone, 

I'm a student and I'm learning about LS-DYNA.

I'm simulating a drop test, where Part 1 is falling onto Part 2.
Part 1 is only assigned gravity, and Part 2 is fixed in all 6 degrees of freedom.

After Part 1 starts interacting with Part 2, Part 2 disappears after a short period of contact.
Does anyone know what might be causing this?

One notable point is that Part 2 is assigned a soft material.
At first, I used MAT_057 (MAT_LOW_DENSITY_FOAM) with 3D solid elements, and the results looked fine.
Later, I changed the model to use 2D shell elements.
I noticed that MAT_057 gave errors with shell elements, so I switched to MAT_181 (MAT_SIMPLIFIED_RUBBER/FOAM) and that’s when the issue started.

Thanks a lot in advance!

[Dennis Chen]

Hello, maybe check on your log file or d3hsp file to see if you notiiced any messages around elements being deleted.   Also check what constraints the target. 

Another thing you can do is to set one run with max # of cycles to something like 10,000 in control_termination and then set database_binary_d3plot to something very small so you can see what happens leading up to the issue. 

let me know if this works as some basic troubleshooting steps that one can always use. 

[Raghav]

Hello, you might have to check contacts. Generally, a drop test requires mortat-type contact rather than a surface-to-surface type. Try switching the contacts to check if it works.

Regards

[Tiisora]

it seems like my model has an element error.

At first, I used the CONTACT_AUTOMATIC_SINGLE_SURFACE_TIED contact for Part 2 MAT_181.
then I deleted it and the error was gone.

But when I changed to another part 2 model with more elements and a seemingly worse mesh, it continued to have the above error.

I think the problem is due to the poor quality elements when in contact overlapping each other and creating an error that led to the model disappearing.