HDPE Damage Criteria

[antchr]

Hello, I’m trying to simulate the cutting process of HDPE, and I’ve used ductile damage and shear damage initiation with values found in papers. The model works and the elements get deleted as the cutter progresses, however I am not noticing any chip formation with no chips flying off. There is noticeable plastic deformation however the elements just get deleted, could this be due to not enabling a specific parameter or having to use different criteria? I’m also using fracture energy as the damage evolution.

 

[FEA way]

I guess that you are using Abaqus. It's hard to say what's wrong without seeing the model. At least some screenshots would be necessary.

 

[antchr]

Hello yeah sorry I am using Abaqus. I didn't attach pictures because I was at work, I have attached some below. I am using Abaqus explicit,
I would ideally like to see chips forming, whether they are discontinuous or string like. Not sure if that's possible, or if I am using the wrong damage criteria. What other pictures would you like to see?

 

[FEA way]

Missing or physically incorrect chip formation in machining simulations is usually caused by wrong material parameters (especially plasticity and damage criteria), too coarse mesh, inaccurate representation of the geometry of the cutting tool (here you could try refining its mesh) or unrealistic process parameters (like cutting speed and feed rate).

 

[antchr]

Thanks for the detailed answer! I’ve used Johnson cook plasticity parameters, with a rate dependent hardening sub option. I could get actual plasticity data through tensile testing though(do you think that would be better?).

I have used ductile criteria with two rows for compressive and tensile values found online, with a fracture energy evolution law set to 0, as the curve in the paper I found just dropped to 0 on y and there was very small area under the curve when fracture occured. I’ve also used shear criterion, and enabled depvar (however I’m not 100% sure what this does).

I will try refining the tool mesh, does it need to be the same explicit element type as the pipe? It’s currently just standard element type. Also do you think there is a better damage criteria to use for polymers, as most tutorials I’ve seen online have been for metals and they’ve used JC damage parameters but I cannot find any values of these parameters online for polymers.

 

[FEA way]

The Standard/Explicit element library selection in Abaqus/CAE doesn't really matter, Abaqus will use proper elements automatically. Unfortunately, it can be hard to find reliable data for such specific material models for polymers. However, I would look for research papers, possibly involving Abaqus and similar topics because material model selection is also dependent on the simulated problem. The thing is also that JC model is meant for ductile materials like metals and polymers may need more advanced material models, often in the form of subroutines (like VUMAT).