Stable increment time too low

[FEMbiaatch]

Hello,

I am running a quasi-static analysis of medical needle penetration into a thermoplastic polyurethane material (0.4mm thick) using cohesive zone modeling in Abaqus Explicit solver.

The whole analysis will last for 3 seconds. The problem is that my stable time increment is very small. It is 8.14e-9 seconds. I'm using a visco-hyperelastic material model for the polyurethane calibrated using experimental measurements, and my needle is modeled to be rigid. I know that the smallest element length affects Abaqus's stable time increment algorithm, but I'm using a reasonably coarse mesh. From the preliminary examinations using verify mesh, it seems that I can't increase the stable time increment beyond 1e-9 seconds for my chosen material properties. Mass scaling does improve the time increment but not that substantial. Is there any other way to increase stable time increment?

Thank you.

 

[FEA way]

I would say that the mesh is quite dense for an explicit dynamics analysis. Maybe you could coarsen it a bit (especially in farther parts of the needle that likely aren't of such interest as the tip) or make use of some simplifying assumptions like symmetry or shell modeling. Also, localize the element/elements with the lowest stable time increment. You can apply larger mass scaling just to those elements. You could also try speeding up the process artificially. Just make sure that kinetic energy is low enough so that the analysis is still quasi-static.