ABAQUS Ductile Damage Initiation Criterion

[hwa0725]

Hi all,

Not sure if it was just me who found the description for ductile damage in the ABAQUS manual a little confusing (perhaps misleading). From the example plot taken from ABAQUS manual, clearly, the damage is initiated at epsilon(0,p) and completely fractured at epsilon(f,pl). However, when it comes to filling the table in CAE, it asks for 'fracture' strain instead of strain at damage initiation... It was very confusing until reading this post here Link (thanks OP and gents answered to this)

Now let's dive into my question after all the complaints.. Suppose I have conducted the uniaxial tensile test and plotted the engineering and true stress-strain curves as below. Is the true strain corresponding to engineering strain where the necking occurs (i.e. peak engineering stress) my strain at damage initiation (A.K.A. Fracture strain by ABAQUS)?

Also, since the formulas to convert stress & strain from engineering to true value only hold up to necking, how am I supposed to find out epsilon(f,pl)? Note, from the plot I have below, I continue using the formulas beyond necking even though they are no longer valid. I suppose what I am trying to ask is how to find out the actual true stress-strain profile after necking to calculate the fracture energy required for damage evolution in ABAQUS?

Thanks a mil,

Heng

 

[FEA way]

There's a good YouTube video covering those concepts with an example - "The ultimate quick guide to damage for ductile metals - ductile damage for ABAQUS CAE" by R. Wagner. Check it out.

 

[hwa0725]

Hi FEA way,

Yes, I did watch the video. What I don't understand is how he got the true stress-strain profile after the necking. Surely those formulas to calculate true stress & strain from engineering values don't work beyond the necking.

Thanks,

Heng

 

[FEA way]

Determining this accurately would require proper additional measurements during a real-life test. If they weren't done then you can either look for some research papers describing the approximation of true stress-strain after necking (there are a few articles about this) or rely on those simple formulas (like the YouTube guy probably did but maybe ask him to be sure).

 

[hwa0725]

Thank you FEA way, I will have a look at the journal again and see if I can find anything useful.