Beam Element

I want to do a finite element analysis of the braid vessel stent model with the B31 beam element and the explicit solver, and I find that the wires in the analysis are discontinuous. Should I add some constraints or cross-sectional connections?

I set the radial displacement of all the nodes, as usual the stent should be extended, but the result was not, and the lines became independent segments.

What's the best open source FE code for nonlinear transient analysis of truss structures (preferably with Python interface)?

Are there analytical expressions for computing von Mises or equivalent stress at any point for Beam elements similar to the ones in continuum elements? I would like to design a structure with beam elements and ensure that the equivalent stress is within bounds (yield stress etc) for the structure to be safe.

I am interested in using beam element to do a nonlinear static analysis (may need to a dynamic analysis in the future), but have trouble to understand some of the key features of beam element in abaqus or ansys. My goal is to find a beam element (preferably general beam section) with a defined stress resultant yield surface (e.g., P-M-M yield surface). If possible, could also account warping degree of freedom.

ABAQUS