Output coordinate system

You can easily check it by enabling Common Plot Options —> Normals —> Show normals in Viewer. You can also create a symbol plot of section force results.

"post-deformation beam local coordinate system" ... sounds like large displacements.

I'd've thought the default axes system was the element axes (not global, though I suspect you can get global output).

I'd've thought that the element axes doesn't change if displacements are small.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

in ABAQUS help document, it is "Element-based results for beam and truss elements cannot be transformed; they are always displayed in the local

element orientation system. ".

In the figure below, when the beam element has a large displacement, the local coordinate is which of the coordinates a or b in the figure?

Depends on the specific output variable.
Element results like forces and stresses are output in the element coordinate system.
Nodal results such as displacements are output in the nodal coordinate system, which can be either the global coord system or a local coord system. For large displacement analyses, I think there is an option to output nodal results in the displaced coordinate orientations.

I think b) only if large displacements is turned on. Normal (small displacements) is a) ... the elements don't displace (in a global sense).

But in any case the internal loads are still applied in the element local axes ... the local axes deflect with the element ... "t" is tension in both cases.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.