The top edge of a 1 by 1 plate is sheared over 0.01 to the right, and the bottom edge of the plate is sheared over a distance 0.01 to the left. The material cannot sustain positive principal stress exceeding 0.002 -- it cracks. This cracking is modeled with a plasticity model which does not allow for principal stresses exceeding 0.002; the group_materi_plasti_tension model is used for this. The plate is modeled with linear triangles (-tria3). The first plot below shows the (deformed) mesh.
The second plot below shows the largest positive principal stress; notice that this principal stress did become equal to 0.002 over the entire tension diagonal.
The third plot below shows the plastic strain; plastic strain does show up especially in the corners of the tension diagonal.