Learning Forum

[panjc]

I'm using lsdyna simulate the rolling process,workpiece rotated about 600rpm and the tool was fixed,the negative volume message was indicated when the simulation starte.I increase the simualtion time,it can be simulated,but its deformation was too large,like the material is soft,but it is aluminium.Actually, there shouldn't be such a big deformation.was it because the rotation speed was too fast?or some settings was wrong?

[Ram Gopisetti]

Hi,

For dealing with negative volume issues please check https://www.dynasupport.com/howtos/material/negative-volume-in-soft-materials and our forum thread https://innovationspace.ansys.com/forum/forums/topic/negative-volume-2/

Cheers Ram 

[Pedram Samadian]

Hi,

A negative volume message in LS-DYNA during forming simulation typically indicates that an element has become so distorted due to extremely large deformations that its calculated volume is negative. You can try the following ways to address this issue:

1- Ensure the mesh is well-structured, with elements having good aspect ratios (ideally close to 1 for quadrilaterals). Use a finer mesh in areas with high deformation (e.g., near punch corners, die entry radii). Overly coarse elements can lead to distortion.

2- Check your input hardening curve cover the expected range of strains.

3- Use a proper contact card with reasonable values for different parameters. The choice of imporper values for contact parameters can result in unrealistic penetrations or excessive forces.You can check the LS-DYNA user’s manual Vol.1 (LSDYNA Manuals) to learn about different contact cards in LS-DYNA. 

4- Reduce the loading step size to allow the simulation to handle large deformations more accurately. Ramp up the input load or velocity profile gradually.

5- Use appropriate control cards including control shell/solid/hourglass. You check the LS-DYNA user’s manual Vol.1 (LSDYNA Manuals) for more information. 

6- Use appropriate element formulations to better handle large deformations (Avoid fully integration elements, which is more vulnerable to negative volume element error). 

7- Reduce the mass or time scaling in the simulation.

8 - Ensure the units of the parameters input to your model are consistent (https://www.dynasupport.com/howtos/general/consistent-units).

I hope these tips are helpful.

Thanks,

Pedram

 

 

 

[panjc]

Hello

I use the different material model in simulation,turn the mat003 plastic kinematic to mat098 simplified johnson cook and increase the hardening value.the deformation decrease but it still unreasonable.its deformation like the  wave swing. Is this due to the inertia of rotation?or mass scaling?how can I fix it?

Thanks

[Pedram Samadian]

Hi,

It can have several reasons, including large time steps, inappropriate material model, contact issue, and so on. Please use the provided advice in the previous comments. For mass scaling, use the *CONTROL_TIMESTEP card in the LS-DYNA to ensure the time step adheres to the Courant’s stability criterion. Revisit the defined contact parameters. Use a proper value for the parameter “Soft” in the optional card A for the contact defintion. 

Details about the mentioned cards can be found in the LS-DYNA Keyword User’s Manual Vol. 1 (LSDYNA Manuals).

Thanks,

Pedram