Doubts regarding modelling of ceramics

[RAGHAV AGARWAL]

Hello Everyone,

I am modelling ceramics and have some doubts regarding that. I am using MAT_110 for Alumina (Al2O3). The model consists of 3D solid elements of ceramic and metal (Al) and a steel impactor. Both metals are modelled using the JC material model with linear EOS. I am using hourglass 5 (Qm=0.08) and TSSFAC = 0.9. I used the accuracy card and turned on hourglass energy in Control_energy. Eroding surface-to-surface card is used for interaction between impactor to ceramic and metal. Tiebreak contact (Automatic surface-to-surface tiebreak) was used to model the definition between the ceramic and metal plate. The simulation is been conducted on high velocities (300 - 800 m/s). Some doubts I have are:

1. D1 and D2 are damage parameters. If I don't enter the erosion criteria (FS or ADD_EROSION), the simulation doesn't work.  Why do we need damage parameters if materials is removed through erosion criteria? What's the difference between the both?

2. How to determine the erosion criteria and which parameter to be used for erosion (FS, MXEPS, EFEPS)? Most literature defines it as 0.06 for alumina. I am defining it for MXEPS but not getting good results. What is the best criterion that should be used for impacts on ceramics.

3. "https://www.dynalook.com/conferences/european-conf-2003/implementation-and-validation-of-the-johnson.pdf" defines erosion as total plastic strain (FS)  or if the negative value is entered, then it defines maximum tensile pressure at failure. What should be used and when?

Thankyou

[l...@schwer.net]

1\ MAT110 considers damage, i.e. weakening, of the material, As the material in an element looses strength, it can, and likely will, distort into configurations that will cause the time step to decrease or the simulation to halt. Such elements need to be removed from the simulation as they are both problematic and likely no longer will be contributing to the structural response.

 

2\ Erosion criteria, and their associated value, are nonunique and ad hoc. Considering that such criteria are dependent of mesh discretization, among other factors, perhaps you can see that three different meshes of the same simulation will require three different values of erosion criteria; to say nothing of erosion criteria themselves.

 

3\ See my response 1\ above.

 

                --len

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[lesz...@gmail.com]

Hi,

 

Can anyone else (apart from Len) confirm whether LS-PrePost > 4.12.0 works properly when using the mouse for rotating, zooming, panning, etc.?

 

There is no echo of actions in the Message window, although it was always present before. I have checked it on a few PC

 

 

Leszek

To view this discussion visit https://groups.google.com/d/msgid/ls-dyna2/000f01dc23fd%2467edd490%2437c97db0%24%40schwer.net.

[ziyande...@gmail.com]

How does ls-dyna handle contact after a pre-stress in a modal analysis (t=0, no contact, T=1 contact is closed and modes are extracted)?   Based on my simple model test, it doesn’t' seem to register the contact status at the start of an eigenvalue analysis.   I use control_implicit_eigenvalue with a negative load cuve ID to define when to extract the modes after an initial preload.      I am also looking into setting LCPACK = 3 in control_implicit_solver to see if that’s the root cause.

 

Overall, I am hoping to find some guidance documents on how contact works in a pre-stress modal analysis in LS-Dyna. 

 

Thanks 

 

 

From: ls-d...@googlegroups.com <ls-d...@googlegroups.com> On Behalf Of l...@schwer.net

Sent: Friday, September 12, 2025 10:54 AM
To: 'RAGHAV AGARWAL' <p202...@pilani.bits-pilani.ac.in>; 'LS-DYNA2' <ls-d...@googlegroups.com>

To view this discussion visit https://groups.google.com/d/msgid/ls-dyna2/000f01dc23fd%2467edd490%2437c97db0%24%40schwer.net.

[David Poulard]

Hi  Leszek, 

The option below was added. 

Users complained that the orientation messages were 'burying' the messages that they were actually interested in, like measure results.

Best

Dave

To view this discussion visit https://groups.google.com/d/msgid/ls-dyna2/006801dc2404%2498a74380%24c9f5ca80%24%40gmail.com.

[lesz...@gmail.com]

I am grateful for this suggestion – it really works.

Thank you very much.

Leszek