Learning Forum

[Okkar Kyaw]

Hello every one! I am using effective plastic strain in tension region which is -1.32e-03. But if I want to use it in MAT add Erosion EFFEPS section. Should I put two negative to act as a failure criteria or just remove the + sign

[Armin]

 

 

Hi Okkar,

The effective plastic strain derived from the equation in your picture is always a positive value (check also this article: https://ftp.lstc.com/anonymous/outgoing/support/FAQ/effective_plastic_strain#:~:text=Characteristics%20of%20effective%20plastic%20strain,is%20on%20the%20yield%20surface.) 

However, to enable the failure criterion at particular effective plastic strain, you can input this value into the *MAT_ADD_EROSION card as a negative number for the EFFEPS variable and the model will consider it's magnitude or |EFFEPS| as the effective plastic strain at failure.

 

 

[Okkar Kyaw]

Hello, Amer, Thanks for the quick response. What I mean here is as shown on the photo. The effective plastic strain that I want to use is in tension region, and it shows the negative value. please check the photo. Shoul I use as it is. Thank you.

[Okkar Kyaw]

Please check the blue zone

[Armin]

Thanks Okkar for sharing this. That's interesting because to my understanding, the effective plastic strain is always non-negative which may indicate numerical problems here.

Could you mention what this material is? As a general observation, plastic strain in the range of 1e-3 displayed in your picture is pretty small and might be close to the onset of yielding of the material. As a reference, fracture strain of ductile materials is at least two order of magnitude larger than this value. 

[Okkar Kyaw]

Hello the material is ceramics and i am trying to simulate with a very small fracture strain here. It is not a ductile material. 

[Armin]

I see... I don't have much experience with fracture of brittle materials, but I think you can consider a stress-based approach for fracture (instead of strain-based) by setting the SIGP1 or SIGVM in the MAD_ADD_EROSION card to the desired fracture stress.