Learning Forum

[clarababymangalath]

Hi everyone,

I am trying to model two bodies with a frictional contact in LS-DYNA, so that, when the body on top is pulled (force increases from 0N at 0s to a value F over a period of time say 2s or 5s), no displacement occurs until resistive force (coeff of static friction*normal force) is reached. This is my basic goal.

I first modelled these two bodies and didn't define any contact. But on running the simulation, the top body moved as if its a zero friction case. That is, it moves just as force starts to increase. No normal force to the surface or gravity is acting in this case.

Then I defined 'Automatic_surface to surface' with no friction, no gravity, or no normal force. Just the pulling force is acting. But now, after running the simulation, the displacment is there right from the begining as expected but is in the range of e-6m which is really negligible. Like there is no movement at all compared to the previous model with no contact defines at all. It seems as if the contact type kind of glued them together.

I tried again by inputing some friction and gravity to this model. But then displacement became to a range of e-5. There is something that is seriously wrong.

I am not able to identify what is going wrong here. It is such a simple model that I want and am not sure of somethings.

Is this the right contact model to use in this situation? Why is that with 0 friction the body on top is still not moving ? or is there any other problems to this model that striked you on reading this?

[igandiko]

If this behavior is due to *CONTACT then forces in RCFORC (*database) would reflect the force applied to the block. nPlease check if the bc's are defined correctly. In the contact card, you can try setting soft option with sbopt=4 or try using automatic_nodes_to_surface contact.

[clarababymangalath]

Hi,nI tried all these suggestions, like changing boundary conditions setting SOFT and SBOPT. I also tried several contact types including automatic nodes to surface. This doesn't seem to resolve the problem. With nodes to surface contact, inspite of applying gravity, frictional force is not coming into effect and the top body flies away. The frictional energy is 0, which shows again its not in effect yet.