Hello,

I am trying to model a Representative Volume element (RVE) of a composite with polyamide 6 and Continuous fibres. While I initially had the GTN model in mind, it was suggested to use the Abaqus Ductile Metal damage model (what I like about it is the possibility to delete elements even in implicit).

From a tensile test I got the  curve shown in the first picture[Grubenmann 2018], the orange curve shows true stress-strain but is only valid up to 0.3 (at which necking is assumed to start). The plasticity data I took from that graph is shown in the second picture with a damage onset at a strain of 0.27

Since ultimately I want to model on the micrometer scale I set up the test model (to verify if the Ductile Damage model works by itself) on the µm scale as well. The dogbone has a length of 20µm and a thickness of 0.2µm (one element in thickness direction). I am using Wedge elements as I have to use them later on as well with a side length of 0.2µm.

I calculate the characteristic length by dividing the elements volume by the largest surface, which results in Lc = 0.0866 µm. 

The area under the graph marked by the green box is roughly 11.3 MPa. The Fracture Energy is calculated as the area*characteristic length = 0.979 N/m

With this I can calculate the displacement of failure as uf = 2*FractureEnergy/SigmaYield=32.7µm

The shown bar is 20µm long. With a displacement of 20µm the calculation works without errors but the result looks pretty strange. Since I activated element deletion I suspected the elements to fail and the two parts to separate, but they don't.

E:  m to µm is 10^-6 and not 10^-9...

Before I made this post I read the manual, watched several tutorials but can't find where I am wrong. The same behavior occurs with HEX elements.

E: I added an SDEG plot. Since the value isn't close to 1 I most likely made a mistake calculating my displacement of failure length.