Hello,

I am simulating a perforated structural tube (image attached; composite in red) subjected to pure bending (I am rotating both ends by 2°). The perforation is repaired with bidirectional fiber-reinforced composite (Hashin: XT=256MPa, XC=153, YT=132, YC=161, SL=67, ST=48) so as to try and recover the tube's intact resistance to bending.

The simulation converges when damage evolution is not used, but it aborts when I set the damage evolution (fracture energies: Gft=10.937, Gfc=7.02, Gmt=17.649, Gmc=11.44, viscosity parameter 1e-4). I am using a 4mm mesh on the composite.

Some additional info:

>I'm using Abaqus Standard, static general, mintstep 1e-30, maxtstep=0.02, stepini=0.0001, time period=1 (have also tried Riks, similar step parameters, got similar results);

>NLGEOM is on;

>In the General Solution Controls Editor, discontinuous analysis is toggled on and the number of attempts before cutback is increased from 5 to 30;

About some of my results:

>It converges for:

-->>Coarse mesh (composite 50mm);

-->>Fine mesh (composite 4mm) with high viscosity parameter (1e-1);

-->>Simulations without damage evolution (Hashin criteria only);

-->>Thicker laminates (damage doesn't start)

>It doesn't converge for:

-->>Fine mesh with small viscosity parameter (1e-4)

-->>Thin laminates (as I see, damage escalates quicker with thin laminates)

>The error that shows for non-convergence:

-->>Too many attempts made for this increment (eventhough I increased the number of increments before cutback and the time step goes as small as 1e-25, it still doesn't converge).

Some warnings shown (for converged and non-converged simulations):

-->>Output request damagec is not available for the material for element type s4r

-->>Element type s4r has no output at section point 7. Section point removed

-->>The strain increment has exceeded fifty times the strain to cause first yield at 1688 points

I understand Abaqus manual ( https://abaqus-docs.mit.edu/2017/English/SIMACAEMATRefMap/simamat-c-damageevolfibercomposite.htm ) describes a correction for the fracture energy with respect to element characteristic length. I have also read the Lapczyk article about it. What I don't get is if Abaqus does this correction automatically and I must only input the fracture energy as it is OR if I should correct the fracture energy input every time I change the mesh size for the composite.

Would anyone know it doesn't converge?

Thanks in advance. Please, feel free to ask any info about the problem.