Hi Everyone,
I am working on 2D orthogonal machining with Johnson-Cook fracture model and using damage evolution in addition to this for accurate chip formation. There are 2 ways in which damage initiation can be implemented 1. by displacement 2. By Fracture energy. How can we choose the values for aforesaid ways. I asked some authors about this and they said we should select displacement in trail and error way so that chip, cutting forces match experimental values. Many of the reported literature discussed using fracture energy which can be calculated from fracture toughness. However, when tried as per Mabrouki et.al., (International Journal of Machine Tools & Manufacture 48 (2008) 1187– 1197), chips is discontinuous under same conditions. Can anyone help me out from this? Please look at the attached images of discontinuous chips in my simulation :-(
Abaqus/Explicit provides a dynamic failure model specifically for the Johnson-Cook plasticity model, which is suitable only for high-strain-rate deformation of metals. This model is referred to as the“Johnson-Cook dynamic failure model”.
The Johnson-Cook dynamic failure model is based on the value of the equivalent plastic strain at element integration points; failure is assumed to occur when the damage parameter exceeds true strain 1. The damage parameter is defined as "w".
Thus it is suggested to use damage initiation by displacement mode.
hello Prudvi Paresi , did you find the solution to your problem?
Currently i am going through the same problem can you please share how you solved this issue.
I think that Mabroukis parameters should in principle be fine. In comparing your results, make sure that your mesh is sufficiently fine (these simulations are very sensitive to mesh density); if your mesh density differs from that inj the literature, that alone may cause some deviation. BTW, the way you connect the chip and workpiece parts of the mesh looks weird to me.
If you want to form a continuous chip, you can also enforce this by only allowing elements at the separation line to fail.
Dear Martin baeker,
I am trying to get a continuous chip for similar machining condition and dealing with segmented chip problem. Can you kindly explain how to enforce element failure only on chip separation line. Should i need to define separate region at chip separation line of with single element thickness and give damage evaluation property to this region? what is the procedure?
Exactly, just define two materials, one that can fail, one that cannot, and assign the failure-material only to the layer in front of the tool.
Hi Martin,
You mean, we should not assign any failure/fracture criterion to chip layer? I think with out assigning failure criterion to chip layer, we don't end up with close results. Some times, simulation also aborts with high distortion due to severe plastic deformation in chip layer.
If you want a continuous chip, then failure in the chip region is not needed. The rest of your comment is too unspecific to say anything.
@prudvi paresi, define very small section on bottom of your chip and assign damage criteria and damage evaluation to only that region, thus you will get a continuous chip.
anyway how are you taking for damage evaluation, is there any method to find the fracture energy or displacement values
hello Prudvi Paresi ,
When we used the damage energy method as Mabrouki et.al., (International Journal of Machine Tools & Manufacture 48 (2008) 1187– 1197), a mesh dependence effect can be found. In addition, also their research (Zhang and Mabrouki et al. International Journal of Material Forming 2011, 4: 11–23) applied different mesh sizes to investigate the force sensitivity to mesh size, and it was found that simulation accuracy is affected by mesh size. Then our former work proposed an energy density based method to reduce the mesh dependence. Please find the contents in ( International Journal of Machine Tools and Manufacture. 2013, 75:16-26. ). I hope it can help.
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