Learning Forum

[Raghav]

Hello everyone,

I am modelling impacts on ceramics and have some doubts regarding that. I am using MAT_110 for Alumina (Al2O3). The model consist of cermic and metal (Al) and steel impactor. Both the metals are using JC material model with linear EOS. I am using hourglass 5 (Qm=0.08) and TSSFAC =0.9. I used accuracy card and turned on the hourglass energy in control_energy. I am using Eroding contacts for ceramic and metal against the impactor and Automatic surface to surface between ceramic and metal plate. Some doubts I have are:-

1. Is MAT_ADD_EROSION necessary for ceramic modelling? When i didnt used the erosion card, the penetration is not happening and my projectile is simply passing through the ceramic plate. Or do I have to improvise my contact definations.
2. How to determine the erosion criteria and which parameter to use for the erosion (MXEPS, EFEPS etc.)? Most literature defines it as 0.06 for Alumina. I am defing it for MXEPS but not getting good results. What is the best erosion criteria that should be used for for simulating ceramic impacts?
3. https://www.dynalook.com/conferences/european-conf-2003/implementation-and-validation-of-the-johnson.pdf defines erosion for ceramics as total plastic strain (FS) or if the value is enetered as negative then it represents maximum tensile pressure. Which criteria should be used and when?
4. Is there any standard ceramic-metal armor paper for impact analysis as there may be a chance I am modelling metal incorrectly.

Thankyou

[Ram Gopisetti]

Hi

MAT_110 includes inbuilt support for D1, D2, and FS to account for damage and erosion. Therefore, unless you have specific parameters provided by MAT_ADD_EROSION, its definition can be omitted. However, please verify this with your reference documentation and apply sound engineering judgment.

The projectile speed is not specified, but if it is relatively high, I recommend reducing the tssfac to 0.7 or lower. Additionally, consider increasing the stiffness parameters within the contact definitions. Use AUTOMATIC_SURFACE_TO_SURFACE contact and include *CONTACT_INTERIOR for improved simulation accuracy.

Given that ceramics are brittle materials and perform better under compression than tension, strain-based failure criteria are more appropriate than stress-based ones. You should adjust these criteria to align with the values reported in the reference.

As stated clearly in the MANUAL VOL2, if FS < 0, failure occurs in tension, while FS > 0 indicates failure by effective plastic strain.

Please check this paper https://lsdyna.ansys.com/wp-content/uploads/attachments/14-5.pdf

Cheers, Ram