Hi all

I am using a B31 circular beam element to model a steel dowel in timber embedment.
As I am trying to model large deformations, the behavior of the beam after yielding is especially interesting to me.

Do beam elements consider the reduction of cross-section, the necking, or is it a fixed dimension?
Without in-plane deformations, true stress-strain relation shouldnt be used for the material definition i suppose.

I found the following section in the manual but am not sure if this "constant change" applies here. 
"The fundamental assumption used is that the beam section (the intersection of the beam with a plane that is perpendicular to the beam axis; see the discussion in Choosing a beam cross-section) cannot deform in its own plane (except for a constant change in cross-sectional area, which may be introduced in geometrically nonlinear analysis and causes a strain that is the same in all directions in the plane of the section). " 

Thanks in advance for any help on this!
- Alex

Abaqus ​​​​​​​